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The reproductive behavior and ecology of the white ibis (Eudocimus albus)

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Title:
The reproductive behavior and ecology of the white ibis (Eudocimus albus)
Creator:
Rudegeair, Thomas James, 1948-
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Language:
English
Physical Description:
x, 147 leaves. : illus. ; 28 cm.

Subjects

Subjects / Keywords:
Bird nesting ( jstor )
Birds ( jstor )
Eggs ( jstor )
Female animals ( jstor )
Head ( jstor )
Mating behavior ( jstor )
Neck ( jstor )
Nesting sites ( jstor )
Seas ( jstor )
Storks ( jstor )
Dissertations, Academic -- Zoology -- UF
Ibises ( lcsh )
Zoology thesis Ph. D
Gulf of Mexico ( local )
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bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis -- University of Florida.
Bibliography:
Bibliography: leaves 144-146.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Thomas J. Rudegeair.

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THE REPRODUCTIVE BEHAVIOR AND ECOLOGY OF THE
WHITE IBIS (EUDOCIMUS ALBUS)
















By

THOMAS J. RUDEGEAIR, JR.












A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY




UNIVERSITY OF FLORIDA 1975












ACKNOWLEDGMENTS

I would like to express my gratitude to my advisory committee, Jack Kaufmann, Jim Lloyd and David Johnston, who guided me during the collection of data and the writing of this dissertation. Thomas Emmel and Thomas Patton, who reviewed my work have also been of particular assistance.

My work on Sea Horse Key was greatly aided by Edward Collingsworth, who granted me permission to work there, and Frank Maturo, Lee Belcher, and A. D. Folks who provided transportation and made living on the island comfortable.

Study of the Biven's Arm rookery was made possible through the kindness of Jim Wing, who donated the use of his boats.

I must also include thanks to my friends for their moral support, especially Donna Gillis and all who assisted me with data collecting. My wife, Frannie, deserves special mention. She helped me in the field, in the preparation of rough drafts, and in solving all resultant problems. She was my inspiration.

Support for my research was provided by the Department of Zoology of the University of Florida, an estuarine studies grant from the Division of Biological Sciences and a grant from the Frank M. Chapman Memorial Fund of the American Museum of Natural History.













TABLE OF CONTENTS

Page

Acknowledgments . . . . . . . . . . . . ii

List of Tables ................... . . . .. v

List of Figures. ................... . . . vii

Abstract . . . . . . . . . . . . . . viii

Introduction . . . . . . . . . . . . . 1

The Study Areas. . . . . . ... ... . . . . . . 3

Sea Horse Key. . . . . . . . . . . . 3
Biven's Arm . . . . . . . . . . . ... 8

Methods . . . . . . . . . . . . . . 11

Morphological Description and Major Preening Movements .... . 14

Results. . . . . . . . . . . . . . . . . 16

The Season . . . . . . .. . . . . . 16
Numerical Increase on Sea Horse Key . . . . ...... 16
Aggression . . . . . . . . . . . . 21
Pair Formation . . . . . . . . . . . 26
Copulation . . . . . . . . . . . . .. 38
Nest Building . . . . . . . . . . . . 46
Egg Laying . . . . . . . . . . . . 58
Incubation . . . . . . . . . . . . . 60
Behavior of Young .. . . . . . . . . . . . 67
Comparisons Within the Order . . . . . . . . 82

Discussion . . . . . . ... . .. .. . ... 92

Comparison of the Study Areas... . . . . . . . 92
Habitat Comparison . . . . .. . .. . . .. . 93
Pre-Pair Formation Behavior. . . . . . . . . 96
Pair Formation-Aggression . . . . . . .. .... 96
Analysis of Pair Formation Displays . . . . . . 97
Copulation . . . . . . . .. .. .. . 105
Mating System . . . . . . . . . .. . . . 107










Nest Building. . . . . . . . . . . .
Incubation ................ ... .... . . 114
Hatching and Early Life. ................. 115
Comparisons Within the Order ................ 119

Summary . . . . . . . . . . . . . . 121

Plates . . . . . . . . . . . . .... 124

Literature Cited . . . . . . . . . . . . 144

Biographical Sketch. .................. ..... 147










































iv













LIST OF TABLES

Tables Page

1 Dates of first occurrences of nesting events
for both localities. . . . . . . . . . . 17

2 Dates of key nesting events for 12 specific
nests on Biven's Arm (1973) ... .. ......... . 18

3 Mean ambient temperatures for the months
preceeding breeding. ................... 19

4 Pair formation activities of 15 males and 25 females .... 28

5 Rates of performance of male pair formation
activities (15 males total); comparison of
each year and both sites . . . . . . .. .. 31

6 Temporal relationships of main pair formation
activities between male and female ............ 33

7 Initial behavior of displaying male when female
approaches and immediately prior to her departure. ... 36

8 Pre-copulatory activities, both sexes. ..... . . 39

9 Post-copulatory activities male and female ....... 41 10 Intercopulatory intervals. ................. 44

11 Division of labor for twig placement following
male return with nest material ........... ... 52

12 Nest site data . . . . . . . . . . . .

13 Data on nesting trees. . .. . . . . . . . 55

14 Mean and standard deviation (s) of nest heights
for cluster of synchronized nest and overall
values ................. . . . . . ...... . 56

15 Mean and standard deviation (s) of nest diameters
for clusters of synchronized nests and overall
values .. .. . . . . . . .. . . . . 57

16 Clutch size data for Sea Horse and Biven's Arm, and from
inland Florida sites (from the Florida State Museum egg
collection) . . . . . . . . . . . 59









17 Minutes off the eggs (inattentiveness) for the
block of time 1200-1500 hrs . . . . . . . . 63

18 Rate of performance of activities during incubation
period . . . . . . . . . . . .65

19 Feeding rates of young for Sea Horse and Biven's Arm .... 71 20 Feeding intervals Sea Horse vs. Biven's Arm and
Biven's Arm early vs. late in season for young of
two age groups . . . . . . . . . . . 73

21 Composite calculation of seconds of feeding/day at
Sea Horse and Biven's Arm, based on data from
Tables 18 and 19 . . . . . . . . . . 74

22 Growth rates to 5 days for young from 6 nests on
Biven's Arm late in the 1973 season . . . . . . 76

23 Survival rates of young to 10 days ............ 83

24 Comparison of the displays of the White Ibis and
four groups of storks (Ciconiidae) . . . . . . 85

25 Comparison of the displays of the White Ibis and
four heron species (Ardeidae) . . . . . . . 86


























vi













LIST OF FIGURES

Figure Page

1 Sea Horse Key and surrounding area ........... 4

2 Sea Horse Key (vegetation) ............... 6

3 Number of ibises arriving through the day at
Sea Horse: 14 March 1974 (pre-pair formation). ....... 20

4 Profile of a White Ibis flock in flight. . ........ 22

5 Sea Horse Key approach routes and favored roosts .... 23 6 Copulations per hour ................ . 42

7 Sea Horse Key map of nesting areas and the order
of settlement of island areas. ............... 48

8 Minutes off the eggs (inattentiveness) during
incubation vs. time of day; temperature vs. time
of day . . . . . . . . . . . . . 61

9 Minutes off the eggs during incubation vs. day
of incubation. . . . . . . . . . . . 62

10 Young in the basin at Sea Horse vs. time
of day ............ ............... 81






















vii











Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy


THE REPRODUCTIVE BEHAVIOR AND ECOLOGY OF THE WHITE IBIS (EUDOCIMUS ALBUS)

By

Thomas J. Rudegeair, Jr.

March, 1975

Chairman: John H. Kaufmann
Major Department: Zoology

The behavior and ecology of the White Ibis, Eudocimus albus, was studied during the breeding seasons of 1971 through 1974 at two locations in central Florida, an island in the Gulf of Mexico (Sea Horse Key) and an inland lake (Biven's Arm). Quantitative data were collected on many phases of the ibises' reproductive behavior, including; arrival at the breeding grounds, aggression, pair formation, copulation, nest building, incubation and care of the young.

The breeding season extends from early March until August, beginning earlier at the Sea Horse rookery. Following initial numerical increases at the rookeries, males select display sites and defend them aggressively. They then advertise with the Snap Display, Head Rolling and Display Preening. The females land nearby, face the male, and perform Head Rolling and Display Preening, exposing the swollen gular pouch to the male. Mate selection is mutual, as the females approach the stationary males. Partners greet at the nest with the Up-Down display.




viii










The displays of the pair-forming White Ibis are quite similar to those of the Storks, but quite different from those of the herons.

The first copulation marks the formation of the White Ibis pair. Copulation occurs for five days and terminates with the laying of the first egg. Both paired males and females copulate promiscuously with birds from neighboring nests. Only the males gather nest material and their collection strategy appears designed to permit observation of their own females. Males violently oppose promiscuous mating attempts directed toward their mates.

The ibises nest in hardwood trees on both study sites. The

Sea Horse population nested in distinct clusters of pairs and settled different areas of the island in a consistent pattern each year.

Clutch sizes averaged 2.1 at Sea Horse, 2.9 at Biven's Arm early in the breeding season, and 2.2 at Biven's Arm late in the season.

The incubation period is 21 days with parents alternating at the nest site. The extent of inattentiveness to the eggs is strongly correlated with temperature.

The young are fed by direct regurgitation and one parent remains with them at all times until day 10. Individual recognition develops simultaneously with the mobility of the young. Rates of feeding on Sea Horse are lower than Biven's Arm, reflecting the longer distance the Sea Horse adults must travel to obtain food. At five weeks of age the young are fed in the tree tops by the returning parent and are forced to pursue the adult over increasingly longer distances.

Between feedings on Sea Horse, flocks of six and seven week-old young birds feed on the mud flats around the island. They are capable



ix









of establishing a linear dominance hierarchy that apparently determines access to limited food sources. Their feeding activities through the day are correlated with tidal and temperature fluctuations.














































x













INTRODUCTION


The behavior of the members of the avian order Ciconiiformes has been extensively studied in recent years. Andrew Meyerriecks (1960), for example, has closely examined the breeding behavior of four species of herons (Ardeidae) and M. P. Kahl (1966, 1972a, 1972b, 1972c, 1972d, 1973) has studied the reproductive displays of the storks (Ciconiidae). A third family in the order has been largely ignored, however. The behavior of the ibises (Threskiornithidae; subfamily, Threskiornithinae), represented worldwide by some 26 species, has been studied by only a few workers. The published reports contain only brief qualitative descriptions of breeding activities; e.g., ffrench and Haverschmidt (1970) on the Scarlet Ibis (Edcdoimus ruber), Skead (1951) on the Hadedah Ibis (Hagedashia hagedash), Beebe (1914) on the White Ibis (Eudocimus albus) in captivity, and Meyerriecks (in Palmer, 1962) on the White Ibis.

This study reveals the reproductive behavior of the White Ibis

in quantitative detail including arrival at the breeding area, aggression and pair formation, details of the mating system, copulation, nesting strategies, incubation, and raising of the young. Also examined are the effects of such ecological parameters as varying predation pressure, food availability, and nest site availability.

Two sites close to the University of Florida campus, an isolated island in the Gulf of Mexico (Sea Horse Key) and an inland lake (Biven's



1









Arm) provide contrasting habitats for nesting White Ibises. Consequently, they provide an opportunity to learn of the behavior of a common but little-studied species and to simultaneously compare that behavior in two distinct ecological settings.

The discussion emphasizes the adaptive significance of the basic reproductive strategies employed and the environmental causes for the differences observed in the two populations. The mating system of the ibis (monogamy with subsequent mutual promiscuity) is discussed at length and its possible merits reviewed. Also presented is a brief summary of the ethological theory of the origin and evolution of displays, and a consideration of the ibises' pair formation displays in that context.













THE STUDY AREAS


Sea Horse Key


Sea Horse Key is a 154-acre island 2.5 miles southwest of

Cedar Key on Florida's Gulf Coast, and approximately 5.5 miles from the Florida mainland. Figure 1 shows the position of Sea Horse and the three other islands that collectively comprise the Cedar Keys National Wildlife Refuge: Snake Key, North Key, and Deadman's Key. Sea Horse Key is a remnant of a Pleistocene sand dune formed at a time when the water level was greatly reduced (Wharton, 1958). The waters around the island are diluted due to the fresh water influx from the Suwanee River and the Wacassassa River, and support a typical estuarine fauna and flora.

Sea Horse is surrounded by extensive tidal flats upon which turtle grass (Tha assia testudinum) and manatee grass (Syringodium filiforme) grow in abundance. In the winter and early spring these grass flats are covered by only very sparse vegetation, and the associated epifauna is reduced. By late May the grasses are extensive, and crustaceans and polychaetes abound on and under the surface. Along the northern shore where a channel has been dredged, the mud banks and oyster beds exposed at low tide provide potential feeding areas for the White Ibis.

These sites in the intertidal zone around the island provide

a limited amount of food for the ibises, especially late in the breed3























NORTH
KEY ATSENA OTIE N KEY


DEADMAN's KEY



SSca SNAKE KEY
0 1/2 1
miles SEA HORSE KEY :
miles


Figure 1. Sea Horse Key and surrounding area. Snake, North and Sea Horse Keys comprise
the Cedar Keys wilderness study area (from Wharton, 1958).




5




ing season, but the bulk of the food for the young must be obtained from the brackish marshes along the mainland coast. The round trip is a minimum of eight miles and feeding flocks have been observed as far inland as Otter Creek, 20 miles east of Cedar Key.

Nesbitt et al. (1974) report stomach contents of 46 White Ibises nesting near salt water in Florida (30 from Sea Horse). Crayfish (Procambarus sp.) were found in 44.1% (by volume) of the stomachs, crabs (primarily Uca spp.) in 23.4%, and insects (eight orders) in 24.3%. Vertebrates were less prevalent; fish were found in 1.0%, reptiles (primarily snakes) in 3.0%, and no amphibians.

Sea Horse Key slopes upward from the north and south shores to a central ridge running in an east-west direction. Wharton (1958) describes the flora of the island and the micro-habitat differences of the northern and southern slopes. His work is the source for the scientific names of the trees mentioned in this study. The ibises nest on the slopes in the trees of the oak and bay-dominated hardwood hammock that thrives there (Figure 2). These 60 acres of potential nest sites have supported as many as 200,000 White Ibises (in 1972, according to the staff of the Chassahowitzka Wildlife Refuge) since the island was first used for nesting in 1960. Nests are constructed in six species of trees at heights ranging from 2.5 to 40 feet. The forest floor is open in most areas and its wealth of fallen twigs readily accessible to nest-building birds.

There was virtually no interspecific competition for nest sites

or materials observed on Sea Horse. The ibises nest only on the central ridge whereas the herons and egrets, including the Great Egrets











M Scale
0 feet 446 HER
M
NORTH WEST COVER'
GARDNER'S ARM



HER M ) M


SMangroves E M HER M.

Study Area

HER Heronry C Cormorant-Pelican Nesting

Ibis nesting area (hardwood community)


Figure 2. Sea Horse Key, showing vegetation and sites of rookeries (modified from
Wharton, 1958).




7



(Casmerodius albus), Black-crowned Night Herons (Nycticorax nycticorax), Yellow-crowned Night Herons (Nyetanassa violacea), Little Blue Herons (Florida caerulea), Louisiana Herons (Hydranassa tricolor ruficollis), and Snowy Egrets (Egretta thuZa) nest exclusively on the peninsula of land extending north from the western end of the ridge (Gardner's Arm) and in the black mangroves (Avicennia nitidia) along the island's north shore.

There is little danger to nesting ibises on the island. The only mammals present are the black rat (Rattus rattus) and the gray squirrel (Scuirus carolinensis). Among the reptiles, only the locally abundant cottonmouth moccasin (Agkistrodon piscivorus) is potentially dangerous, and only to individuals on the ground. Of the avifauna, the Osprey (Pandion haliaetus) and the Bald Eagle (Haliaeetus leucocephalus) are large enough to potentially be of harm to the adults, but the eagle is only a rare visitor and the Osprey, while locally abundant, interacts very little with the ibises.

The eggs and young of the ibises are in greater danger. Several hundred Fish Crows (Corvus ossifragus) on the island are constantly present in the rookery and are frequently seen flying with eggs in their bills. At hatching, the threat from the crows declines but predation by the Black-crowned Night Heron begins. This species has been observed challenging adult White Ibises at their nest sites for access to the young, rather than merely waiting for an exposed nest as the Fish Crows do. The effects of the rats on eggs and small young are unknown. If a nestling should fall to the ground it is subject to predation by the cottonmouth.




8




Biven's Arm


Biven's Arm is a 200-acre lake in Gainesville with drainage

onto Paynes Prairie to the southeast. Surrounding the lake is a zone of small red maples (Acer rubrum) and elders (Sambucus canadensis) approximately 30 feet in width. On the southwest side of the lake, this zone takes the form of a series of small floating islands, most of which are separated from the shore by a narrow water or mud barrier (depending upon rainfall). Numerous fallen trees, however, usually render these islands accessible to mammalian predators. Immediately behind this zone of small trees, on the shore itself, are towering oak trees (Quercus sp.). While often roosting in these trees, the ibises nest exclusively in the small maples and elders near the water (Plate 2b).

Paynes Prairie is an extensive 9,000-acre fresh water marsh

.that lies approximately 1.5 miles south of Biven's Arm. It provides feeding grounds for the ibises near the nesting area. Nesbitt et al. (1974) also report stomach contents for 125 White Ibises nesting near fresh water (21 from Biven's Arm). Crayfish were found in 45.3% of the stomachs, insects (six orders) in 36.7%, and no crabs at all were found. Fish constituted 0.7%, reptiles, 3.3%, and amphibians 1.2%.

Unlike the segregation observed on Sea Horse Key, the herons and egrets nest in the same areas as the ibises on Biven's Arm. The entire nesting area for all Ciconiiform birds is less than 10 acres. The red maples reach a height of about 15 feet and the elders are less than 10 feet. This initial limitation on the number of potential nest sites is accentuated by the presence of the competing herons, all of which




9




select sites and have similar nesting requirements. An estimated maximum of nesting White Ibis pairs on Biven's Arm was 200 in 1972.

Nearby Lake Alice on the University of Florida campus provided nesting sites for the ibises until the degredation of the area in the early 1960s, at which time the birds discontinued nesting. Simultaneously, the previously unused Biven's Arm area became the site of an active rookery. In recent years, however, the lake has attracted land developers. As a result, the buffer zone between the birds and the human population has decreased and human use of the lake has increased. In 1974 an estimated 30 pairs of ibises fledged young from the Biven's Arm rookery.

Whereas the number of ibises in the area is low, the pairs nest in close proximity (nearest neighbor 1.8 feet) and, with the addition of nesting Little Blue Herons, Louisiana Herons, Snowy Egrets, and Cattle Egrets (ArdeoZa ibis), there is considerable competition for space and materials. Despite this density of nesting birds, Biven's Arm has at least one advantage. The vast feeding grounds on Paynes Prairie reduce the time and energy that must be spent flying to gather food for the young.

The only predators observed on the nesting grounds were two

mammalian species. Raccoons (Procyon lotor) and domestic cats (Felis domestica) were both observed near the rookery and are presumably responsible for the large scale nest abandonments and destruction that occur periodically. The stunted nature of the vegetation prevents escape from such predation. There is apparently very little avian predation of the ibises' eggs or young on Biven's Arm. Although Fish Crows are




10




plentiful in Gainesville, they were never observed at the rookery. The predacious Night Heron that is so damaging to the young ibises on Sea Horse was not observed during this study on Biven's Arm. Other potential avian predators, such as owls and hawks, are also apparently absent from the area of the rookery. Alligators and snakes may constitute a threat to birds on the ground.













METHODS


Because Sea Horse Key is a National Wildlife Refuge, working within the hammock is discouraged. Throughout the breeding season the adult ibises are extremely wary. During pair formation nest sites are readily abandoned, and later in the season eggs and young are left exposed to Fish Crows and Night Herons for at least several minutes, if the adults are disturbed. As a result, all of my observations were taken from at least 50 feet with the aid of 7 X 50 and 7-15 X 50 zoom binoculars. I observed from the edge of the trees and from the catwalk around the lighthouse tower situated in the center of the clearing on the crest of the main ridge. The tower is built into a large house that has windows which afforded closer observations of many activities, although their low position made observation of the nest contents impossible. Tripods were employed on the tower and from the windows, and various behaviors were recorded with a Bolex 250 Macrozoom (8:1) super-8 mm movie camera and a Mamiya/Sekor 1000 DTL 35 mm single lens reflex camera, with either a 400 mm or 900 mm telephoto lens attached. Notes were taken on both a Norelco Cassette Recorder and by hand, often with the aid of assistants. Stop watches were used to determine the duration of behaviors, and a wrist watch to record the time of day. During incubation, thermometers and a three-lead theromgraph were used to determine ambient temperatures in the study area.

Clutch sizes were obtained by single trips through the rookery each year. I moved as quickly as possible to minimize the length of


11




12




time each adult was off the nest. All nest site data were collected in the winter months.

On Biven's Arm, observations were made from a rowboat anchored

50 feet from the nest sites. The same recording and optical equipment was employed here. With the absence of avian predators, disturbance of the nest site was less destructive here than on Sea Horse since the nestlings were not subject to attack. This permitted daily visits and determination of intervals between eggs, both at laying and hatching, and growth rates of the young. Nest site parameters were measured at the same time.

Durations of rapidly occurring behaviors were determined by photographing activities at 18 frames per second and subsequently counting the number of frames spanned by each. Data throughout are presented as mean values (designated as x) with the sample size (designated as "n") from which the mean was calculated. Ranges or standard deviations (designated as "s") are included for most activities.

During pair formation, I selected individual males for observation based on accessibility. These males were watched intensely through formation of the pair or abandonment. Simultaneous data were collected on associated females, including all motor patterns and the timing and description of approaches to the male.

Attention was directed toward the details of copulatory behavior and related activities during the four-year study. In addition to spot observations on most of the pairs on Biven's Arm and the clearing on Sea Horse, several were observed continuously over three or more days




13




of the five-day copulatory period. For each copulation the time, duration, pre- and post-copulatory events, and associated behaviors were recorded. From these data a detailed description of the White Ibises' behavior during the copulation period was possible, including copulation rates, intercopulatory intervals, and the extent of promiscuity.

During the 1971 season six nests on Sea Horse were observed on 10 of the 21 days of the incubation period, and all activities of the adults were recorded. From this record, taken as early as 1/2 hour before dawn until darkness, a complete description of incubation behavior could be generated. The data reveal when each bird stood over the eggs, what he or she did while up, and when each one resumed incubation. The rate and dynamics of the exchanges of the adults at the nest site were also recorded.

Unless otherwise stated, the descriptions of the behavior of

the White Ibis are a result of data from both study areas, and generalizations apply to both. Details are presented for behaviors that differ between the populations.













MORPHOLOGICAL DESCRIPTION AND MAJOR PREENING MOVEMENTS

The adult is white, with black tips on four outer primaries. Some of the breeding ibises show a slight buffy wash on the crown. Outside the breeding season the face, decurved bill, and legs are a dull pink or orange. At the onset of breeding the soft parts become deep scarlet, with the exception of the distal 1/3 of the bill, which appears black on some individuals. The female at this time also develops a swollen gular pouch to a much greater degree than the male (Plate 1). This structure, along with the intense coloration, rapidly disappears after pair formation. The male has a longer bill than the female, a feature which aids in sexual identification at all times of the year (initial sexual identity was determined behaviorally). Palmer (1962) reports mean bill lengths of 153.3 mm and 124 mm for seven males and nine females, respectively.

The preening movements of the storks, as illustrated by the

Marabou (Leptoptilos crumeniferous) (Kahl, 1966) and those of the Green Heron (Butorides virescens), as described by Meyerriecks (1960), closely resemble that of the White Ibis. The following preening activities are most common for the White Ibis. The breast and ventral surface of the neck are preened by extending the neck up and out while pointing the bill downward, bringing it in contact with the feathers. The bill is then moved from side to side over the feathers,or opened and closed rapidly over the feathers of a particular area. Typically, the neck


14




15




feathers are extended during this motion. With the wing held loosely away from the side of the body, the ibis preens along its outer edge with a smooth stroke directed posteriorly. With the wings similarly positioned the bill is brought over the shoulder and pointed vertically downward to preen the under surface of the wing. The back is preened by merely turning the head posteriorly and erecting the back feathers. The abdominal region and ventral tail feathers are preened by bending the head down and reaching between the legs with the bill.

The bill is rubbed against the oil gland at the base of the tail and subsequently the bill and the side of the head are rubbed along the back feathers. This action often grades into rolling of the head from side to side while keeping it in contact with the back. During preening activity the head is often shaken from side to side with the bill pointing vertically downward. This head shaking motion is typically followed by preening of the ventral surface of the body. Feather ruffling is performed following a preening bout or, less frequently, from a motionless roosting posture. The wings are held away from the sides and alternately shaken up and down, with simultaneous erection of the back and neck feathers. Finally, the head and neck are shaken rapidly.

The ibis scratches directly over the wing with the longest toe. The head is lowered and cocked to bring the area to be attended into position.

Two types of stretching are common. The wing and leg of the same side are extended downward and posteriorly, or, both wings are cocked over the back while the head and neck are extended out and downward.













RESULTS


The Season


The breeding season of the White Ibis in central Florida

extends from as early as mid-March until the end of August, by which time all of the young birds are fully independent of the parents. Table 1 shows the dates for first occurrence of several key events for each year of the study at both of the study areas, and Table 2 pinpoints precise dates for 12 nests on Biven's Arm in 1973. Table 3 shows the mean ambient temperatures at the Apalachicola weather station for January through April in the years the study was conducted, and the date of the first observed copulation for each year.


Numerical Increase on Sea Horse Key


The early increase in White Ibis numbers in March is apparent on the island from late afternoon until nightfall. Most birds leave the island at dawn in the direction of the mainland and its extensive marshlands. At 1500 hours flocks begin returning to the island and continue to do so until nightfall. The number of birds that returns at this time increases steadily for at least two weeks prior to any actual breeding activity. Figure 3 shows the pattern of numerical increase for a day during this period prior to pair formation (14 March 1974).



16





17







Table I. Dates of first occurrences of nesting events for both localities.



Sea Horse Biven's Arm 1971 1972 1973 1974 1973 1974 First signs of
numerical increase 3 Mar 10 Mar 19 Mar 12 Mar -First copulation 17 Apr 20 Mar 31 Mar 28 Mar 27 Apr -First egg -- 24 Mar 4 Apr -- 30 Apr 1 Apr* First young -- 15 Apr -- 23 Apr 21 May First young alone
at nest -- 26 Apr -- 4 May 31 May




*abandoned
--no data








Table 2. Dates of key nesting events for 12 specific nests on Biven's Arm (1973).


First Day Last Observed Egg Young
Nest of Pair Copulation Ist 2nd 3rd 1st 2nd 3rd
1 26 Apr 30 Apr 1 May 3 May 5 May 22 May 23 May ?

2 26 Apr 30 Apr 1 May 3 May 5 May 22 May 23 May ?
4 26 Apr ? 30 Apr 2 May 4 May 20 May 21 May 22 May

6 11 Jun 14 Jun 15 Jun 18 Jun -- 6 Jul ? -7 11 Jun ? 15 Jun 17 Jun -- 5 Jul 7 Jul -8 11 Jun ? 15 Jun 17 Jun 19 Jun 5 Jul 8 Jul ?
9 11 Jun 15 Jun 16 Jun 18 Jun ? N. H N. H. N. H. 13 11 Jun ? ? ? ? ? ? 18 11 Jun ? ? 15 Jun ? ? ? ? 20 11 Jun 14 Jun 15 Jun 17 Jun ? 6 Jul ? ? 30 11 Jun ? 16 Jun 18 Jun ? N. H. N. H. N. H. 10 11 Jun 15 Jun ? ? ? ? ?

--not laid
N. H. not hatched
? date unknown







Table 3. Mean ambient temperatures for the months preceeding breeding. Date of the first observed copulation and the mean temperature for the 6 days preceeding it are also given. Climatic data in oF are courtesy of the U. S. Department of Commerce, Natural Oceanic and Atmospheric Administration (Apalachicola Station).

6 Days Date of
Before First First
Year Jan. Feb. 1-14 Feb. 15-28 Mar. 1-15 Mar. 16-31 Apr. 1-15 Copulation Copulation

1971 53.8 49.2 59.8 57.1 59.3 63.1 67.3 17 Apr

1972 58.6 51.4 58.4 59.6 64.6 67.9 64.7 20 Mar

1973 55.0 53.4 52.8 66.3 62.9 63.5 64.2 31 Mar

1974 65.6 59.1 55.1 65.8 61.9 68.2 63.0 28 Mar





900 800 700 600 500


m 400 S300


200


100



1500 1530 1600 1630 1700 1730 1800 1830 1900 1930
Hours
C1
o
Figure 3. The number of ibises arriving on Sea Horse through the day during the initial
numerical buildup. 14 March 1974.




21




Whereas single individuals fly to and from the island, flocks

of four to 20 birds are most common. During the evening returns early in the season flocks of 200 individuals are not uncommon. The ibises often fly in a Vee formation with individuals equally spaced, but this structure is quite flexible and changes in a few seconds to an undulating straight line either parallel or perpendicular to the direction of flight. Figure 4 illustrates the changing profile of a returning flock sketched from movie film. The ibises glide frequently and often a wave of gliding will pass down a column. As a line of birds moves it encounters local air currents and updrafts, creating undulations like a ribbon in the wind.

All flocks arriving early in the season fly to the western end

of the island and roost there. Bare mangrove branches in close proximity to other roosting birds are the most popular sites. Figure 5 shows the island with its principal approach routes and roosting areas employed during this period. At dawn the birds fly either directly to the mainland from the western end of the island or east across the island and off its eastern end. The first indication of the onset of breeding occurs when several hundred of these individuals fail to leave at dawn.


Aggression


The behavior of individuals that return for the commencement of breeding activities is noticeably altered. Many do not show characteristic headlong flight but, rather, fly with their bills pointed downward (examining the vegetation?). Loose flocks land periodically, roost briefly, and depart. At this time there is virtually no site attach-




22






Sections. Time scale appears on left (n cond




0



























5









Figure 4. Changing profile of a linear ibis flock, broken into two
sections. Time scale appears on left (n 100). Sketched
from super 8 mm movie film. Picture taken from Sea
Horse of flock returning from the mainland.










R = main roosting Scale
areas
(arrows indicate 0 feet 446 approach routes)




R R
















Figure 5. Approach routes of returning flocks as indicated by arrows and principal roosting
areas. (modified from Wharton, 1958).




24




ment, overt regression is minimal, and mobility is high. Passive displacement, the departure of one bird when another lands nearby, is the most noticeable form of interaction.

By noon of the first day some males select sites from which they will display and on which the nest will be constructed. As attachment to this single site increases, aggression toward intruders becomes more pronounced. Initially males are aggressive toward any individual that approaches within six to 10 feet. Aggressive behavior takes one of the following forms.

Forward Threat (after Meyerriecks, 1960, for the Green Heron,

Butorides virescens, and Kahl, 1966, for the Marabou Stork, Leptoptilos crmeniferus). Active displacement is accomplished by walking or flying toward an intruder with the body horizontal and the neck extended in the Forward Threat posture (Plate 2a). In most instances this approach results in flight, with the intruder turning his back to the attacker, compressing the body plumage and lowering the head (Plate 4a), and walking or flying off. This is less likely to occur if the other individual is also a resident male with some site affinity.

Stab-and-counterstab (after Blaker, 1969, for the Cattle Egret). If the intruder does not retreat, the attacker recoils his neck, raises the bill above the horizontal, and begins thrusting the head outward, striking with the gaped, pointed bill. These aggressive males consistently show erection of the scapular feathers. If the intruder at this point is equally tenacious he faces the attacker, assumes a similar recoiled posture (Plate 3a) and also begins bill





25




thrusting. Usually such a bout will take the form of a Stab-andcounterstab ritual in which male A thrusts toward the head of male B, while the latter is simultaneously retracting his neck (Plate 3b); then the process is reversed. This usually results in little physical contact and continues until one of the combatants turns away or begins fighting.

Fighting. When individuals are highly motivated, for example, during the initial encounter between neighboring males or an unmated male's first attack of an approaching female, the Stab-and-counterstab is not demonstrated. At these times aggressive individuals strike independently at the opponent, frequently biting the head and neck. It is only during this type of bout that injuries are a likely possibility. Bill thrusts are performed in 0.3 seconds (n = 33; s = 0.06).

In violent bill-thrusting bouts at the nest site, the resident male attempts to move into a position above the intruder and direct his thrusts downward. This is accomplished by climbing upward or by actually mounting the intruder. This latter behavior occurs only if the intruder is a female.

Aerial Aggression. Whereas several of the herons exhibit aggressive, extended pursuit flights during this early period (Meyerriecks, 1960), the male White Ibis never travels more than 10 to 15 feet to repulse an intruder and, once the intruder takes flight, the resident male returns to his display site. Aerial combat in this species is rare, seen only as a result of apparent accidents in the timing of displacement attempts. On three occasions males 10 to 15 feet




26




apart flew toward each other simultaneously in apparent mutual displacement attempts. The result was a mid-air collision in all three cases with single bill thrusts exchanged, followed by landing and turning away by one of the combatants.

Female Aggression. Females demonstrate the same postures, movements, and feather erection as males, but less readily. Lone females confine their attacks to other females exclusively and administer bill thrusts to males only when mated and on the nest site. Even under these conditions intersexual female aggression is rare in the absence of her mate. Intrasexual female aggression is most common during pair formation when females, attracted by the same male, land close to each other.

Pair Formation


Once a male has succeeded in establishing himself on a display site, he begins the performance of pair formation activities. All displaying is conducted at this site and, when displaying, he is mobile only in the pursuit of an intruder. The following are the principal activities of pair-forming individuals.

Snap Display (after Meyerriecks, 1960, for the Green Heron;

Kahl, 1966, uses this terminology for a different behavior pattern of the Marabou Stork). The unmated male White Ibis performs one conspicuous advertising display, the Snap. The male, from a stationary position, crouches and simultaneously extends the head and neck out and downward (Plate 4b). At the apex of the display he may close the slightly gaped mandibles over a twig and shake it briefly (occurred in




27



18.7% of the displays; 94 of 503). The wings are cocked over the back (occurred in 43.6% of the displays; 289 of 663) or held at the sides during the neck extension. The male then assumes a normal roosting posture. The entire display is performed in 1.1 seconds (n = 35; s = 0.09). Table 4 gives frequencies of performance of the principal pair formation activities, including the Snap. The male performs as many as 25 Snaps/min at the height of display intensity, with a mean of 6.5 (n = 1604; s = 4.4). He rotates his body constantly and displays in all directions, never showing any prolonged orientation toward any particular female in his area. The position of the scapular feathers is variable during the performance of the Snap, from completely compressed to fully erected.

A displaying male directs the neck extensions of the Snap downward at approximately a 450 angle unless there is another pair within three feet. The male then directs all extensions toward the pair when facing it. These Snaps are performed with the wings cocked and the scapular feathers erected, and they are performed more rapidly (0.67 sec; n = 4; s = 0.05).

Head Bobbing (new terminology). Head Bobbing, which appears

as a Snap minus a full neck extension, is also performed by displaying males. It consists of a dipping motion of the head while the neck remains retracted. It was performed at a rate of 3.7/min by the three males for which it was quantified (n = 214; s = 2.4) as compared to a snap rate of 5.9/ min for the same males. While Head Bobbing, the males did not extend their wings or show associated twig pulling.








Table 4. Pair formation activities of 15 males and 25 females. These are composite
data for all years at both sites. Data collected throughout the day, from
as early as 21 March until as late as 10 June.

Male Female No. No. Activity Nol/mi n. Range s Displays No/mi n. Range s Displays Snap* 6.5 0-25 4.4 1604 -- -- -- -Head Roll 1.5 0-6 1.4 430 3.8 1-13 2.5 404 Display Preen 2.5 0-8 1.5 157 2.2 0-6 1.5 160 Preen 3.2 0-13 1.7 901 3.5 0-12 1.9 404 Feather Ruffle 0.96 0-4 0.7 62 1.1 0-4 0.75 40 Head Bob 3.7 0-8 2.4 214 -- -- -- -* % with wing extensions 42.2 (n = 280 displays of 663)
% with twig pulling 18.7 (n = 94 displays of 503)







Pc3




29



Two of these three males abandoned their display sites within two hours after I began observing them.

Only unpaired males perform the Snap and Head Bobbing. All

other pair formation activities by both sexes are apparently intact or slightly modified preening movements, with only the frequencies of performance altered.

Head Rolling (new terminology). Head Rolling is performed

by both sexes during pair formation and is the dominant activity of unpaired females searching for a mate. The bird orients its bill horizontally and perpendicular to the body. The side of the head is laid against the back feathers. From this position the head is rolled, raising the bill above the horizontal. The bill may be carried a full 1800, through the vertical, to the other side, or as little as 300. A normal roosting posture can be assumed after one roll, or the head may be rolled back and forth for several seconds. A single roll takes 1.1 seconds to perform (n = 21, s = 0.31). Plate 5a shows an example of bill orientation when it passes through the vertical position. The male performs this activity in temporal sequence with the Snap at a rate of 1.5/min (n = 430, s = 1.4). The female, in response to the Snap displays of the male, will land within 15 feet of him, face him directly, and perform the Head Roll at a rate of 3.8/min (n = 404; s = 2.5).

This behavior appears quite similar to the rolling movements

performed during head rubbing, the preening activity described earlier. There is little rubbing during the Head Roll, however, and there is no temporal association between rolling and the oil extraction from uropygial gland, as there is during head rubbing.




30



Oriented as she is, the Head Roll of the female exposes her gular region to the male that she is watching.

Display Preen (after Kahl, 1972a, for Wood Storks, e.g.,

Mycteria americana; similar to the Wing Touch described by Blaker, 1968, for the Cattle Egret). During Display Preening, the bird runs its bill along the outside edge of the wing, with the wing held briefly away from the side. It appears as normal preening except that the bill is often out of contact with the wing feathers. The pair-forming male shows this behavior 2.5 times/min (n = 157; s = 1.5) and the pair-forming female 2.2 times/min (n = 160; s = 1.5).

Preening and Feather Ruffling. As shown in Table 4, both

male and female perform preening and feather ruffling intermittently with the above behaviors. Displaying birds are moving constantly and rates of performance for these movements are high when compared to rates for roosting birds not forming pairs. These latter individuals preen briefly, usually for less than one minute, followed by long periods of inactivity. Incubating birds, for example, execute a mean number of 2.6 preening episodes/hour. Males that begin displaying in an area and are not approached by any females within one to two hours discontinue this intense activity and then abandon the site. The rates of performance of displays differ from year to year on Sea Horse and between Sea Horse and Biven's Arm. Table 5 shows some of these data.

Table 6 gives a sequential analysis of the main activities of the male and female during active displaying. All activities were recorded simultaneously to determine possible cause and effect.







Table 5. Rates of performance of male pair formation activities (15 males total);
comparison of each year and both sites.


Head
Year Location Snaps* E n Rolls* s n Preen s n 1972 S. H. 10.7 5.7 405 1.6 -- 100 1.4 -- 94 1973 S. H. 4.9 3.1 605 0.81 -- 129 3.3 -- 526 1974 S. H. 5.8 3.2 338 2.2 -- 145 3.0 -- 195 1973 B. A. 7.5 5.3 256 1.5 -- 56 2.8 -- 86 Overall 6.5 4.4 1604 1.5 1.4 431 3.2 1.7 901


*NbJmin












CA





32



relationships between pair formation behaviors. The female Head Roll was preceded by the male Snap 27.2% of the time, the male Head Roll 3.8%, preening 36.1% and inactivity 19.6%. The Snap of the male was preceded by the female Head Roll 25.0% of the time, female preening 22.6%, and inactivity 41.8%. The male Head Roll was preceded by the female Head Roll 23.7% of the time, female preening 13.1%, and inactivity 55.3%.

Female Approach Attempts. Once a female has located a

male and has performed Head Rolling near him, she attempts to land next to him on his display site. She flies with her neck extended downward and her body contour feathers compressed, and crouches low upon landing. Initial approaches of this type are usually opposed by the male, for he immediately administers bill thrusts to the head and neck of the female. She flees, usually to her original perch, and the male immediately begins to Snap again (an action that is discontinued as soon as the female arrives). On Sea Horse as many as six females have been observed surrounding a displaying male and approaching in this fashion. The maximum number observed on Biven's Arm was two. The female returns to the male after a mean duration of 5.7 minutes (n = 44), and after several approaches begins to leave more reluctantly. Initially this hesitancy increases the male's aggression and the female is forced to flee.

Up-Down Greeting (after Kahl, 1972c, for the Openbilled

Storks, e.g., Anastomus oscitans). Acceptance of the female by the male is indicated by the Up-Down greeting display. As the female approaches with her head down, the male raises his head and neck, gapes








Table 6. Temporal relationships of main pair formation activities between male and
female.


Activity of Opposite Sex
Snap Head Roll Preen Inactivity Other Behavior Relationship No. % No. % No. % No. % No. % dSnap Following -- -- 43 25.0 39 22.6 72 41.8 18 10.6 cHead Roll Following -- -- 9 23.7 5 13.1 21 55.3 3 7.9 ?Head Roll Following 43 27.2 3.8 57 36.1 31 19.6 21 13.3 dSnap Followed by -- -- 45 26.6 43 25.4 67 39.6 14 8.4 dHead Roll Followed by -- -- 8 21.1 9 23.7 20 52.7 1 2.5 9Head Roll Followed by 38 24.0 9 5.7 59 37.3 32 20.2 20. 12.6 dSnap Simultaneous with -- -- 19 11.5 17 10.1 124 73.1 9 5.3 dHead Roll Simultaneous with -- -- 7 17.5 4 10.0 27 67.5 2 5.0 ?Head Roll Simultaneous with 24 15.3 8 5.1 40 25.4 70 44.6 15 9.6




34



his bill, and instead of thrusting downward, slowly arches his neck through 900 to a vertically downward position, simultaneously giving a soft honking vocalization. He may lower his bill next to the female's, or he may extend the arch over her, resulting in crossed necks. The female, still holding her head low, may remain motionless or join in by also arching the neck from the horizontal to the vertical with the male. Often brief twig pulling with lateral bill movements occurs as the bills reach the vertical position, especially in later greetings by the pair. The pitch of the vocalizations given during this ceremony are variable from the low "honk" of the male to the high-pitched scream of the female.

Four males demonstrated the transitional behavior involved in the change from rejection to acceptance of the female attempting to pair. Due to the female's crouched posture, the blows to her head are directed downward and the bill thrusts are administered with typically rapid pumping motions. For these four males, the females left less readily after several approaches and each had to attack more vigorously. The first indication of their acceptance of the female was a redirecting of the bill thrust adjacent to the female's head rather than at it. At the end of these thrusts each male showed twig shaking with lateral bill movements. Initially these redirected attacks were interspersed with actual blows to the female's head. The next step in the acceptance process was a reduction in the speed of the redirected thrust as the males began arching their necks over that of the female. Not all males demonstrated this transition from pure aggression to greeting. In 11 of 15 cases the male simply switched from one to the other in temporal sequence.




35



Mutual twig pulling with lateral bill shaking similar to that performed at the end of the Up-Down display is performed in several situations by the mated pair. It is seen following a nest disturbance (for example, following a bill thrusting bout with a neighboring pair), as a pre-copulatory activity, or without any apparent external stimulus as the pair stands together at the nest site.
Male acceptance of the female when she approaches is not necessarily an indication of pair formation. Once accepted, the female may be driven off subsequently (29 of 60 observed cases) or she may depart without provocation (31 of 60 observed cases). Table 7 gives the behavior of the males for 80 approaches by the females including initial reaction and behavior immediately prior to the female's departure. Prediction of probable pair formation is difficult until the performance of the first copulation. Of 15 pair formations observed, only two males showed the Snap display after their initial copulation (i.e., 13 of 15 no longer performed pair formation displays).

The performance of the above behaviors results in a high

level of activity for pair-forming individuals, and this level is reduced following the first copulation. One typical Biven's Arm pair averaged 10.5 and 12.8 activities/min for the male and female, respecitvely, during the five minutes preceding the first copulation, and

3.7 and 5.7 activities/min immediately after.

Whereas the nest generally is constructed at the site of pair

formation, 20% (3 of 15) of the pairs abandoned this area after pairing. Also, birds appeared in the study areas already paired, further indicating some mobility following formation. The stimuli for this movement are unknown.





36







Table 7. Initial behavior of displaying male when female
approaches and immediately prior to her departure.

c Behavior Prior
Initial ac Behavior n to ? Departure n

(-)* Bill thrust 20 (-) Bill thrust 18
(+) Inactivity 2

(+) Greeting 50 (-) Bill thrust 23
(+) Inactivity 20
(-) Other 7

(+) Inactivity 10 (-) Bill thrust 6
(+) Inactivity 2
(+) Twig pulling 2


C-) Totals 20 () 18 (90.0%)
(+) 2 (10.0%)

(+) Totals 60 (-) 29 (48.3%)
(+) 31 (51.7%)



+ denotes acceptance
- denotes rejection





37



Detailed observations were discontinued at nightfall, but

extensive vocalizations and wing flapping were audible throughout the night and indicate that at least greetings at the nest site were taking place at night during the pair formation period.

Whereas flocks of feeding ibises are a common sight at low tide on Sea Horse Key, a unique phenomenon occurs during the first few days of pair formation. In 1971 on the south shore, and in 1972, 1973, and 1974 in the basin on the island's north side, flocks of 20 to 100 individuals were observed standing in three to five inches of water, with less than 10% of the birds feeding (and, more commonly, with no birds feeding) (Plate 6a). These flocks were open with recruits arriving and residents departing every few seconds. Arriving birds invariably landed within three feet of another individual, but the latter showed no reaction. Occasional single bill thrusts were seen between individuals that came within a foot of each other, but no extended aggression occurred. The principal activities of the birds were: (1) head dipping (approximately 6/min), which consisted of a lowering of the head into the water and then raising up, sending a wave of water over the back; in 25% of the cases (n = 72) this was accomplished by an initial extension of the neck out and downward, a behavior pattern strongly resembling the Snap; (2) head shaking (approximately 1/min) following the wetting process; (3) feather shaking (0.5/min) performed with the legs flexed, resulting in splashing water over the wings and back; (4) preening (2.0/min). An individual would typically arrive without incident, dip its head into the water one or more times, shake the feathers for 10 to 60 seconds, preen and depart. Most individuals




38



remained in the flock less than five minutes. These flocks formed during the pair formation period are stationary, unlike the mobile feeding flocks seen throughout the season, and they are never seen after the days of pair formation have passed. Both sexes are present.


Copulation

The copulation that marks pair formation, as well as subsequent

copulations, take place at the nest site. The pre-copulatory activities of both sexes are shown in Table 8.

The male and female stand at the nest site in close proximity, with the male above due to the female's crouched posture (Plate 6b). It is from this position that the male reaches over the female's neck, extends his bill vertically downward, and pulls briefly at a twig with lateral head movements (Plate 5b). The female responds by lowering her body and may also join the male in twig pulling. Typically, male mounts the female from this posture (Table 8). The female shows no apparent solicitation behavior and she is often motionless prior to the mount (Table 8).

The male mounts slowly from the side of the female, one leg at a time (Plate 7a), and usually adjusts his position (= treads) for a few seconds before beginning to lower himself onto the female's back. Erection of the scapular feathers by the male often occurs at this time, especially in the early copulations of the pair (Plate 7b). When mounted, the female retracts her head and neck and positions her bill vertically downward. As the male lowers his body, the female begins to cock her wings over her back, thereby cradling the male, and also








Table 8. Pre-copulatory activities, both sexes. The larger sample size for the
female is a result of closer observation of her at this time.

cPre-Copulatory Behavior 9Pre-Copulatory Behavior Year Locality Twig Pulling Inactive Preen Twig Pulling Inactive Preen 1971 Sea Horse 2 0 0 2 1 0 1972 Sea Horse 0 0 1 1 2 1 1973 Sea Horse 5 0 0 5 11 0 1973 Biven's Arm 8 1 0 8 9 0

Total 15 1 1 16 23 1

Per Cent 88.2 5.9 5.9 40.0 57.5 2.5




40




raises her tail dorso-laterally. The male extends his wings and depresses his tail ventrally as he descends, positioning his bill vertically next to the female's bill (Plate 8a). Once lowered, the male's depressed tail is pumped laterally and the cloacas are brought into proximity (Plate 8b). In the last 1 or 2 seconds of the act the male stops lateral tail pumping and pushes forward. By now his center of gravity has shifted posteriorly and his bill is behind the female's, although still in a vertical position. In the last second the female reaches back with her bill, gapes slightly, takes the male's bill in hers, and shakes it vigorously and audibly. The posture is shown in Plate 9a. The male then immediately dismounts and the post-copulatory activities quantified in Table 9 are performed.

Although most copulations proceed smoothly from the initial

mount, the male occasionally places one leg on the female's back and subsequently withdraws into a normal roosting posture. Such aborted mounts are the result of disturbance of neighboring birds, female lack of cooperation (shown by a head-up posture rather than crouching), male loss of balance, or, simply, apparent lack of sufficient motivation in the male. Males that repeatedly fail to complete the mounting process preen vigorously between attempts.

Copulations occur throughout the day, beginning shortly after dawn and extending until night fall. The rate of copulation is not constant for each hour in the day, however, as illustrated in Figure 6. The mean length of the intercopulatory interval is 73 minutes, but this interval is extremely variable (range = 11 to 191 minutes). Table 10 summarizes the data on the length of the interval as a function of







Table 9. Post-Copulatory Activities male and female.

cr Post-Copulatory Behavior 9 Post-Copulatory Behavior Year Locality Slight Preen Preen Inactive Other Slight Preen Preen Inactive Other 1971 Sea Horse 2 3 13 7 5 4 9 3 1972 Sea Horse 15 12 10 5 12 3 22 3 1973 Sea Horse 1 8 31 11 5 32 10 13 1973 Biven's Arm 3 7 18 1 5 10 8 4

Totals 21 30 72 24 27 49 49 23

Percent. 14.3 20.4 49.0 16.3 18.2 33.1 33.1 15.6








0.8


0.6 6(31.5)


0.6


0.5
0.5 (52) (28)
0(31)
0.4 (35)
a (47)
32) (39)
0. 0. 33.5) (
M- (37)
(31)
o 0.2


0.1



0600 0700 0800 0900 0100 1100 1200 1300 1400 1500 1600 1700 1800 Hours
Figure 6. Copulation rate per pair hour for each hour of the day. Data are composite from all years
in both localities. Within parentheses are the total number of pair hours of observations
at each time.




43




locality, lateness of the season, and day in the copulatory period (1 and 2 vs. 3, 4, and 5). The most intense period of copulatory activity occurred for Pair 3 on 6 April 1973 on Sea Horse (fourth day of copulation). Following two copulations with other males by the female at 1012 and 1026 hours, the pair copulated at 1033, 1048, 1100, 1145, 1210, 1308, and 1502.

Between copulations, the male of each pair gathers nest material and the female constructs the nest. During the male's absence from the nest site, neighboring males approach and attempt copulation with the unattended female.

In 330 pair-hours of observation of 26 pairs during the copulation phase, males attempted to mount females other than their mate 62 times. Of 26 known females 16 were approached by 15 of 26 males under observation and approximately seven unknown males. Of the 62 attempts only 12 were apparently successful (i.e., terminated after lateral tail pumping by the male and bill shaking by the female).

Only four of the 62 approaches met with even slight female

aggression. In each of these four instances, the female gave one slow bill thrust in the direction of the male. None of these actually struck and none was successful in discouraging the copulation attempt. All 50 unsuccessful attempts were thwarted by another male, 46 by the female's mate and four by another interloping male also trying to mount. The female assumed a motionless, slightly crouched posture similar to the normal pre-copulatory position 56 of the times she was approached. Twice females greeted interlopers with the Up-Down display in the same manner that they would their own mate. Males only approached females





44




Table 10. Intercopulatory intervals. The 63 values are grouped
as to locality, time of season and stage of the
copulation cycle.

Intercopulatory Interval (x min) Range n Locality

Sea Horse 75.5 11-191 54 Biven's Arm 59.7 22-124 9 Time of Season

Early 80.0 11-186 43 Late 58.3 21-191 20 Overall 73.2 63 Stage of Copulation

1-2 days 65.9 21-140 32 3-4-5 days 77.9 11-191 31




45




alone on a nest site and no male traveled more than 15 feet to attempt copulation. All 15 promiscuous males known to me were already paired, as were all 16 females. While 15 males were observed in the pair formation period, none was ever seen approaching nearby paired females. The most promiscuous female copulated with her mate 63% of the time (7 of 11), followed by a female who did so 85% of the time (17 of 20).

The female continues to return to the nest site with her neck extended and head down throughout the copulation period.

The duration of the greeting display is reduced by the second

day of copulation, as the males frequently arrive and depart with nest material. Vocalizations become more brief, and often are not given at all. By the fourth day of copulation and thereafter, the greeting display is reserved for the return of one of the pair following an extended absence from the nest. By this time also, the sexual difference in the pitch of the vocalizations given by each sex during the greeting has disappeared.

On Sea Horse, the female leaves the nest site for several hours on the third or fourth day of copulation apparently to feed, as some are observed flying toward the mainland. During the female's absence, the male usually remains at the nest site. Infrequent departures by the male occur, and at these times any construction already completed at the nest site is in jeopardy. Biven's Arm males never leave the nest unguarded at this time. When the female returns to Sea Horse, she remains at the nest site until the first egg is laid on the fifth day of copulation, performing her duties as primary nest builder. The




46




females on Biven's Arm leave the nest site on day three as well but, unlike the Sea Horse females, they may feed two or more times by the laying of their first egg.

Early in the copulation period vocalizations are audible at

night but wing flapping is much less evident than during pair formation. Spot checks indicated that most pairs spend the night together at the nest site, with approximately 15% of the pairs represented by only one member after dark.

Allopreening was observed 10 times in the four years of data

collection, all 10 occurring during the copulation period. Performance of preening was divided evenly between males and females (five each). Allopreening occurred both before and after copulation and during periods of nest material collection by the male, apparently independent of copulatory behavior. Participating pairs ranged from newly formed to four days old. In all cases the dorsal surfaces (the back and neck) were the target areas.

Very few copulations occur after the first egg appears on the fifth day of copulation.


Nest Building


Nesting begins on different parts of Sea Horse over several weeks. Pair formation is rarely performed by a single couple at a given location but, rather, by clusters of five to 20 pairs all synchronized within 24 hours of each other and clumped together spatially.

The island is not settled randomly. The earliest pairs each year nest on the western side of the island, (Area 1, Figure 7).




47




Subsequent pairs form east of this point until they reach the clearing in the center of the island (Area 2). Pairs then nest on the eastern side of the island just beyond the clearing (Area 3), and not on the edge of it, as might be expected. The birds then converge on the clearing from east and west (Area 4). Finally, nest sites are selected on the extreme eastern end of the hammock, in the isolated stand of trees in the northeast section of the island, and in the trees bordering the south beach (Area 5). In nesting seasons with fewer pairs nesting, such as 1971 and 1974, Area 5 is not used. Trees in Area 5 are exposed to the formidable onshore winds. The trees in the principal study area (Area 4) are used every year. The ibises do not nest in the well-developed stands of black mangrove which occur along the northern shore of the island around the border of Sea Horse Creek or the entire Gardener's Arm area, the very sites selected by the herons and egrets. This segregation of the ibis from the herons is not seen on Biven's Arm. Here, the herons, egrets and the White Ibises all nest in close proximity and interact.

When the pair has been formed and copulation has begun, the male

alone begins to gather nest material. I never observed a female gathering nest material off the nest site or returning to the nest site with material. The first trips of the male when nest building begins are brief and often he returns without material. He gathers twigs first in the immediate area of the nest and nearby unattended sites, and then moves farther outward. On Sea Horse, although the thick vegetation prevented continuous observation of males, most collections apparently take place within 25 feet of the nest. These collecting trips are as









N Scale

0 feet 446









M






2 3 Figure 7. Order of settlement of nesting areas, numbered chronologically. Area 1 settled
first. Entire nesting area is hardwood hammock. (Modified from Wharton, 1958.)




49




brief as they are close to the nest, the mean duration of male absence from the nest when returning with a twig being 2.8 min (n = 127). Even when unsuccessful at obtaining any material, collecting males return to the nest every 4.2 min (n = 42).

At the height of nest building in an area any nest left unguarded is pirated, usually within 15 min if active males are present. Males visit abandoned sites repeatedly (as often as 17 times in 30 min) and whole nests can be disassembled in an afternoon. Throughout nest building activities, which continue well into incubation, the pair alternates absences from the nest. Males usually do not steal material from tended nests, although on two occasions on Sea Horse males from nearby nests have been observed pulling twigs from beneath an incubating female.

Males collecting nest material usually interact little with each other. Aggression occurs when two males simultaneously select the same twig. This was only observed on Sea Horse when males were on the ground and covering large areas in search of twigs. Interactions were brief. One male administered a bill thrust to the head of the other and the latter turned away and walked off. The first male to the twig was the aggressor in the few cases observed (n = 4). A single rasping vocalization accompanied the bill thrust in all four encounters. Males on the ground at Biven's Arm were almost impossible to observe, but they did show considerable movement and wing flapping, suggesting that, in the limited area in which they were collecting material, competition for twigs on the ground during nest building and aggression of the type described above may have been more pronounced than on Sea Horse.




50




In the clearing at Sea Horse males began searching on the ground for material on the third day of building. While known males collected twigs close to the nest in all observable areas, individuals were seen flying over the clearing with material in rare cases, indicating that collecting some distance from the nest does occur.

Males begin gathering materials at dawn and some males work until nightfall. Lack of audible wing flapping at night indicates that they discontinue this activity after dark.

The male grasps twigs firmly with the bill and employs a lateral or a push-pull motion in loosening them. Once freed in this manner the twig is adjusted in the bill until the male has grasped it firmly in the center. He then flies with it to the nest. Long or bulky twigs are occasionally dropped or get caught in the trees. Males typically show great perseverence in the pursuit of these problem twigs. One male that dropped a twig while roosting on a limb near its juncture to the trunk, reached out quickly with his leg and trapped the falling twig against the side of the tree. He then reached down with the bill, grasped the twig firmly, and returned with it to the nest.

When the male returns to the nest with material the female greets him with a brief Up-Down display. The male may simply place the twig down next to the female or, if it is small and easily managed, he may extend his head and neck over the female's and place the twig in that manner. In either case the female immediately seizes the twig and begins lateral bill shaking while slowly moving her head forward (the "tremble shove technique" of Meyerriecks, 1960). The male at this time may either release the twig immediately or perform tremble shove move-





51



ments with the female. The twig pulling at the end of the greeting display is now functional. The latter activity occurs most often with larger twigs in the initial stages of construction.

Table 11 shows quantitatively the division of labor for actual

construction of the nest. The data reveal that while the female is the principal builder the male makes a considerable contribution, assisting the female in placement of material in 27% of the cases observed (n = 165). Release of the twig by the male is followed either by his preening or departure for more material. Males that characteristically help the female very little still demonstrate twig pulling with her prior to copulation. Following copulation these males revert to merely dropping twigs on the nest and departing. Males continue supplying material through at least the first half of the incubation period. When relieved at the nest site by the female during incubation,the male collects for a time before departing for the feeding grounds. Males have been observed returning up to 15 times with material before leaving to feed. The female always departs immediately for the feeding grounds when relieved.

Males show considerable variation in the timing of their gathering efforts. Some begin collecting twigs immediately after pair formation and, with the females, build a considerable structure by the third day of copulation. Others collect very little until the third or fourth day of copulation and then work intensively for 24 to 48 hours, completing a structure sufficient to hold the first egg on day five. This variation in the timing of nest building occurs on both Sea Horse and Biven's Arm.





52






Table 11. Division of labor for twig placement following male
return with nest material.


dcad 9
Locality Year 9 Only* 9 Predominately Equally Sea Horse 1971 3 0 4 1972 32 40 8 1973 16 15 17 Biven's Arm 1973 12 3 15 Total 63 58 44 Percent. 38.2 35.2 26.6



*males never placed twigs alone




53




Nests were painted prior to the breeding season in the clearing on Sea Horse in 1972. Of 25 painted nests, 22 were completely disassembled so that only the painted branch upon which they were constructed the previous year remained. The remaining three were built upon and used during the 1972 season. Along the south shore 25 nests were also painted but the entire area was unused.

Over two winters 1000 nests were examined on Sea Horse and a variety of parameters measured. Similar data were collected for all available nests on Biven's Arm. Table 12 shows mean values and standard deviations for nest heights, diameters, and nearest neighbors for the two areas. Table 13 shows the percentages of nests in the various tree species for both areas and the percentage of the total flora each species constitutes. On Sea Horse the development of the vegetation beneath the nests is extremely variable, ranging from a dense tangle of vines to complete absence of flora. The branches upon which the nests are constructed ranged from under 1/4 inch (for the clusters of vines in which nests were found 8.6% of the time) to over three inches in diameter (for the oak trees). Since the Biven's Arm birds nest in only two species of trees, there is less variation here.

When local clusters of nests are considered on Sea Horse, however, the variations in height, diameter, tree species, and nature of the vegetation beneath the nest are much lower. Tables 14 and 15 show the mean values and standard deviations for the nest height and diameter within each cluster, and the species of tree in which each cluster occurred. In all 44 clusters the standard deviation of the height is less than the overall value, and in 37 of the 44 clusters the standard deviation of the




54









Table 12. Nest site data. Overall values for Sea Horse
Key and Biven's Arm for nest height, diameter,
and nearest neighbor.





Sea Horse Biven's Arm Nest Parameter Mean s n Mean s n Height 12.0 ft. 5.3 999 5.9 ft. 1.9 83 Diameter 10.0 in. 1.9 1051 10.1 in. 1.2 78 Nearest Neighbor 3.8 ft. 3.7 1052 1.8 ft. 1.4 72




55






Table 13. Data on nesting trees. Number and per cent of nests
in each species and number and per cent of each species
in hammock on Sea Horse.


Trees in x Nesting Nest Nests in % Areas % Height Species* n Total n Total (feet) Sea Horse:

Tamala littoralis (Bay) 706 67.1 154 36.0 11.6 Quercus virginiana (Oaks) 128 12.2 111 25.9 18.0 Quercus laurifo ia

Sabina siZicicola (Cedar) 44 4.2 45 10.5 11.26 Sabal palmetto (Palm) 42 4.0 89 20.8 14.19 IZex vomitoria (Yaupon) 41 3.9 29 6.8 5.93

"vines" 91 8.6 -- -- -Biven's Arm:

Sambucus canadensis (elder) 61 85.9 Acer rubrum (Red Maple) 10 14.1



*species names from Wharton (1958)




56


Table 14. The mean and standard deviation (s) of nest heights
for clusters of synchronized nest and overall values.

x
N in Height Species* Cluster (Feet) s

Bay 5 8.7 0.27 10 5.6 1.40 10 6.8 1.43 13 10.9 1.50 11 10.1 1.58 17 6.1 1.66 12 9.5 1.82 6 16.3 1.86 6 18.5 1.97 7 12.3 2.06 15 14.8 2.24 12 9.8 2.45 9 15.0 2.65 12 13.2 2.67 7 13.4 2.70 9 12.4 3.20 8 11.0 3.25 9 11.4 3.50 9 16.4 3.84 Cedar 5 9.4 0.97 6 10.0 1.90 3 18.0 2.00 7 12.7 2.69 Oak 7 15.2 0.75 7 36.9 1.46 4 9.8 1.50 9 15.4 2.30 5 26.0 2.55 6 19.0 3.10 6 21.3 3.38 5 14.0 3.46 Palm 4 10.0 0.00 5 16.0 0.00 3 17.0 0.00 3 18.0 0.00 3 19.3 1.15 4 15.5 1.73 Yaupon 3 9.0 0.00 3 7.3 0.58 8 3.4 0.73 4 5.6 0.75 7 4.4 0.96 6 3.0 1.00 4 7.0 1.15 All trees in study 999 12.0 5.29

*data arranged in order of increasing s for each species




57


Table 15. Mean and standard deviation (s) of nest diameters
for clusters of synchronized nests and overall values.

x
N in Diameter Species Cluster (inches) s
Bay 6 9.3 0.82 12 9.2 0.87 15 11.1 1.03 9 12.1 1.05 11 9.2 1.08 13 9.1 1.11 7 10.6 1.13 10 10.0 1.15 6 9.7 1.21 12 8.6 1.29 5 9.2 1.30 9 10.2 1.30 7 9.4 1.40 12 10.9 1.51 9 9.8 1.56 17 9.4 1.58 8 9.9 1.73 10 9.4 1.84 9 10.4 2.07 Cedar 7 9.1 1.57 5 10.0 1.59 6 9.8 2.23 3 10.7 2.89
Oak 5 9.0 0.71 6 9.3 0.67 5 10.4 1.14 6 10.5 1.17 4 10.2 1.26 9 9.2 1.30 7 10.2 2.57 7 12.6 2.76 Palm 4 13.8 0.50 4 9.2 0.95 5 13.2 1.10 3 10.7 1.15 3 12.0 2.00 3 9.7 2.08 Yaupon 4 7.8 0.50 6 9.7 0.52 3 7.7 0.58 3 9.3 0.58 4 9.0 0.82 8 8.4 1.19 7 9.1 1.68 All trees in study 1051 10.0 1.89

*data arranged in order of increasing s for each species.




58




diameter is less than the overall value, illustrating the comparative similarities of these parameters for the nest sites in the clusters. Also, all of the nests of a cluster have a similar understory and accessibility, and are composed of similar materials. Because all of the nests are within a 25-foot radius, the pairs probably experience similar wind velocities and predation pressures as well. No isolated nests were observed on Sea Horse, and only four such nests were observed on Biven's Arm.

The nest itself is constructed entirely of twigs up to three feet in length and one inch in diameter, with the larger twigs forming the basic framework and the smaller twigs the cup. The final addition to the nest is a lining of leaves or Spanish moss. The leaves used are from the immediate vicinity of the nest, further indicating the local nature of nest material collection.


Egg Laying

The female lays the first egg on the fifth day after the beginning of copulation. Incubation prior to completion of the clutch occurs infrequently on both Sea Horse and Biven's Arm. The second egg is laid two days later and the third egg (on Biven's Arm) laid two days after the second (see Table 2). Table 16 gives clutch sizes for several years on both Sea Horse and Biven's Arm. In every year the mean clutch size on Sea Horse was < 2.2 eggs per nest whereas at Biven's Arm it was always > 2.8 early in the season. The mean clutch size late in the season at Biven's Arm dropped to < 2.2, however. Table 16 also gives data for clutch sizes for various populations of White Ibis from the







Table 16. Clutch size data for Sea Horse and Biven's Arm, and from inland Florida sites
(from the Florida State Museum egg collection).
Size of Clutch
One Two Three Four Locality Season Egg Egg Egg Egg x

Sea Horse 1971 0 6 0 0 2.00 1972 4 42 14 0 2.17 1973 8 51 13 0 2.07 1974 7 56 7 0 2.00 Overall 19 155 34 0 2.07

Biven's Arm Early 1973 0 2 20 0 2.91 Late 1973 3 24 9 0 2.16 Early 1974 0 3 13 0 2.81 Early overall 0 5 33 0 2.87 Late overall 3 24 9 0 2.16

Inland Florida sites* 1926 0 3 17 5 3.12 1928 0 2 9 0 2.82 1929 0 0 10 3 3.23 Overall 0 5 36 8 3.08


*from museum





k,




60




egg collection of the Florida State Museum. For all of these inland populations the mean clutch size was > 2.8.

Between the laying of each egg, the female feeds while the male tends the nest, and it is at this time that the alternation of adults at the nest begins. This phenomenon occurs at both Sea Horse and Biven's Arm, but the intervals between exchanges at the nest are quite different (see Table 20).

Incubation


Consistent incubation begins with the completion of the clutch. Figure 8 shows the relationship between the number of minutes off the nest (inattentiveness) and the time of day. On the same graph is a plot of the mean ambient temperature per hour interval, using only the days of relatively uniform temperature. Both lines assume an approximate bellshaped curve with maxima at 1500 hours. The smooth shape of the curve showing the number of minutes off the nest per hour is disrupted somewhat by the depressed value for the hour 1200 to 1300. As the graph indicates, all six pairs were shaded over more than 80% of their bodies at this time.

Figure 9 shows the mean number of minutes off the nest per hour for each day of observations. Days on which rain occurred and days on which observations were made only during the hours when temperatures were highest are indicated.

Table 17 gives values for the number of minutes off the nest

per pair for the block of time 1200 to 1500 hours for each sunny day in an effort to determine the change in attentiveness as the 21-day incubation period progresses. Time off the nest is low on day three of







13 minutes off eggs -34
o temperature
12 all adults in <20% sunlight o 33
11 32
o 32 100 o
31

9 '30
SL 0
o 8 29
0 .
7
28

06 o 27

S5 -26

4- 4
o o 25

3 '24

E 2
2 o o 23

1 -22


0500 0700 0900 1100 1300 1500 1700 1900 2100 Hours

Figure 8. Incubating adults number minutes off nest vs. time of day and oC vs. time of day.
Data are from sunny days of May 1971.






1000-1500 hrs only 10 ** 1030-1630 hrs only Rain
9 **


8 *

7



















Date (May) 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 Day of incubation 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20


Figure 9. Number of minutes off the eggs/por. hr of incubation vs. the day of incubation.




63





Table 17. Minutes off the eggs (inattentiveness) for the block
of time 1200-1500 hrs. Included here are data for the
warm and sunny days only (1971).


Total min. of
Day of Inattentiveness # of
Date Incubation 1200-1500 hrs. Pairs Pair 8 May 3 95 6 15.8 9 May 4 203 6 33.4 11 May 6 189 6 31.5 18 May 13 159 5 31.9 22 May 17 101 3 33.7 25 May 20 193 4 48.2




64




incubation (15.8 min per pair) and high on day 20 (48.2) but the days in between all show times within 2.2 min of each other (31.5 to 33.7).
Table 18 gives rates of performance for several activities during incubation. These values are actually the percentage of rises (times off the eggs) during which each behavior is performed and give no indication of the number of performances per rise. There is a general decline in activity levels from those of the pair formation period (Table 4). Incubating birds frequently turn their heads posteriorly and rest the bill on the back, covered by the back feathers. This behavior is most common in the early morning and in the rain, but is seen throughout the day, and rarely, in temporal sequence with gular fluttering.

Incubating birds exposed to direct sunlight often resort to

gular fluttering. The bill is gaped slightly and the throat oscillated

4.0 times per second. This rate is constant for all birds over seven days old and at all temperatures. The amplitude of the oscillations appears' to increase with temperature, however.

Rates of nest relief during incubation apparently reflect

distances traveled to obtain food and, in turn, determine the maximum rate of food delivery to the young when they hatch. On Sea Horse, exchanges occur once a day. During the intensive observations in 1972, 17 exchanges were recorded. All occurred between 1100 and 2000 with sexes alternating days on the nest. The individual being relieved at the nest may begin greeting vocalization when the mate is still 10-15 feet off. After the greeting the relieved bird departs within 30 seconds.










Table 18. Rate of performance of activities during incubation period. Included are rates overall, on rainy days, and on days on which data were collected during hot hours only.


No Times
Pair off the Feather
Hours eggs No Min. up Preen Twig Pull Ruffle Head Shake Tail Flick Stretch Scratch
(Pr. Hrs.) Pr. Hr. Pr. Hr. Pr. Hr. Pr. Hr. Pr. Hr. Pr. Hr. Pr. Hr. Pr. Hr. Pr. Hr.

Overall 365 3.5 6.9 2.6 1.9 0.20 0.12 0.26 0.24 0.56 Rainy Days 90 1.9 1.9 1.3 0.83 0.36 0.20 0.11 0.07 0.27 Sun Days 70 4.3 13.9 3.3 2.7 0.13 0.13 0.22. 0.29 0.71



*days when data were collected only during warmer hours (1100-1600).




66




While copulations between partners discontinue with the laying of the first egg, promiscuous mating occursin rare instances after this time (observed three times in four years). Of the four cases of bill thrusting by females toward approaching promiscuous males, three took place during these late attempts. After the third day of incubation no promiscuous mating attempts occur. Males still approach nearby incubating females but, instead of copulating, they pirate nest material. The female at this time greets interloping males with the Up-Down display but does not leave the nest, as she would if the approaching male were her partner.

The earliest case of shading behavior (dropping wings ventrally while standing over eggs) was recorded on the afternoon of the fourth day of incubation (at 1444 hours) with an ambient temperature of 34.00C, measured on the tower. The adult was fully exposed to the sun. Shading was next seen on the 15th day (at 1423) by one adult, again in direct sun. At 17 days all four adults observed showed shading in 330C temperatures (first at 1446), even with no individual fully exposed to sun. The posture is shown in Plate 9b.

Biven's Arm adults spend several minutes at a time as far as

10 feet from the nest when eggs or very small young are present. This behavior is extremely rare on Sea Horse.

The incubation period is 20-21 days (see dates in Table 2).

Daily visits to the nest were possible only on Biven's Arm, and here the young hatch two days apart. This asynchronous hatching indicates that the first egg begins to develop before the clutch is complete.




67



Behavior of Young

The young escape the egg by pecking a hole at one end of the egg (usually the blunt end). Adults were never observed assisting in the process, although when the young has emerged the adult removes the shell from the nest and discards it with a lateral bill shake. This same bill movement is seen throughout the cycle when debris falls into the nest itself. The behavior of the adults changes very little for the first day of the nestling's life; they rise, reach into the nest as if turning eggs, shake twigs, preen and sit precisely as before hatching.

In the first few days of life, the young ibises on Sea Horse are

susceptible to predation by Black-crowned Night Herons. On two occasions the herons were observed flying with young in their mouths, and their presence in the rookery is common. Adult ibises defend against intrusion by the Black-crowns with threat displays and actual bill thrusting if the heron attempts to land at the nest. Fish Crows also are capable of taking one-day old birds and their presence also alerts the adults.

One rather unusual predator destroyed my study site in 1971. An immature Bald Eagle landed among five nests, resulting in immediate flight by the adults. Of the seven young present (10 days old) two were killed outright, two fell to the ground and were lost, one was displaced from the nest five feet, and the others were unharmed.

The newborn ibis is covered with a soft black down, is blind, and for the first day is barely capable of raising its head. By the second day, however, the nestlings can raise up and accept food from




68



the parent. Until day seven all feeding is initiated by the adult that returns with a crop full of food, positions its bill vertically, and lightly grasps the bill of the young. This stimulates the young to raise its head upward, sliding the bill up to the mouth of the adult. At this point the adult gapes widely and the nestling's head literally disappears into the parent's mouth. There follows a series of head jerks as the food is regurgitated directly into the nestling's mouth (Plate 10b). The process of transfer takes from three to 10 seconds after the nestling's head is in position. Once fed initially the young begin issuing a begging call--a rapidly oscillating scream of one to two seconds in duration repeated as often as every two seconds. In the first days the bill is held horizontally and not oriented in any particular direction. The head bobs up and down as the nestling calls with the wings extended and fluttered simultaneously. At about seven days the young has grown large enough so that it can reach the bill of the adult when begging (Plate 10a). At this time the bill is no longer randomly oriented, but is aimed at the distal 1/3 of the adult's bill. The head bobbing now brings the tip of the young's bill into repeated contact with the adult's, stimulating the adult to move the bill to the vertically downward position and gape while the bill of the nestling slides up and into the adult's mouth. Feeding at seven days still takes between three and 10 seconds, with head jerking more pronounced than it is for newly hatched young.

The first young hatched is generally larger than his nestmate(s) and can reach higher during this active begging. The adult attempts to feed both by moving its bill away from the larger young once it has been




69




fed one or two times. If the size difference is great, however, the larger young often climbs over the smaller and succeeds in obtaining several consecutive feedings. In these cases the differences between young are augmented further. At times when the adult is attempting to feed the smallest young, both nestlings often reach for the adult's mouth simultaneously. This results in the abortion of the feeding attempt via the assumption of an erect posture by the adult; the nestlings then revert to the begging vocalization.

Returning adults do not all begin feeding the young immediately. A period of inactivity may precede the onset. If the young are large enough to reach the horizontal bill of the adult, the bill is often placed on the back and out of the nestlings' reach. This behavior also occurs when the adult has finished feeding the young but they continue to beg.

Up until approximately 10 days of age, the young locomote poorly and remain on the nest site, although they do climb onto immediately adjacent limbs. On two occasions five and seven-day-old young were accidentally displaced from their own nest by the parent and crawled into a neighboring one. In both cases they were fed along with the resident nestlings but subsequently returned to their own nests. Several young of ages 10-20 days were in a neighboring nest when the adult returned and these were immediately attacked and driven off. Young ibises at age 10 days move freely from nest to nest in an area but are fed only by their own parents. Individual recognition of young by parents apparently develops at the time the nestlings gain mobility.

Up until the age of 10 days parents continue to alternate at the

nest site. The young are fed by the returning parent intermittently for




70




an hour, with the majority of the feedings occurring in the first 15 minutes. Table 19 gives values for feedings/15 min interval and seconds/ feeding for both Sea Horse and Biven's Arm. Crows and Black-crowned Night Herons feed on very small young and the vigil by the parents afford the young some protection. At 10 days of age, however, both parents begin gathering food simultaneously leaving the young alone on the nest. For the next 10 to 14 days the young stay in close proximity to the nest but do visit neighboring sites, returning hurriedly to their own nest when a parent returns with food. Following feeding the parent leaves and the young continue their activities. It is during this period that the behavior of the young is most easily observed--they are large enough to see and yet too small to be excessively mobile.

All of the maintenance activities of the adults are performed by

the nestlings at this time; preening, leg and wing stretching, scratching, feather ruffling, twig pulling, and even bill thrusting and allopreening between nestmates. When alone at the nest the young seek shade during the afternoon hours. Strange adults arriving at the nest site may or may not elicit a response from the young. Ten-day-old young show both extremes from intensive begging to a crouched, motionless posture. If the young do beg from a strange adult they are attacked,whereas, if they lie still the adult is not aggressive.

Table 20 shows intervals between feedings for Sea Horse and Biven's Arm, and the resulting differences in seconds of feeding/day at each site are calculated in Table 21. Although the Sea Horse adults fed the nestlings more times per 15 min interval (18.2 versus 14.8 for Biven's Arm) and fed them longer at each feeding (4.8 versus 4.3 seconds for Biven's




71





Table 19. Feeding rates of young for Sea Horse and Biven's Arm.
Feedings/15 min interval and No.sec/feeding for young of two age groups.

Sea Horse

Age of
Young Total No. 15 min. Feedings No. sec. of No. Sec.
Date (Days) Feedings Intervals interval Feeding Feedings Feeding 1971 1-5 131 7 18.7 663.5 118 5.6
6-10 107 7 15.3 229.5 74 3.1 1972 1-5 98 6 16.3 350.5 92 3.8
6-10 272 11.4 23.9 957.5 201 4.8 1973 1-5 10 1 10.0 41.0 8 5.1
6-10 72 3 24.0 250.5 49 5.1 1974 1-5 17 3 5.7 54.5 10 5.4
6-10 58 4 14.5 235.0 47 5.0 Totals 1-5 256 17 15.0 1109.5 228 4.9
6-10 509 25 20.4 1742.5 370 4.7 Overall 765 42 18.2 2852.0 598 4.8













Table 19. Extended..

Biven's Arm

Total No.15 min. Feedings No. sec.of No. Sec. Feedings Intervals Interval Feeding Feedings Feeding






82 7 11.7 225.5 49 4.6 77 6 12.8 125.5 39 3.2 38 3 12.7 90,0 20 4.5 144 7 20.6 503.5 110 4.6 120 10 12.0 315.5 69 4.6 221 13 17.0 629.0 149 4.2 341 23 14.8 944.5 218 4.3








Table 20. Feeding intervals Sea Horse vs. Biven's Arm and Biven's Arm early vs. late in season
for young of two age groups.
Sea Horse Biven's Arm
Age of Total No. Min. Total No. Min.
Date Young Min. Intervals Interval Range Min. Intervals Interval Range 1971 1-5 662 2 331 233-929 -- -- -- -6-10 768 2 384 368-400 -- -- -- -1972 1-5 2046 5 409.2 338-489 -- -- -- -6-10 2207 5 441.4 350-510 -- -- -- -Early 1973 1-5 761 2 385.5 341-420 824 4' 206 173-230
6-10 -- -- -- -- 516 3 172 136-196 Late 1973 1-5 -- -- -- -- >1218 4 >304.5 -6-10 -- -- -- -- -- -- -- -Early 1974 1-5 -- -- -- -- 610 3 203.3 168-240
6-10 -- -- -- -- 853 5 170.6 118-225

Totals Early 1-5 3469 9 385.4 233-489 1434 7 204.9 168-240
6-10 2975 7 425.0 341-510 1369 8 171.1 136-225 Overall 6444 16 402.8 233-510 2803 15 186.7 136-240 Totals Late 1-5 -- -- -- -- >1218 4 >304.5 --









Table 21. Composite calculation of seconds of feeding/day at Sea Horse and Biven's Arm,
based on data from Tables 18 and 19.


Mean No. Sec.* Feedings* No. 15 min. Feedings Seconds Feeding
Locality Feeding 15 minutes Day Day Sea Horse 4.8 18.2 2 = 175 Biven's Arm 4.3 14.8 3.5 = 223



From Table 19.
tFrom intervals between feedings; the number of feedings possible through the day is approximated (also, on Sea Horse, two feedings/day is the observed maximum).




75




Arm), the Biven's Arm adults could provide approximately 27% more feeding time per day (224 versus 175 seconds for Sea Horse) by virtue of the shorter interval between visits (3.1 versus 6.7 hours for Sea Horse). Table 20 further shows the increase in the interval for Biven's Arm late in the season (up to 5.1 hours).

These tables, divided into data for young birds 1 to 5 days and 6 to 10 days old, also reveal changes in rates of feeding with age. Both Biven's Arm and Sea Horse adults fed the older young more often and at the same time, more quickly. The data for each year, however, reveal that these changes did not occur in all years.

Changes in the intervals between feeding visits with the age of

the young were opposite at the two sites. At Sea Horse in both 1971 and 1972 the interval increased with age, while at Biven's Arm it decreased.

Comparisons between male and female feedings reveal little

difference. Sea Horse males and females fed young at the rate of 17.4 and 17.6/15 min respectively and Biven's Arm males and females at a rate of 15.9 and 14.2/15 min respectively. Table 22 gives data on the growth rates for the young from six nests on Biven's Arm late in the 1973 season. The rate of growth was highest for the single nestling on nest six (37.8 g/day). On the nests with two offspring, the firstborn grew faster (26.8 versus 15.0 g/day for the second-born). However, growth is more rapid after the first few days and the data for the second-born are primarily from these early days. On the only three egg nest measured, there was no observable depression of the growth rate of the first and second nestlings (30.9 and 31.4 g/day).




76






Table 22. Growth rates to 5 days for young from 6 nests
on Biven's Arm late in the 1973 season. Note
slower growth of 2nd young and lack of depression
in rate for nest with three young.

Date
Position
Nest in Clutch 6 July 8 July 11 July A Wt. (g) A Wt./Day

6 1 39.0 67.0 228.0 189.0 37.8 g

7 1 61.5 98.0 215.0 153.5 30.7
2 Egg 55.5 99.0 43.5 14.5
8 1 55.0 68.0 172.0 117.0 23.4
2 Egg 36.5 62.0 25.5 8.5
18 1 72.0 75.0 180.0 108.0 21.6 2 44.5 57.0 107.0 62.5 12.5

20 1 49.5 83.0 207.0 157.5 31.5 2 Egg 50.0 123.0 73.0 24.3
33 1 97.5 150.0 252.0 154.5 30.9 2 63.0 109.0 220.0 157.0 31.4 3 Egg 34.0 89.0 55.0 11.0

Total 1296 24.0

1st young in 2 egg clutch 26.8 (n = 4). 2nd young in 2 egg clutch 15.0 (n = 4).




77



As the days pass, the mobility of the young increases and they venture farther from the nest site. At about age four weeks they have attained minimum flight ability and cross short distances between branches. At this age they return quickly to the nest site while vocalizing, when the parent returns. If the young fail to return, the adult looks around and, within a minute, begins to utter single soft honks. By five weeks of age the young never return to the nest site but, instead, remain roosted in the treetops. The adults land in the area and generally are approached immediately by the young birds. Occasionally the young fly to the wrong adult and are attacked with bill thrusts. The response of the young is the same as that of a submissive adult--a quick turn away from the aggressor with compressed plumage. This response terminates the adult's attack.

When the right adult and young are matched in the treetops, a period of intense activity ensues. While the young seven days old initiate feeding, by five weeks their size, strength and eagerness are almost overpowering. The adult turns away as the young bird approaches and often extends its wings for balance. The young beat their wings and vocalize while hitting the parents bill with their own. At an age of two weeks the nestlings place one wing over the back of the adult and by five weeks this exerts a considerable restraining influence. The young are fed by the same regurgitation process for the same three to 10 second interval but only to a maximum of three times at any one perch. Then the adult flies, usually several feet away, and the young follow. At the new roost the process may be continued.




78



As the young approach independence (6-7 weeks), the adults

feed them only once/perch and they fly off, with the young pursuing. The resulting pursuit flights usually involve one young and a parent, but on Biven's Arm as many as three young have been observed following a single adult. The flight may last up to several minutes, with the adult circling and often landing in close proximity to the point of departure. The young, even in flight, continue the high-pitched vocalizations and generally, the first young to the adult is fed.

Once independent of the nest site the young on Sea Horse do not merely wait in the treetops for the adults, but form flocks that walk about on the island. Mid-morning flocks walk down the hill from the dry, sandy clearing to the basin and feed along the exposed mud banks at low tide, with individuals showing constant motion as they repeatedly probe for invertebrates. Individuals in these feeding flocks exhibit aggressive and submissive behavior such as Forward Threat postures, bill thrusts, and turning away, all similar to the adult behaviors. By placing food in pans at the base of the hill, it was possible to observe these interactions at an intensified level due to the high densities of young birds that developed.

Over several days the young ibises at Sea Horse established a linear dominance hierarchy which determined access to food at the feeding station I provided. When a new member arrived it was challenged by those present. The Forward Threat was shown, followed by bill gaping, bill thrusting (with a simultaneous harsh vocalization) and, in high intensity interactions, grasping of the opponent's head and neck. The new bird would either return the aggression or turn away with the head




79



down and feed. If the new bird was aggressive and the established bird turned away, the former became dominant. If the established bird re-thrusted, then it became dominant and had first access to food. No observed aggression went beyond these three exchanges and, once established, no submitting bird ever showed subsequent aggression toward the dominant. The latter merely had to raise its head or administer a single bill thrust to elicit turning away. When the food was plentiful, the more aggressive birds allowed the others to feed in close proximity. As the food became scarce, however, all submitting birds were driven away. Relationships of known young were stable over several days and appeared positively correlated with size.

Crustaceans make up the bulk of the young ibises' diet on Sea

Horse. Fiddler Crabs (Uca spp.) abound on the island and are a popular food source. The ibises probe into the burrows, extract the crab, bill it continously while adjusting its position, and swallow it with the long axis of its body parallel to the bird's throat. Large male fiddler crabs may grab the ibises' bill. When this occurs the bird gives several billshakes until the crab relinquishes his hold. The crab is then grasped by the arm at the proximal end and shaken until the arm is autotomized. The arm is then discarded and the crab consumed. An alternate response to pinching by a crab is complete disinterest subsequent to freeing the bill. Female fiddler crabs (without the large claw) are selected before males by the young birds.

The young ibises selected fish before fiddler crabs when presented with a choice at the feeding station, but were very inefficient at capture. On several occasions fish intended for the young birds were




80



thrown too close to the water's edge and escaped. In such a situation the young were totally inept at pursuing the fish. Some young birds even carried sand covered fish to the water, and submerged them. In these cases the fish quickly escaped. The analysis of Nesbitt et al. (1974) reveals that fish constitute only 1.0% of the ibises' diet.

Feeding activities are most pronounced at low tide during the morning and evening hours. Figure 10 graphs the relationship between the number of ibises feeding in the basin and the time of day, with the tide extremes indicated. While low morning and evening tides result in intense feeding, low tides in the afternoon fail to stimulate much activity. Observations were made through a complete tidal cycle but, as the graph shows, by 23 July most of the young had left the island and few were seen even at low tide in the morning.

The young drink at any standing fresh water source, but were never seen drinking salt water. They dip the head and neck, keeping the bill horizontal until it enters the water. They then raise the head, elevate the bill about 10 degrees above the horizontal, and open and close the bill four to 10 times while swallowing. This action may be repeated up to 20 times in a drinking episode.

Seven-week-old young showed a curious behavior on the white sand of the clearing at Sea Horse. In a flock of 20 young birds, 10 turned their backs to the sun, spread their wings, and laid down on the hot sand while simultaneously gular fluttering. After 13 minutes in this position, the birds rose and walked into the shade, continuing to gular flutter. This spreadwing posture was seen only once and never in the shade.






35 o e- 9 July / o---o 10 July / i..... A 16 July / **
30 1 A- .-A 23 July

/L LT Low Tide (for date indicated) 25 I/ HT High Tide (for date indicated)



S20 I \



15 I I \

---0 LT
1- 0 LT
0

\ A/ ., \ 'A
s. .


0600 0800 1000 1200 1400 1600 1800 2000 Hours
Figure 10. Young feeding in basin vs. time of day

Figure 10. Young feeding in basin vs. time of day (and tide level).




82



Table 23 gives data on rates of survival for both Sea Horse and Biven's Arm. Overall survival is higher on Sea Horse (76.0% versus 69.0% for Biven's Arm) but the rate for Biven's Arm is strongly dependent on the lateness of the season. Here 84.0% of the young from the early nests survived to 10 days while only 41.0% survived from the late pairs. On Sea Horse all of the data are for early nesters. Rates of survival for 20 nests on Sea Horse during the 1974 season were correlated with the height of the nest. Eighty-five per cent survived from the nests lower than seven feet while only 67.0% survived from the nests over 20 feet.

On Sea Horse, the apparent termination of care of the young was

observed twice. In both cases the adult circled with the young pursuing and then flew for the mainland instead of landing. Usually the young break off pursuit while still within a few hundred meters of the island, but these two young birds were observed following the adult until both were out of sight. No young were ever seen returning to the island during this period, suggesting that, once to the mainland, the young do not return until adulthood. Fewer than 30 first year birds (with easily distinguishable plumage) have been seen on Sea Horse in 4 years, so the departure in pursuit of the adult precipitates an extended absence.


Comparisons Within the Order

Table 24 shows the major displays of the Openbilled Storks and Wood Storks, constituting the tribe Mycteriini, the "typical" storks in the tribe Ciconiini, the Marabou Stork in the tribe Leptoptilini









Table 23. Survival rates of young to 10 days. Sea Horse vs. Biven's Arm and Sea Horse
high vs. low nest and Biven's Arm early vs. late in season.


Sea Horse Biven's Arm No. No. Young No. Young No. No. Young No.Young Date Nests Initial 10 Days % Nests Initial 10 Days % 1971 5 10 7

1972 10 20 16 -- -- Early 1973 5 11 8 6 18 16 Late 1973 -- -- -- 8 17 7 1974 10* 21 14 5 13 10 10** 21 18 -- -- -Totals Overall 40 83 63 76% 19 48 33 69% .*height >20 ft. 10 21 14 67% Early 11 31 26 84%
**height < 7 ft. 10 21 18 86% Late 8 17 7 41%





Co




84




(Kahl, 1972e), in comparison with the White Ibis. Display descriptions are taken from Kahl (1966, 1972b, 1972c, 1972d). Table 25 gives similar data for the Green Heron, Snowy Egret, Cattle Egret, and the Great Blue and Great White Herons. Descriptions are taken from Meyerriecks (1960) who considers the Great Blue and Great White Herons as color phases of the species Ardea herodias, Blaker (1968), and Lancaster (1970). These species were selected due to the range of sizes they represent. Furthermore, the Snowy and Cattle Egrets demonstrate breeding requirements similar to the ibises'.

A comparison of the two tables shows that the displays of the White Ibis most closely resemble those of the storks. Each major behavior pattern in the ibises' repertoire has an apparent counterpart in at least one of the stork tribes. According to Kahl's analysis, the storks vary widely in the degree of ritualization of each behavior pattern. The term ritualization, as applied in this study, refers to the process of modification (through stereotypy, simplification, exaggeration, repetition, etc.) of a communicative signal (= display) from original behaviors performed during times of conflicting motivation (see the discussion of Pair Formation). The Marabou Stork performs the most elaborate (and modified) displays and the Openbilled and Wood Storks (Mycteriini) the least elaborate. The Openbills also have the least number of displays. Most of the heron displays differ in appearance from those of the White Ibis.

The alert posture looks very similar in all species compared. Only the Marabou Stork deviates, with the addition of wing spreading to the posture. Kahl refers to the alert posture as the Anxiety







Table 24. Comparison of the displays of the White Ibis and four groups of storks
(Ciconiidae). Apparently equivalent displays are listed in the same
horizontal row.

White Ibis Openbilled StorksTl Wood Storks 2 Marabou Stork3 "Typical" Storks4 Forward Threat* Forward Threat (FT) FT FT FT Stab-and-counterstab Clattering Threat (CT)* CT* CT** -Alert Posture Anxiety Stretch (AS)* AS* AS** AS* Up-Down greeting Up-Down greeting (UD) UD UD** UD**
Cop. Bill Shake Cop. Clattering (CC) CC CC CC Display Preen -- Display Preen -Head Roll* Head Rubbing (HR) HR HR HR Snap** Swaying Twig Grasp (STG) STG** STG Headshaking Crouch
-- Snap [unlike Ibises'] (S) S S -Upright Display (U) U U U
-- -- Balancing (B) B ----- Aerial Threat (AT) AT AT
--- Gaping (G) Erect Gape --- Advertising Sway** ..
Flying Around
.-- -- Mock Fighting
-- .-- Threat Up-Down Nest Covering Display

Tl From Kahl (1972d); f2 From Kahl (1972b); 3 From Kahl (1966); +4 From Kahl (1972c).
* Slightly ritualized (= modified); ** Highly ritualized.







Table 25. Comparison of the displays of the White Ibis and four heron species (Ardeidae).
Apparently equivalent displays are listed in the same horizontal row.


White Ibis Green Heron Snowy Egret Cattle Egret Great Blue Heron Forward Threat Forward Threat (FT) FT FT FT Stab-Counterstab -- -- Stab-Counterstab -Alert Posture Alert Posture (AP) AP AP AP Up-Down Greeting -- -- -Cop. Bill Shake -- -- -Display Preen -- -- Wing Touch ? Head Roll -- -- Head Rubbing -Snap Snap (S) S -- S
-- Crest Raising (CR) CR CR CR -- Stretch (ST) ST ST ST
-- Upright (UPR) UPR -- UPR Flap Flight (FlF) -- FIF
-- -- Aggressive Upr. (AU) -- AU -- Full Forward (FF) -- -- FF -- Advertising Calls (AC) AC AC AC -- Bittern Stance (BS) BS -- --- Bill Snapping -- --






Table 25. Continued


White Ibis Green Heron+l Snowy Egret Cattle Egret Great Blue Heron

-- Circle Flight -- -- --- -- Aerial Stretch -- --- -- Tumble Flight -- --- -- Jumping Over -- --- -- -- Back Biting --- -- -- Greeting Ceremony -1 From Meyerriecks. (1960).
T2 From Blaker (1969).




88




Stretch display, emphasizing the social signalling function of this response to disturbance. The neck extension and head cocking serve the individual more directly, however, by increasing its field of vision. I choose to stress this apparent function in the naming of the posture.

All species demonstrate the Forward Threat as well, although in this display the ibis differs from all others by extending the neck. The more intense Full Forward display of the Green Heron does include extension of the neck, however.

Ritualized fighting is performed by the White Ibis, Cattle Egret, and all but the "typical" storks (Ciconiini). Kahl gives the name Forward Clattering Threat to this activity for the storks, whereas I prefer the more descriptive Stab-and-counterstab, used by Blaker (1968) in his description of ritualized fighting for Cattle Egrets. This display in the Marabou Stork is least similar to the ibises' while the Openbills and Wood Storks show the greatest similarity. Pictures of the Forward Clattering Threat of the Wood Stork (Kahl, 1972b, Plate 3) look very much like the ibises' posture (Plate 3a). Stab- and counterstab is not described by Meyerriecks for any of the herons he studied (1960).

The Up-Down greeting display is remarkably similar between the storks and the White Ibis. All storks perform it, and the description and pictures of it for the Openbills fit the ibises' pattern precisely, including the honking vocalization of Anastomus oscitans, the neck extension of the male over the female, and the frequent twig pulling at the end of the display. The Wood Storks add a side-to-side motion




89




to the neck arching,the Marabou Stork throws its head further back and bill clatters, and the "typical" storks, while showing considerable variation, are all more elaborate than the ibis and the Openbills. The Up-Down is performed as a greeting in all species. No display resembling this has been described for the herons.

All of the storks and the White Ibis perform copulatory bill shaking. The stork male always performs the Copulation Clattering while the female does the Bill Shaking during copulation of the White Ibis. No copulatory bill shaking of any kind has been described for the herons.

The Wood Storks and the White Ibis perform Display Preening, and from Kahl's description (1972b) both do it the same, by running the bill along the outer edge of the wing. The Wing Touch of the Cattle Egret, as described by Blaker (1969) sounds very similar to this pattern, but no comparable display is described for the other herons.

The two major pair formation displays of the White Ibis, Head Rolling and the Snap display, have no precise equivalents among the stork displays. The storks do show the unritualized head rubbing that constitutes Head Rolling, but there is no mention of an increase in its performance during pair formation. Kahl (1966) describes a Snap display but it is unlike the Snap of the ibis. It involves merely a bill gape from an erect posture. However, the Swaying Twig Grasping of the Openbills, Wood Storks, and Marabou Stork (for which it is most highly stereotyped) resembles the ibises' Snap. In this display, unmated or newly mated males bend forward and lightly grasp twigs. Frequently the male turns (= sways) his body through as much as 80 degrees between performances, much as the ibis male does during the Snap display.




90




Unmated male Openbilled Storks also perform an Advertising Sway in which they bend over with the bill low and pointed back 25 degrees beyond the vertical, and shift their weight from one foot to the other while swaying the bill slowly from side to side (Kahl, 1972c). It is highly ritaulized, according to Kahl, and shows an "obvious relationship" to Swaying Twig Grasping. He reports that it is performed only by unmated males who are apparently trying to attract females. The Snap of the White Ibis has the same function.

Among the herons Head Rubbing has been reported for the Cattle Egret only (Blaker, 1969). All of the herons show a Stretch display in which the head is brought into contact with the back feathers, but it is apparently derived from an intention movement for flight rather than from preening (Daanje, 1950). Also, the heron Stretch does not function in pair formation but, rather, functions in nest relief, synchronizing nest construction, and as a pre-copulatory gesture by the female (Meyerriecks, 1960).

The Snap display of the Green Heron and the Snowy Egret is

essentially identical to that of the White Ibis. It is performed only by the male during pair formation, and there is considerable variation in its performance (including Head Bobbing). Snowies sometimes perform the Snap off the nest site but the Green Heron never does. Meyerriecks (1960) believes the Snap originated in twig pulling movements for the herons, but Baerends and Van Der Cingel (1962) disagree (see discussion of diaplays).

Both the storks and herons demonstrate displays not seen in the ibis. Among the storks, the Openbills show the fewest number of




Full Text
38
remained in the flock less than five minutes. These flocks formed
during the pair formation period are stationary, unlike the mobile
feeding flocks seen throughout the season, and they are never seen
after the days of pair formation have passed. Both sexes are present.
Copulation
The copulation that marks pair formation, as well as subsequent
copulations, take place at the nest site. The pre-copulatory activities
of both sexes are shown in Table 8.
The male and female stand at the nest site in close proximity,
with the male above due to the female's crouched posture (Plate 6b).
It is from this position that the male reaches over the female's neck,
extends his bill vertically downward, and pulls briefly at a twig with
lateral head movements (Plate 5b). The female responds by lowering
her body and may also join the male in twig pulling. Typically, male
mounts the female from this posture (Table 8). The female shows no
apparent solicitation behavior and she is often motionless prior to the
mount (Table 8).
The male mounts slowly from the side of the female, one leg at a
time (Plate 7a), and usually adjusts his position (= treads) for a few
seconds before beginning to lower himself onto the female's back.
Erection of the scapular feathers by the male often occurs at this
time, especially in the early copulations of the pair (Plate 7b). When
mounted, the female retracts her head and neck and positions her bill
vertically downward. As the male lowers his body, the female begins
to cock her wings over her back, thereby cradling the male, and also


117
the nest by adults are attacked. This is not the case for smaller
young. It rarely occurs and perhaps there has been no selection
favoring recognition at a younger age. At 10 days the young must
also cope with temperature extremes and predators. Their response
to human predators changes from crouching in the nest to attempted
escape at about this age, and it does not seem adaptive on Sea Horse.
They move to the branches' end and leap while the predator is still
several feet away. This departure is fatal unless a very dense under
story or low nest site permits re-entry. Perhaps in more typical
ibis nesting habitat such as the dense stands of mangrove in South
Florida, premature departure from the limb by the young is not so
extreme a behavior since return to the nest from below is easier.
After the ten day change in adult attentiveness, the development
of the young is straightforward. As mobility increases, the adults
begin landing farther away and moving off after feeding the young
briefly. This encourages the young to follow, as strength and balance
improve. The pursuit flight is the culmination of this training by
the adult. The young bird must pursue the adult after each feed in
order to be fed again, learning through short flights the skills
necessary for eventual migration. The added energy expenditure for
what appears to be reduced food is compensated for somewhat by feed
ing of the young bird itself as a member of the all-young flocks that
probe for crabs on the mud flats on Sea Horse. As the adult contri
bution declines this source of food increases.
In these feeding flocks the young show aggression when a localized
food source is available. Free ranging flocks show bill thrusting,


82
Table 23 gives data on rates of survival for both Sea Horse and
Biven's Arm. Overall survival is higher on Sea Horse (76.0% versus
69.0% for Biven's Arm) but the rate for Biven's Arm is strongly
dependent on the lateness of the season. Here 84.0% of the young from
the early nests survived to 10 days while only 41.0% survived from the
late pairs. On Sea Horse all of the data are for early nesters. Rates
of survival for 20 nests on Sea Horse during the 1974 season were
correlated with the height of the nest. Eighty-five per cent survived
from the nests lower than seven feet while only 67.0% survived from the
nests over 20 feet.
On Sea Horse, the apparent termination of care of the young was
observed twice. In both cases the adult circled with the young pursuing
and then flew for the mainland instead of landing. Usually the young
break off pursuit while still within a few hundred meters of the island,
but these two young birds were observed following the adult until both
were out of sight. No young were ever seen returning to the island
during this period, suggesting that, once to the mainland, the young
do not return until adulthood. Fewer than 30 first year birds (with
easily distinguishable plumage) have been seen on Sea Horse in 4 years,
so the departure in pursuit of the adult precipitates an extended
absence.
Comparisons Within the Order
Table 24 shows the major displays of the Openbilled Storks and
Wood Storks, constituting the tribe Mycteriini, the "typical" storks
in the tribe Ciconiini, the Marabou Stork in the tribe Leptoptilini


Table 5. Rates of performance of male pair formation activities (15 males total);
comparison of
each year
and both
sites.
Year
Location
Snaps*
s
n
Head
Rolls*
s n
Preen
s n
1972
S. H.
10.7
5.7
405
1.6
100
1.4
94
1973
S. H.
4.9
3.1
605
0.81
129
3.3
526
1974
S. H.
5.8
3.2
338
2.2
145
3.0
195
1973
B. A.
7.5
5.3
256
1.5
56
2.8
86
Overal1
6.5
4.4
1604
1.5
1.4 431
3.2
1.7 901
*Na7 min


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98
conflict, while unable to attack an opponent, will perform attack
behavior toward another object in the environment with which no
conflicting motivation is felt. The Grass-Pulling of Herring Gulls
(Larus argentatus) at the territorial boundary is a classic example
(Tinbergen, 1959). (3) Displacement activities. Some animals in a
conflict situation perform behaviors apparently irrelevant to the
situation (i.e.3 normally only observed when the animal is experienc
ing a different motivation from those in conflict). The preening
of the Avocet {Recurrir ostra americana) during aggressive encounters
is given by Tinbergen (1952) as an example.
These actions supply the raw materials from which displays
develop, through ritualization. According to Tinbergen (1952) these
conflict behaviors, having acquired a signal function, are modified
to reduce ambiguity. Characteristically, this process of modification
includes stereotyping of the behavioral components (often with
exaggeration and simplification of the original movements), development
of morphological features to enhance the conspicuousness of the signal,
and neurophysiological "emancipation" so that the modified behavior
is performed in the proper context relevant to its new function.
I believe more emphasis should be placed on the transfer of
information that is taking place before any ritualization occurs. In
order for a behavior pattern to become elaborated into a display, its
performance must provide a benefit from the very outset for both the
signaller and the signal receiver, or else selection will not favor
further development. Whether the behavior performed in a conflict
situation be labelled "intention movement" or "displacement activity"


71
Table 19. Feeding rates of young for Sea Horse and Biven's Arm.
Feedings/15 min interval and No.sec/feeding for young
of two age groups.
Sea Horse
Date
Age of
Young
(Days)
Total
Feedings
No. 15 min.
Intervals
Feedings
interval
No. sec. of
Feeding
No.
Feedings
Sec.
Feeding
1971
1-5
131
7
18.7
663.5
118
5.6
6-10
107
7
15.3
229.5
74
3.1
1972
1-5
98
6
16.3
350.5
92
3.8
6-10
272
11.4
23.9
957.5
201
4.8
1973
1-5
10
1
10.0
41.0
8
5.1
6-10
72
3
24.0
250.5
49
5.1
1974
1-5
17
3
5.7
54.5
10
5.4
6-10
58
4
14.5
235.0
47
5.0
Totals
1-5
256
17
15.0
1109.5
228
4.9
6-10
509
25
20.4
1742.5
370
4.7
Overall
765
42
18.2
2852.0
598
4.8


The displays of the pair-forming White Ibis are quite similar
to those of the Storks, but quite different from those of the herons.
The first copulation marks the formation of the White Ibis pair.
Copulation occurs for five days and terminates with the laying of the
first egg. Both paired males and females copulate promiscuously with
birds from neighboring nests. Only the males gather nest material and
their col lection strategy appears designed to permit observation of
their own females. Males violently oppose promiscuous mating attempts
directed toward their mates.
The ibises nest in hardwood trees on both study sites. The
Sea Horse population nested in distinct clusters of pairs and settled
different areas of the island in a consistent pattern each year.
Clutch sizes averaged 2.1 at Sea Horse, 2.9 at Biven's Arm early
in the breeding season, and 2.2 at Biven's Arm late in the season.
The incubation period is 21 days with parents alternating at the
nest site. The extent of inattentiveness to the eggs is strongly
correlated with temperature.
The young are fed by direct regurgitation and one parent remains
with them at all times until day 10. Individual recognition develops
simultaneously with the mobility of the young. Rates of feeding on
Sea Horse are lower than Biven's Arm, reflecting the longer distance
the Sea Horse adults must travel to obtain food. At five weeks of
age the young are fed in the tree tops by the returning parent and
are forced to pursue the adult over increasingly longer distances.
Between feedings on Sea Horse, flocks of six and seven week-old
young birds feed on the mud flats around the island. They are capable
IX


SUMMARY
White Ibises begin arriving at Sea Horse Key in early March.
Their numbers increase over several weeks, with flocks arriving in the
late afternoon and departing for the mainland at daybreak. Activity
at Biven's Arm does not begin until April.
Breeding begins on Sea Horse Key when several hundred birds
remain on the island at dawn. Flocks move over the trees, roosting
briefly in several areas. By noon of the first day males begin to
select display sites and defend them with aggressive behaviors, in
cluding the Forward Threat, the Stab-and-counter Stab Ritual, and
overt fighting.
Once a small display site has been secured, the male begins
performing pair formation activities, including the Snap Display,
Head Bobbing, Head Rolling, Display Preening, preening and feather
ruffling. Females, in response to the behavior of the males, land
nearby and perform Head Rolling, Display Preening, preening and feather
ruffling. They also behave aggressively toward other females.
After displaying for several minutes, the female attempts to
land next to the male, approaching with her head down and plumage
compressed. The male initially responds aggressively, driving off
the female with bill thrusts. Her eventual acceptance by the male
is demonstrated by performance of the Up-Down Greeting Display. The
female may subsequently leave or be driven from the display site. The
first copulation marks the formation of the pair.
121


Plate 5a. Head rolling.
Plate 5b
Neck crossing pre-copulatory activity.


64
incubation (15.8 min per pair) and high on day 20 (48.2) but the days
in between all show times within 2.2 min of each other (31.5 to
33.7).
Table 18 gives rates of performance for several activities during
incubation. These values are actually the percentage of rises (times
off the eggs) during which each behavior is performed and give no
indication of the number of performances per rise. There is a
general decline in activity levels from those of the pair formation
period (Table 4). Incubating birds frequently turn their heads
posteriorly and rest the bill on the back, covered by the back feathers.
This behavior is most common in the early morning and in the rain, but
is seen throughout the day, and rarely, in temporal sequence with
guiar fluttering.
Incubating birds exposed to direct sunlight often resort to
guiar fluttering. The bill is gaped slightly and the throat oscillated
4.0 times per second. This rate is constant for all birds over seven
days old and at all temperatures. The amplitude of the oscillations
appears' to increase with temperature, however.
Rates of nest relief during incubation apparently reflect
distances traveled to obtain food and, in turn, determine the maximum
rate of food delivery to the young when they hatch. On Sea Horse,
exchanges occur once a day. During the intensive observations in 1972,
17 exchanges were recorded. All occurred between 1100 and 2000 with
sexes alternating days on the nest. The individual being relieved at
the nest may begin greeting vocalization when the mate is still 10-15
feet off. After the greeting the relieved bird departs within 30 seconds.


Table 23. Survival rates of young to 10 days. Sea Horse vs. Biven's Arm and Sea Horse
high vs. low nest and Biven's Arm early vs. late in season.
Sea Horse Biven's Arm
Date
No.
Nests
No. Young
Initial
No. Young
10 Days
%
No.
Nests
No. Young
Initial
No.Young
10 Days
%
1971
5
10
7


--
1972
10
20
16
--


Early 1973
5
11
8
6
18
16
Late 1973

--
--
8
17
7
1974
10*
21
14
5
13
10
10**
21
18
--
--

Totals Overall
40
83
63
76%
19
48
33
69%
height >20 ft.
10
21
14
67%
Early
11
31
26
84%
height <7 ft:
10
21
18
86%
Late
8
17
7
41%


900
800
700
600
500
400
300
200
100
1500 1530 1600 1630 1700 1730 1800 1830 1900 1930
Hours
ro
o
3. The number of ibises arriving on Sea Horse through the day during the initial
numerical buildup. 14 March 1974.


LITERATURE CITED
Baerends, G. P., and N. A. Van Der Cingel. 1962. On the phylogenetic
origin of the Snap Display of the Common Heron (Ardea cinevea L.).
Symp. Zool. Soc. Lond. 8: 7-24.
Beebe, W. C. 1914. Notes on the ontogeny of the White Ibis, Guara
alba, Zoolgica 1: 240-248.
Blaker, D. 196 9. Behaviour of the Cattle Egret Ardeola ibis.
Ostrich 40: 75-129.
Blest, A. D. 1961. The concept of ritualization. Pp. 102-124 in
Current Problems in Animal Behavior (W. H. Thorpe and 0. L.
Zangwill, Eds.) Cambridge Univ. Press.
Daanje, A. 1950. On locomotory movements in birds and the intention
movements derived from them. Behaviour 3: 48-99.
ffrench, R. P., and F. Haverschmidt. 1970. The Scarlet Ibis of
Surinam and Trinidad. Living Bird 9: 146-165.
Gilliard, E. T. 1956. Bower ornamentation versus plumage characters
in bowerbirds. Auk 73: 450-451.
Kahl, M. P. 1966. Comparative ethology of the Ciconiidae. Part 1.
The Marabou Stork, Leptoptilos crumeniferus (Lesson). Behaviour
27: 76-106.
Kahl, M. P. 1972a. Comparative ethology of the Ciconiidae. Part 2.
The Adjutant Storks, Leptoptilos dubius (Gmelin) and L. javanicus
(Horsfeld). Ardea 60: 97-111.
Kahl, M. P. 1972b. Comparative ethology of the Ciconiidae. The Wood
Storks (genera Myoteria and Ibis). Ibis 114: 15-29.
Kahl, M. P. 1972c. Comparative ethology of the Ciconiidae. Part 4.
The "typical" storks (genera Ciconia, Sphenorhynohus, Dissoura,
and Euxenura). Zeit. Tierpsychol. 30: 225-252.
Kahl, M. P. 1972d. Comparative ethology of the Ciconiidae. Part 5.
The Openbilled Storks (genus Anastomus). J. fur Ornithologie
113: 121-137.
Kahl, M. P. 1972e. A revision of the family Ciconiidae (Aves). J.
Zool. Soc. Lond. 167: 451-461.
144


MORPHOLOGICAL DESCRIPTION AND MAJOR PREENING MOVEMENTS
The adult is white, with black tips on four outer primaries.
Some of the breeding ibises show a slight buffy wash on the crown.
Outside the breeding season the face, decurved bill, and legs are a
dull pink or orange. At the onset of breeding the soft parts become
deep scarlet, with the exception of the distal 1/3 of the bill, which
appears black on some individuals. The female at this time also
develops a swollen guiar pouch to a much greater degree than the male
(Plate 1). This structure, along with the intense coloration, rapidly
disappears after pair formation. The male has a longer bill than the
female, a feature which aids in sexual identification at all times of
the year (initial sexual identity was determined behaviorally). Palmer
(1962) reports mean bill lengths of 153.3 mm and 124 mm for seven males
and nine females, respectively.
The preening movements of the storks, as illustrated by the
Marabou (Leptoptilos orwneniferous) (Kahl, 1966) and those of the Green
Heron {Butorides virescens), as described by Meyerriecks (1960), closely
resemble that of the White Ibis. The following preening activities are
most common for the White Ibis. The breast and ventral surface of
the neck are preened by extending the neck up and out while pointing
the bill downward, bringing it in contact with the feathers. The bill
is then moved from side to side over the feathers, or opened and closed
rapidly over the feathers of a particular area. Typically, the neck
14


Table 9. Post-Copulatory Activities male and female.
Post-Copulatory Behavior 9 Post-Copulatory Behavior
Year
Locality
Slight Preen
Preen
Inactive
Other
Slight Preen
Preen
Inactive
Other
1971
Sea Horse
2
3
13
7
5
4
9
3
1972
Sea Horse
15
12
10
5
12
3
22
3
1973
Sea Horse
1
8
31
11
5
32
10
13
1973
Biven's Arm
3
7
18
1
5
10
8
4
Totals
21
30
72
24
27
49
49
23
Percent;
14.3
20.4
49.0
16.3
18.2
33.1
33.1
15.6


10
plentiful in Gainesville, they were never observed at the rookery.
The predacious Night Heron that is so damaging to the young ibises
on Sea Horse was not observed during this study on Biven's Arm.
Other potential avian predators, such as owls and hawks, are also
apparently absent from the area of the rookery. Alligators and
snakes may constitute a threat to birds on the ground.


40
raises her tail dorso-laterally. The male extends his wings and
depresses his tail ventrally as he descends, positioning his bill
vertically next to the female's bill (Plate 8a). Once lowered, the
male's depressed tail is pumped laterally and the cloacas are brought
into proximity (Plate 8b). In the last 1 or 2 seconds of the act the
male stops lateral tail pumping and pushes forward. By now his center
of gravity has shifted posteriorly and his bill is behind the female's,
although still in a vertical position. In the last second the female
reaches back with her bill, gapes slightly, takes the male's bill in
hers, and shakes it vigorously and audibly. The posture is shown in
Plate 9a. The male then immediately dismounts and the post-copulatory
activities quantified in Table 9 are performed.
Although most copulations proceed smoothly from the initial
mount, the male occasionally places one leg on the female's back and
subsequently withdraws into a normal roosting posture. Such aborted
mounts are the result of disturbance of neighboring birds, female lack
of cooperation (shown by a head-up posture rather than crouching), male
loss of balance, or, simply, apparent lack of sufficient motivation in
the male. Males that repeatedly fail to complete the mounting process
preen vigorously between attempts.
Copulations occur throughout the day, beginning shortly after
dawn and extending until night fall. The rate of copulation is not
constant for each hour in the day, however, as illustrated in Figure 6.
The mean length of the intercopulatory interval is 73 minutes, but this
interval is extremely variable (range = 11 to 191 minutes). Table 10
summarizes the data on the length of the interval as a function of


10
9
8
7
6
5
4
3
2
1
* 1000-1500 hrs only
** 1030-1630 hrs only
J Rain
3 4 5 6 7 8 9 10 11 12 13
19
20
21
22
23
24
25
14
15
16
17
18
19
20
cn
no
9. Number of minutes off the eggs/pr. hr of incubation vs. the day of incubation.


I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
JP
fofessor of Zoology
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Professor of Entomology
This dissertation was submitted to the Graduate Faculty of the Department
of Zoology in the College of Arts and Sciences and to the Graduate Council,
and was accepted as partial fulfillment of the requirements for the degree
of Doctor of Philosophy.
March, 1975
Dean, Graduate School


119
Comparisons Within the Order
The degree of behavioral similarity between the storks and the
White Ibis suggests that they are more closely related to each other
than either one is to the herons. Even the elaborate displays of the
Marabou Stork apparently have their origin in the simple patterns of
the Openbills and the Wood Storks. The displays of the White Ibis bear
the closest resemblance to those of the latter two groups, particularly
the greeting and ritualized fighting. However, generalizations concern
ing all of the ibises must await further research.
The Snap display of the herons does appear quite similar to the
Snap of the White Ibis, and this is the pattern conspicuously absent
among the storks. However, the Swaying Twig Grasping of the storks
may well represent the ancestral pattern from which the Snap arose.
Twig pulling is associated with the Snap in both the herons and the
White Ibis, and the constant directional changes of the ibis are not
unlike the "sway" seen in the stork display. The Openbilled Storks'
Advertising Sway also has this oscillation as a component, is employed
in the same context as the White Ibises' Snap, and is derived from
Swaying Twig Grasping. Whereas the Snap of the herons resembles the
ibises', it is performed in a different context.
The proliferation of aerial displays and vocalizations of the
herons is not seen in either the storks or the White Ibis. It is
suggested elsewhere that these may have developed as behavioral
isolating mechanisms. The nature of the behaviors indicates that they
may have evolved in a dense habitat in which visibility was reduced,
necessitating the development of aerial maneuvers and vocalizations.


THE REPRODUCTIVE BEHAVIOR AND ECOLOGY OF THE
WHITE IBIS (EUDOCIMUS ALBUS)
By
THOMAS J. RUDEGEAIR, JR.
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1975

ACKNOWLEDGMENTS
I would like to express my gratitude to my advisory committee,
Jack Kaufmann, Jim Lloyd and David Johnston, who guided me during the
collection of data and the writing of this dissertation. Thomas Emmel
and Thomas Patton, who reviewed my work have also been of particular
assistance.
My work on Sea Horse Key was greatly aided by Edward Collingsworth,
who granted me permission to work there, and Frank Maturo, Lee Belcher,
and A. D. Folks who provided transportation and made living on the
island comfortable.
Study of the Biven's Arm rookery was made possible through the
kindness of Jim Wing, who donated the use of his boats.
I must also include thanks to my friends for their moral support,
especially Donna Gillis and all who assisted me with data collecting.
My wife, Frannie, deserves special mention. She helped me in the
field, in the preparation of rough drafts, and in solving all resultant
problems. She was my inspiration.
Support for my research was provided by the Department of Zoology
of the University of Florida, an estuarine studies grant from the
Division of Biological Sciences and a grant from the Frank M. Chapman
Memorial Fund of the American Museum of Natural History.
I

TABLE OF CONTENTS
Page
Acknowledgments ii
List of Tables v
List of Figures vii
Abstract viii
Introduction 1
The Study Areas 3
Sea Horse Key 3
Biven's Arm 8
Methods 11
Morphological Description and Major Preening Movements 14
Results 16
The Season 16
Numerical Increase on Sea Horse Key 16
Aggression 21
Pair Formation 26
Copulation 38
Nest Building 46
Egg Laying 58
Incubation 60
Behavior of Young 67
Comparisons Within the Order 82
Discussion 92
Comparison of the Study Areas.. 92
Habitat Comparison 93
Pre-Pair Formation Behavior 96
Pair Formation-Aggression 96
Analysis of Pair Formation Displays 97
Copulation 105
Mating System 107
i i i

Nest Building Ill
Incubation 114
Hatching and Early Life 115
Comparisons Within the Order 119
Summary 121
Plates 124
Literature Cited 144
Biographical Sketch 147
iv

LIST OF TABLES
Tables Page
1 Dates of first occurrences of nesting events
for both localities 17
2 Dates of key nesting events for 12 specific
nests on Biven's Arm (1973) 18
3 Mean ambient temperatures for the months
preceeding breeding 19
4 Pair formation activities of 15 males and 25 females .... 28
5 Rates of performance of male pair formation
activities (15 males total); comparison of
each year and both sites 31
6 Temporal relationships of main pair formation
activities between male and female 33
7 Initial behavior of displaying male when female
approaches and immediately prior to her departure 36
8 Pre-copulatory activities, both sexes 39
9 Post-copulatory activities male and female 41
10 Intercopul atory intervals 44
11 Division of labor for twig placement following
male return with nest material 52
12 Nest site data
13 Data on nesting trees 55
14 Mean and standard deviation (s) of nest heights
for cluster of synchronized nest and overall
values 56
15 Mean and standard deviation (s) of nest diameters
for clusters of synchronized nests and overall
values 57
16 Clutch size data for Sea Horse and Biven's Arm, and from
inland Florida sites (from the Florida State Museum egg
collection) 59
v

17 Minutes off the eggs (inattentiveness) for the
block of time 1200-1500 hrs 63
18 Rate of performance of activities during incubation
period 65
19 Feeding rates of young for Sea Horse and Biven's Arm .... 71
20 Feeding intervals Sea Horse vs. Biven's Arm and
Biven's Arm early vs. late in season for young of
two age groups 73
21 Composite calculation of seconds of feeding/day at
Sea Horse and Biven's Arm, based on data from
Tables 18 and 19 74
22 Growth rates to 5 days for young from 6 nests on
Biven's Arm late in the 1973 season 76
23 Survival rates of young to 10 days 83
24 Comparison of the displays of the White Ibis and
four groups of storks (Ciconiidae) 85
25 Comparison of the displays of the White Ibis and
four heron species (Ardeidae) 86
VI

LIST OF FIGURES
Figure Page
1 Sea Horse Key and surrounding area 4
2 Sea Horse Key (vegetation) 6
3 Number of ibises arriving through the day at
Sea Horse: 14 March 1974 (pre-pair formation) 20
4 Profile of a White Ibis flock in flight 22
5 Sea Horse Key approach routes and favored roosts 23
6 Copulations per hour 42
7 Sea Horse Key map of nesting areas and the order
of settlement of island areas 48
8 Minutes off the eggs (inattentiveness) during
incubation vs. time of day; temperature vs. time
of day 61
9 Minutes off the eggs during incubation vs. day
of incubation 62
10Young in the basin at Sea Horse vs. time
of day 81
vi i

Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy
THE REPRODUCTIVE BEHAVIOR AND ECOLOGY OF THE
WHITE IBIS (EUDOCIMUS ALBUS)
By
Thomas J. Rudegeair, Jr.
March, 1975
Chairman: John H. Kaufmann
Major Department: Zoology
The behavior and ecology of the White Ibis, Eudoaimus albus, was
studied during the breeding seasons of 1971 through 1974 at two
locations in central Florida, an island in the Gulf of Mexico (Sea
Horse Key) and an inland lake (Biven's Arm). Quantitative data were
collected on many phases of the ibises* reproductive behavior, including;
arrival at the breeding grounds, aggression, pair formation, copulation,
nest building, incubation and care of the young.
The breeding season extends from early March until August, beginning
earlier at the Sea Horse rookery. Following initial numerical increases
at the rookeries, males select display sites and defend them aggressively.
They then advertise with the Snap Display, Head Rolling and Display
Preening. The females land nearby, face the male, and perform Head
Rolling and Display Preening, exposing the swollen guiar pouch to the
7
male. Mate selection is mutual, as the females approach the stationary
males. Partners greet at the nest with the Up-Dowr. display.
vm

The displays of the pair-forming White Ibis are quite similar
to those of the Storks, but quite different from those of the herons.
The first copulation marks the formation of the White Ibis pair.
Copulation occurs for five days and terminates with the laying of the
first egg. Both paired males and females copulate promiscuously with
birds from neighboring nests. Only the males gather nest material and
their col lection strategy appears designed to permit observation of
their own females. Males violently oppose promiscuous mating attempts
directed toward their mates.
The ibises nest in hardwood trees on both study sites. The
Sea Horse population nested in distinct clusters of pairs and settled
different areas of the island in a consistent pattern each year.
Clutch sizes averaged 2.1 at Sea Horse, 2.9 at Biven's Arm early
in the breeding season, and 2.2 at Biven's Arm late in the season.
The incubation period is 21 days with parents alternating at the
nest site. The extent of inattentiveness to the eggs is strongly
correlated with temperature.
The young are fed by direct regurgitation and one parent remains
with them at all times until day 10. Individual recognition develops
simultaneously with the mobility of the young. Rates of feeding on
Sea Horse are lower than Biven's Arm, reflecting the longer distance
the Sea Horse adults must travel to obtain food. At five weeks of
age the young are fed in the tree tops by the returning parent and
are forced to pursue the adult over increasingly longer distances.
Between feedings on Sea Horse, flocks of six and seven week-old
young birds feed on the mud flats around the island. They are capable
IX

of establishing a linear dominance hierarchy that apparently determines
access to limited food sources. Their feeding activities through the
day are correlated with tidal and temperature fluctuations.
x

INTRODUCTION
The behavior of the members of the avian order Ciconiiformes
has been extensively studied in recent years. Andrew Meyerriecks
(1960), for example, has closely examined the breeding behavior of
four species of herons (Ardeidae) and M. P. Kahl (1966, 1972a, 1972b,
1972c, 1972d, 1973) has studied the reproductive displays of the storks
(Ciconiidae). A third family in the order has been largely ignored,
however. The behavior of the ibises (Threskiornithidae; subfamily,
Threskiornithinae), represented worldwide by some 26 species, has
been studied by only a few workers. The published reports contain
only brief qualitative descriptions of breeding activities; e.g.,
ffrench and Haverschmidt (1970) on the Scarlet Ibis (Eudcoimus ruber),
Skead (1951) on the Hadedah Ibis (Hagedashia hagedash), Beebe (1914)
on the White Ibis (Eudocimus albus) in captivity, and Meyerriecks
(in Palmer, 1962) on the White Ibis.
This study reveals the reproductive behavior of the White Ibis
in quantitative detail including arrival at the breeding area, aggression
and pair formation, details of the mating system, copulation, nesting
strategies, incubation, and raising of the young. Also examined are
the effects of such ecological parameters as varying predation pressure,
food availability, and nest site availability.
Two sites close to the University of Florida campus, an isolated
island in the Gulf of Mexico (Sea Horse Key) and an inland lake (Biven's
1

2
Arm) provide contrasting habitats for nesting White Ibises. Con
sequently, they provide an opportunity to learn of the behavior of
a common but little-studied species and to simultaneously compare
that behavior in two distinct ecological settings.
The discussion emphasizes the adaptive significance of the basic
reproductive strategies employed and the environmental causes for the
differences observed in the two populations. The mating system of the
ibis (monogamy with subsequent mutual promiscuity) is discussed at
length and its possible merits reviewed. Also presented is a brief
summary of the ethological theory of the origin and evolution of
displays, and a consideration of the ibises' pair formation displays
in that context.

the: study areas
Sea Horse Key
Sea Horse Key is a 154-acre island 2.5 miles southwest of
Cedar Key on Florida's Gulf Coast, and approximately 5.5 miles from
the Florida mainland. Figure 1 shows the position of Sea Horse and
the three other islands that collectively comprise the Cedar Keys
National Wildlife Refuge: Snake Key, North Key, and Deadman's Key.
Sea Horse Key is a remnant of a Pleistocene sand dune formed at a
time when the water level was greatly reduced (Wharton, 1958).
The waters around the island are diluted due to the fresh water
influx from the Suwanee River and the Wacassassa River, and support
a typical estuarine fauna and flora.
Sea Horse is surrounded by extensive tidal flats upon which
turtle grass (Thalassia testudimm) and manatee grass [Sy ring odium
filiforme) grow in abundance. In the winter and early spring these
grass flats are covered by only very sparse vegetation, and the
associated epifauna is reduced. By late May the grasses are extensive,
and crustaceans and polychaetes abound on and under the surface.
Along the northern shore where a channel has been dredged, the mud
banks and oyster beds exposed at low tide provide potential feeding
areas for the White Ibis.
These sites in the intertidal zone around the island provide
a limited amount of food for the ibises, especially late in the breed-
3

Figure 1. Sea Horse Key and surrounding area. Snake, North and Sea Horse Keys comprise
the Cedar Keys wilderness study area (from Wharton, 1958).

5
ing season, but the bulk of the food for the young must be obtained
from the brackish marshes along the mainland coast. The round trip
is a minimum of eight miles and feeding flocks have been observed
as far inland as Otter Creek, 20 miles east of Cedar Key.
Nesbitt et al. (1974) report stomach contents of 46 White
Ibises nesting near salt water in Florida (30 from Sea Horse).
Crayfish (Pvocambarus sp.) were found in 44.1% (by volume) of the
stomachs, crabs (primarily Uoa spp.) in 23.4%, and insects (eight
orders) in 24.3%. Vertebrates were less prevalent; fish were found
in 1.0%, reptiles (primarily snakes) in 3.0%, and no amphibians.
Sea Horse Key slopes upward from the north and south shores to
a central ridge running in an east-west direction. Wharton (1958)
describes the flora of the island and the micro-habitat differences
of the northern and southern slopes. His work is the source for the
scientific names of the trees mentioned in this study. The ibises
nest on the slopes in the trees of the oak and bay-dominated hard
wood hammock that thrives there (Figure 2). These 60 acres of
potential nest sites have supported as many as 200,000 White Ibises
(in 1972, according to the staff of the Chassahowitzka Wildlife
Refuge) since the island was first used for nesting in 1960. Nests
are constructed in six species of trees at heights ranging from 2.5
to 40 feet. The forest floor is open in most areas and its wealth
of fallen twigs readily accessible to nest-building birds.
There was virtually no interspecific competition for nest sites
or materials observed on Sea Horse. The ibises nest only on the central
ridge whereas the herons and egrets, including the Great Egrets

Figure 2. Sea Horse Key, showing vegetation and sites of rookeries (modified from
Wharton, 1958).

7
(Casmerodius albus), Black-crowned Night Herons (Nycticorax nycticorax),
Yellow-crowned Night Herons (Nyatanassa violcea), Little Blue Herons
[Florida caerulea), Louisiana Herons (Hydranassa tricolor ruficollis),
and Snowy Egrets (Egretta thula) nest exclusively on the peninsula of
land extending north from the western end of the ridge (Gardner's Arm)
and in the black mangroves (Avicennia nitidia) along the island's north
shore.
There is little danger to nesting ibises on the island. The
only mammals present are the black rat (Rattus rattus) and the gray
squirrel (Scuirus carolinensis). Among the reptiles, only the locally
abundant cottonmouth moccasin (Agkistrodon piscivorus) is potentially
dangerous, and only to individuals on the ground. Of the avifauna, the
Osprey (Pandion haliaetus) and the Bald Eagle (Haliaeetus leucocephalus)
are large enough to potentially be of harm to the adults, but the eagle
is only a rare visitor and the Osprey, while locally abundant, inter
acts very little with the ibises.
The eggs and young of the ibises are in greater danger. Several
hundred Fish Crows (Corvus cssifragus) on the island are constantly
present in the rookery and are frequently seen flying with eggs in
their bills. At hatching, the threat from the crows declines but
predation by the Black-crowned Night Heron begins. This species
has been observed challenging adult White Ibises at their nest sites
for access to the young, rather than merely waiting for an exposed
nest as the Fish Crows do. The effects of the rats on eggs and small
young are unknown. If a nestling should fall to the ground it is
subject to predation by the cottonmouth.

8
Biyen's Arm
Biven's Arm is a 200-acre lake in Gainesville with drainage
onto Paynes Prairie to the southeast. Surrounding the lake is a zone
of small red maples [Acer rubrum) and elders (Sambucus canadensis)
approximately 30 feet in width. On the southwest side of the lake,
this zone takes the form of a series of small floating islands, most
of which are separated from the shore by a narrow water or mud barrier
(depending upon rainfall). Numerous fallen trees, however, usually
render these islands accessible to mammalian predators. Immediately
behind this zone of small trees, on the shore itself, are towering
oak trees (Quercus sp.). While often roosting in these trees, the
ibises nest exclusively in the small maples and elders near the water
(Plate 2b).
Paynes Prairie is an extensive 9,000-acre fresh water marsh
that lies approximately 1.5 miles south of Biven's Arm. It provides
feeding grounds for the ibises near the nesting a^ea. Nesbitt et at.
(1974) also report stomach contents for 125 White Ibises nesting near
fresh water (21 from Biven's Arm). Crayfish were found in 45.3% of
the stomachs, insects (six orders) in 36.7%, and no crabs at all were
found. Fish constituted 0.7%, reptiles, 3.3%, and amphibians 1.2%.
Unlike the segregation observed on Sea Horse Key, the herons and
egrets nest in the same areas as the ibises on Biven's Arm. The entire
nesting area for all Ciconiiform birds is less than 10 acres. The red
maples reach a height of about 15 feet and the elders are less than 10
feet. This initial limitation on the number of potential nest sites
is accentuated by the presence of the competing herons, all of which

9
select sites and have similar nesting requirements. An estimated
maximum of nesting White Ibis pairs on Biven's Arm was 200 in 1972.
Nearby Lake Alice on the University of Florida campus provided
nesting sites for the ibises until the degredation of the area in the
early 1960s, at which time the birds discontinued nesting. Simultane
ously, the previously unused Biven's Arm area became the site of an
active rookery. In recent years, however, the lake has attracted land
developers. As a result, the buffer zone between the birds and the
human population has decreased and human use of the lake has increased.
In 1974 an estimated 30 pairs of ibises fledged young from the Biven's
Arm rookery.
Whereas the number of ibises in the area is low, the pairs nest
in close proximity (nearest neighbor 1.8 feet) and, with the addition
of nesting Little Blue Herons, Louisiana Herons, Snowy Egrets, and
Cattle Egrets (Avdeola ibis), there is considerable competition for
space and materials. Despite this density of nesting birds, Biven's
Arm has at least one advantage. The vast feeding grounds on Paynes
Prairie reduce the time and energy that must be spent flying to gather
food for the young.
The only predators observed on the nesting grounds were two
mammalian species. Raccoons (Pvocyon Lotov) and domestic cats (Felis
domestica) were both observed near the rookery and are presumably
responsible for the large scale nest abandonments and destruction that
occur periodically. The stunted nature of the vegetation prevents escape
from such predation. There is apparently very little avian predation
of the ibises' eggs or young on Biven's Arm. Although Fish Crows are

10
plentiful in Gainesville, they were never observed at the rookery.
The predacious Night Heron that is so damaging to the young ibises
on Sea Horse was not observed during this study on Biven's Arm.
Other potential avian predators, such as owls and hawks, are also
apparently absent from the area of the rookery. Alligators and
snakes may constitute a threat to birds on the ground.

METHODS
Because Sea Horse Key is a National Wildlife Refuge, working
within the hammock is discouraged. Throughout the breeding season
the adult ibises are extremely wary. During pair formation nest sites
are readily abandoned, and later in the season eggs and young are left
exposed to Fish Crows and Night Herons for at least several minutes,
if the adults are disturbed. As a result, all of my observations were
taken from at least 50 feet with the aid of 7 X 50 and 7-15 X 50 zoom
binoculars. I observed from the edge of the trees and from the catwalk
around the lighthouse tower situated in the center of the clearing on
the crest of the main ridge. The tower is built into a large house that
has windows which afforded closer observations of many activities,
although their low position made observation of the nest contents
impossible. Tripods were employed on the tower and from the windows,
and various behaviors were recorded with a Bolex 250 Macrozoom (8:1)
super-8 mm movie camera and a Mamiya/Sekor 1000 DTL 35 mm single lens
reflex camera, with either a 400 mm or 900 mm telephoto lens attached.
Notes were taken on both a Norelco Cassette Recorder and by hand, often
with the aid of assistants. Stop watches were used to determine the
duration of behaviors, and a wrist watch to record the time of day.
During incubation, thermometers and a three-lead theromgraph were used
to determine ambient temperatures in the study area.
Clutch sizes were obtained by single trips through the rookery
each year. I moved as quickly as possible to minimize the length of
11

12
time each adult was off the nest. All nest site data were collected
in the winter months.
On Biven's Arm, observations were made from a rowboat anchored
50 feet from the nest sites. The same recording and optical equipment
was employed here. With the absence of avian predators, disturbance
of the nest site was less destructive here than on Sea Horse since the
nestlings were not subject to attack. This permitted daily visits and
determination of intervals between eggs, both at laying and hatching,
and growth rates of the young. Nest site parameters were measured at
the same time.
Durations of rapidly occurring behaviors were determined by
photographing activities at 18 frames per second and subsequently
counting the number of frames spanned by each. Data throughout are
presented as mean values (designated as x) with the sample size (desig
nated as "n") from which the mean was calculated. Ranges or standard
deviations (designated as "s") are included for most activities.
During pair formation, I selected individual males for observation
based on accessibility. These males were watched intensely through
formation of the pair or abandonment. Simultaneous data were collected
on associated females, including all motor patterns and the timing and
description of approaches to the male.
Attention was directed toward the details of copulatory behavior
and related activities during the four-year study. In addition to spot
observations on most of the pairs on Biven's Arm and the clearing on
Sea Horse, several were observed continuously over three or more days

13
of the five-day copulatory period. For each copulation the time,
duration, pre- and post-copulatory events, and associated behaviors
were recorded. From these data a detailed description of the White
Ibises' behavior during the copulation period was possible, including
copulation rates, intercopulatory intervals, and the extent of
promiscuity.
During the 1971 season six nests on Sea Horse were observed on
10 of the 21 days of the incubation period, and all activities of the
adults were recorded. From this record, taken as early as 1/2 hour
before dawn until darkness, a complete description of incubation
behavior could be generated. The data reveal when each bird stood
over the eggs, what he or she did while up, and when each one resumed
incubation. The rate and dynamics of the exchanges of the adults at
the nest site were also recorded.
Unless otherwise stated, the descriptions of the behavior of
the White Ibis are a result of data from both study areas, and general
izations apply to both. Details are presented for behaviors that differ
between the populations.

MORPHOLOGICAL DESCRIPTION AND MAJOR PREENING MOVEMENTS
The adult is white, with black tips on four outer primaries.
Some of the breeding ibises show a slight buffy wash on the crown.
Outside the breeding season the face, decurved bill, and legs are a
dull pink or orange. At the onset of breeding the soft parts become
deep scarlet, with the exception of the distal 1/3 of the bill, which
appears black on some individuals. The female at this time also
develops a swollen guiar pouch to a much greater degree than the male
(Plate 1). This structure, along with the intense coloration, rapidly
disappears after pair formation. The male has a longer bill than the
female, a feature which aids in sexual identification at all times of
the year (initial sexual identity was determined behaviorally). Palmer
(1962) reports mean bill lengths of 153.3 mm and 124 mm for seven males
and nine females, respectively.
The preening movements of the storks, as illustrated by the
Marabou (Leptoptilos orwneniferous) (Kahl, 1966) and those of the Green
Heron {Butorides virescens), as described by Meyerriecks (1960), closely
resemble that of the White Ibis. The following preening activities are
most common for the White Ibis. The breast and ventral surface of
the neck are preened by extending the neck up and out while pointing
the bill downward, bringing it in contact with the feathers. The bill
is then moved from side to side over the feathers, or opened and closed
rapidly over the feathers of a particular area. Typically, the neck
14

15
feathers are extended during this motion. With the wing held loosely
away from the side of the body, the ibis preens along its outer edge
with a smooth stroke directed posteriorly. With the wings similarly
positioned the bill is brought over the shoulder and pointed vertically
downward to preen the under surface of the wing. The back is preened by
merely turning the head posteriorly and erecting the back feathers.
The abdominal region and ventral tail feathers are preened by bending
the head down and reaching between the legs with the bill.
The bill is rubbed against the oil gland at the base of the tail
and subsequently the bill and the side of the head are rubbed along the
back feathers. This action often grades into rolling of the head from
side to side while keeping it in contact with the back. During preening
activity the head is often shaken from side to side with the bill
pointing vertically downward. This head shaking motion is typically
followed by preening of the ventral surface of the body. Feather
ruffling is performed following a preening bout or, less frequently,
from a motionless roosting posture. The wings are held away from the
sides and alternately shaken up and down, with simultaneous erection
of the back and neck feathers. Finally, the head and neck are shaken
rapidly.
The ibis scratches directly over the wing with the longest toe.
The head is lowered and cocked to bring the area to be attended into
position.
Two types of stretching are common. The wing and leg of the same
side are extended downward and posteriorly, or, both wings are cocked
over the back while the head and neck are extended out and downward.

RESULTS
The Season
The breeding season of the White Ibis in central Florida
extends from as early as mid-March until the end of August, by which
time all of the young birds are fully independent of the parents.
Table 1 shows the dates for first occurrence of several key events
for each year of the study at both of the study areas, and Table 2
pinpoints precise dates for 12 nests on Biven's Arm in 1973. Table 3
shows the mean ambient temperatures at the Apalachicola weather station
for January through April in the years the study was conducted, and
the date of the first observed copulation for each year.
Numerical Increase on Sea Horse Key
The early increase in White Ibis numbers in March is apparent
on the island from late afternoon until nightfall. Most birds leave
the island at dawn in the direction of the mainland and its extensive
marshlands. At 1500 hours flocks begin returning to the island and
continue to do so until nightfall. The number of birds that returns
at this time increases steadily for at least two weeks prior to any
actual breeding activity. Figure 3 shows the pattern of numerical
increase for a day during this period prior to pair formation (14 March
1974).
16

17
Table 1. Dates of first occurrences of nesting events
for both localities.
Sea Horse Biven's Arm
1971
1972
1973
1974
1973
1974
First signs of
numerical increase
3 Mar
10 Mar
19 Mar
12 Mar
First copulation
17 Apr
20 Mar
31 Mar
28 Mar
27 Apr

First egg

24 Mar
4 Apr
--
30 Apr
1 Apr*
First young

15 Apr

23 Apr
21 May

First young alone
at nest
_ _
26 Apr
..
4 May
31 May
*abandoned
--no data

Table 2.
Dates of key nesting
Arm (1973).
events for
12 specific
nests on
Biven's
First Day
Last Observed
Egg
Young
Nest
of Pair
Copulation
1st
2nd
3rd
1 St
2nd
3rd
1
26 Apr
30 Apr
1 May
3 May
5 May
22 May
23 May
7
2
26 Apr
30 Apr
1 May
3 May
5 May
22 May
23 May
?
4
26 Apr
?
30 Apr
2 May
4 May
20 May
21 May
22 May
6
11 Jun
14 Jun
15 Jun
18 Jun

6 Jul
7

7
11 Jun
?
15 Jun
17 Jun
--
5 Jul
7 Jul

8
11 Jun
?
15 Jun
17 Jun
19 Jun
5 Jul
8 Jul
?
9
11 Jun
15 Jun
16 Jun
18 Jun
?
N. H
N. H.
N. H.
13
11 Jun
7
7
?
?
7
?
7
18
11 Jun
?
?
15 Jun
7
7
?
7
20
11 Jun
14 Jun
15 Jun
17 Jun
7
6 Jul
?
?
30
11 Jun
7
16 Jun
18 Jun
?
N. H.
N. H.
N. H.
10
11 Jun
15 Jun
?
?
7
?
?
7
--not laid
N. H. not hatched
? date unknown

Table 3. Mean ambient temperatures for the months preceeding breeding. Date of
the first observed copulation and the mean temperature for the 6 days
preceeding it are also given. Climatic data in F are courtesy of the
U. S. Department of Commerce, Natural Oceanic and Atmospheric Admin
istration (Apalachicola Station).
Year
Jan.
Feb. 1-14
Feb. 15-28
Mar. 1-15
Mar. 16-31
Apr. 1-15
6 Days
Before First
Copulation
Date of
First
Copulation
1971
53.8
49.2
59.8
57.1
59.3
63.1
67.3
17 Apr
1972
58.6
51.4
58.4
59.6
64.6
67.9
64.7
20 Mar
1973
55.0
53.4
52.8
66.3
62.9
63.5
64.2
31 Mar
1974
65.6
59.1
55.1
65.8
61.9
68.2
63.0
28 Mar

900
800
700
600
500
400
300
200
100
1500 1530 1600 1630 1700 1730 1800 1830 1900 1930
Hours
ro
o
3. The number of ibises arriving on Sea Horse through the day during the initial
numerical buildup. 14 March 1974.

21
Whereas single individuals fly to and from the island, flocks
of four to 20 birds are most common. During the evening returns early
in the season flocks of 200 individuals are not uncommon. The ibises
often fly in a Vee formation with individuals equally spaced, but this
structure is quite flexible and changes in a few seconds to an undulating
straight line either parallel or perpendicular to the direction of flight.
Figure 4 illustrates the changing profile of a returning flock sketched
from movie film. The ibises glide frequently and often a wave of
gliding will pass down a column. As a line of birds moves it encounters
local air currents and updrafts, creating undulations like a ribbon in
the wind.
All flocks arriving early in the season fly to the western end
of the island and roost there. Bare mangrove branches in close proximity
to other roosting birds are the most popular sites. Figure 5 shows the
island with its principal approach routes and roosting areas employed
during this period. At dawn the birds fly either directly to the main
land from the western end of the island or east across the island and
off its eastern end. The first indication of the onset of breeding
occurs when several hundred of these individuals fail to leave at dawn.
Aggression
The behavior of individuals that return for the commencement of
breeding activities is noticeably altered. Many do not show character
istic headlong flight but, rather, fly with their bills pointed downward
(examining the vegetation?). Loose flocks land periodically, roost
briefly, and depart. At this time there is virtually no site attach-

22
Figure 4. Changing profile of a linear ibis flock, broken into two
sections. Time scale appears on left (n ~ 100). Sketched
from super 8 mm movie film. Picture taken from Sea
Horse of flock returning from the mainland.

Figure 5. Approach routes of returning flocks as indicated by arrows and principal roosting
areas.(modified from Wharton, 1958).
no
CO

24
ment, overt regression is minimal, and mobility is high. Passive
displacement, the departure of one bird when another lands nearby, is
the most noticeable form of interaction.
By noon of the first day some males select sites from which they
will display and on which the nest will be constructed. As attachment
to this single site increases, aggression toward intruders becomes
more pronounced. Initially males are aggressive toward any individual
that approaches within six to 10 feet. Aggressive behavior takes one
of the following forms.
Forward Threat (after Meyerriecks, 1960, for the Green Heron,
Butorides viresaens, and Kahl, 1966, for the Marabou Stork, Leptoptilos
crumeniferus). Active displacement is accomplished by walking or
flying toward an intruder with the body horizontal and the neck
extended in the Forward Threat posture (Plate 2a). In most instances
this approach results in flight, with the intruder turning his back
to the attacker, compressing the body plumage and lowering the head
(Plate 4a), and walking or flying off. This is less likely to occur
if the other individual is also a resident male with some site
affinity.
Stab-and-counterstab (after Blaker, 1969, for the Cattle Egret).
If the intruder does not retreat, the attacker recoils his neck,
raises the bill above the horizontal, and begins thrusting the
head outward, striking with the gaped, pointed bill. These aggressive
males consistently show erection of the scapular feathers. If the
intruder at this point is equally tenacious he faces the attacker,
assumes a similar recoiled posture (Plate 3a) and also begins bill

25
thrusting. Usually such a bout will take the form of a Stab-and-
counterstab ritual in which male A thrusts toward the head of male
B, while the latter is simultaneously retracting his neck (Plate 3b);
then the process is reversed. This usually results in little physical
contact and continues until one of the combatants turns away or be
gins fighting.
Fighting. When individuals are highly motivated, for example,
during the initial encounter between neighboring males or an unmated
male's first attack of an approaching female, the Stab-and-counterstab
is not demonstrated. At these times aggressive individuals strike
independently at the opponent, frequently biting the head and neck.
It is only during this type of bout that injuries are a likely
possibility. Bill thrusts are performed in 0.3 seconds (n = 33;
s = 0.06).
In violent bill-thrusting bouts at the nest site, the resident
male attempts to move into a position above the intruder and direct
his thrusts downward. This is accomplished by climbing upward or by
actually mounting the intruder. This latter behavior occurs only if
the intruder is a female.
Aerial Aggression. Whereas several of the herons exhibit
aggressive, extended pursuit flights during this early period
(Meyerriecks, 1960), the male White Ibis never travels more than
10 to 15 feet to repulse an intruder and, once the intruder takes
flight, the resident male returns to his display site. Aerial combat in
this species is rare, seen only as a result of apparent accidents in the
timing of displacement attempts. On three occasions males 10 to 15 feet

26
apart flew toward each other simultaneously in apparent mutual dis
placement attempts. The result was a mid-air collision in all three
cases with single bill thrusts exchanged, followed by landing and
turning away by one of the combatants.
Female Aggression. Females demonstrate the same postures,
movements, and feather erection as males, but less readily. Lone
females confine their attacks to other females exclusively and
administer bill thrusts to males only when mated and on the nest
site. Even under these conditions intersexual female aggression is
rare in the absence of her mate. Intrasexual female aggression is
most common during pair formation when females, attracted by the same
male, land close to each other.
Pair Formation
Once a male has succeeded in establishing himself on a display
site, he begins the performance of pair formation activities. All
displaying is conducted at this site and, when displaying, he is mobile
only in the pursuit of an intruder. The following are the principal
activities of pair-forming individuals.
Snap Display (after Meyerriecks, 1960, for the Green Heron;
Kahl, 1966, uses this terminology for a different behavior pattern of
the Marabou Stork). The unmated male White Ibis performs one con
spicuous advertising display, the Snap. The male, from a stationary
position, crouches and simultaneously extends the head and neck out and
downward (Plate 4b). At the apex of the display he may close the
slightly gaped mandibles over a twig and shake it briefly (occurred in

27
18.7% of the displays; 94 of 503). The wings are cocked over the back
(occurred in 43.6% of the displays; 289 of 663) or held at the sides
during the neck extension. The male then assumes a normal roosting
posture. The entire display is performed in 1.1 seconds (n = 35;
s = 0.09). Table 4 gives frequencies of performance of the principal
pair formation activities, including the Snap. The male performs as
many as 25 Snaps/min at the height of display intensity, with a mean
of 6.5 (n = 1604; s = 4.4). He rotates his body constantly and
displays in all directions, never showing any prolonged orientation
toward any particular female in his area. The position of the scapular
feathers is variable during the performance of the Snap, from completely
compressed to fully erected.
A displaying male directs the neck extensions of the Snap down
ward at approximately a 45 angle unless there is another pair within
three feet. The male then directs all extensions toward the pair
when facing it. These Snaps are performed with the wings cocked and
the scapular feathers erected, and they are performed more rapidly
(0.67 sec; n = 4; s = 0.05).
Head Bobbing (new terminology). Head Bobbing, which appears
as a Snap minus a full neck extension, is also performed by displaying
males. It consists of a dipping motion of the head while the neck
remains retracted. It was performed at a rate of 3.7/min by the
three males for which it was quantified (n = 214; s = 2.4) as compared
to a snap rate of 5.9/ min for the same males. While Head Bobbing, the
males did not extend their wings or show associated twig pulling.

Table 4.
Pair formation activities of 15 males and 25 females. These are composite
data for all years at both sites. Data collected throughout the day, from
as early as 21 March until as late as 10 June.
Activity
No./min.
Male
Range s
No.
Displays
No./min.
Female
Range s
No.
Displays
Snap*
6.5
0-25
4.4
1604

--


Head Roll
1.5
0-6
1.4
430
3.8
1-13
2.5
404
Display Preen
2.5
0-8
1.5
157
2.2
0-6
1.5
160
Preen
3.2
0-13
1.7
901
3.5
0-12
1.9
404
Feather Ruffle
0.96
0-4
0.7
62
1.1
0-4
0.75
40
Head Bob
3.7
0-8
2.4
214
_ _
_ _
_ _
* % with wing extensions 42.2
% with twig pulling 18.7
(n = 280 displays of 663)
(n = 94 displays of 503)

29
Two of these three males abandoned their display sites within two
hours after I began observing them.
Only unpaired males perform the Snap and Head Bobbing. All
other pair formation activities by both sexes are apparently intact or
slightly modified preening movements, with only the frequencies of
performance altered.
Head Rolling (new terminology). Head Rolling is performed
by both sexes during pair formation and is the dominant activity of
unpaired females searching for a mate. The bird orients its bill
horizontally and perpendicular to the body. The side of the head is
laid against the back feathers. From this position the head is rolled,
raising the bill above the horizontal. The bill may be carried a
full 180, through the vertical, to the other side, or as little as
30. A normal roosting posture can be assumed after one roll, or the
head may be rolled back and forth for several seconds. A single roll
takes 1.1 seconds to perform (n = 21, s = 0.31). Plate 5a shows an
example of bill orientation when it passes through the vertical position.
The male performs this activity in temporal sequence with the Snap at
a rate of 1.5/min (n = 430, s = 1.4). The female, in response to the
Snap displays of the male, will land within 15 feet of him, face him
directly, and perform the Head Roll at a rate of 3.8/min (n = 404;
s = 2.5).
This behavior appears quite similar to the rolling movements
performed during head rubbing, the preening activity described earlier.
There is little rubbing during the Head Roll, however, and there is
no temporal association between rolling and the oil extraction from
uropygiai gland, as there is during head rubbing.

30
Oriented as she is, the Head Roll of the female exposes her
guiar region to the male that she is watching.
Display Preen (after Kahl, 1972a, for Wood Storks, e.g
Mycteria americana; similar to the Wing Touch described by Blaker, 1968,
for the Cattle Egret). During Display Preening, the bird runs its
bill along the outside edge of the wing, with the wing held briefly
away from the side. It appears as normal preening except that the
bill is often out of contact with the wing feathers. The pair-forming
male shows this behavior 2.5 times/min (n = 157; s = 1.5) and the
pair-forming female 2.2 times/min (n = 160; s = 1.5).
Preening and Feather Ruffling. As shown in Table 4, both
male and female perform preening and feather ruffling intermittently
with the above behaviors. Displaying birds are moving constantly and
rates of performance for these movements are high when compared to
rates for roosting birds not forming pairs. These latter individuals
preen briefly, usually for less than one minute, followed by long
periods of inactivity. Incubating birds, for example, execute a mean
number of 2.6 preening episodes/hour. Males that begin displaying in
an area and are not approached by any females within one to two hours
discontinue this intense activity and then abandon the site. The
rates of performance of displays differ from year to year on Sea Horse
and between Sea Horse and Biven's Arm. Table 5 shows some of these
data.
Table 6 gives a sequential analysis of the main activities of
the male and female during active displaying. All activities were
recorded simultaneously to determine possible cause and effect

Table 5. Rates of performance of male pair formation activities (15 males total);
comparison of
each year
and both
sites.
Year
Location
Snaps*
s
n
Head
Rolls*
s n
Preen
s n
1972
S. H.
10.7
5.7
405
1.6
100
1.4
94
1973
S. H.
4.9
3.1
605
0.81
129
3.3
526
1974
S. H.
5.8
3.2
338
2.2
145
3.0
195
1973
B. A.
7.5
5.3
256
1.5
56
2.8
86
Overal1
6.5
4.4
1604
1.5
1.4 431
3.2
1.7 901
*Na7 min

32
relationships between pair formation behaviors. The female Head
Roll was preceded by the male Snap 27.2% of the time, the male Head
Roll 3.8%, preening 36.1% and inactivity 19.6%. The Snap of the
male was preceded by the female Head Roll 25.0% of the time, female
preening 22.6%, and inactivity 41.8%. The male Head Roll was preceded
by the female Head Roll 23.7% of the time, female preening 13.1%,
and inactivity 55.3%.
Female Approach Attempts. Once a female has located a
male and has performed Head Rolling near him, she attempts to land next
to him on his display site. She flies with her neck extended downward
and her body contour feathers compressed, and crouches low upon land
ing. Initial approaches of this type are usually opposed by the male,
for he immediately administers bill thrusts to the head and neck of the
female. She flees, usually to her original perch, and the male immedi
ately begins to Snap again (an action that is discontinued as soon as
the female arrives). On Sea Horse as many as six females have been
observed surrounding a displaying male and approaching in this fashion.
The maximum number observed on Biven's Arm was two. The female returns
to the male after a mean duration of 5.7 minutes (n = 44), and after
several approaches begins to leave more reluctantly. Initially this
hesitancy increases the male's aggression and the female is forced to
flee.
Up-Down Greeting (after Kahl, 1972c, for the Openbilled
Storks, e.g.y Anastomus oscitans). Acceptance of the female by the
male is indicated by the Up-Down greeting display. As the female
approaches with her head down, the male raises his head and neck, gapes

Table 6. Temporal relationships of main
female.
Snap
Behavior
Relationship
No.
%
cfSnap
Following


cf Head
Roll
Following


9 Head
Roll
Following
43
27.2
^Snap
Followed by
--

^Head
Roll
Followed by
--

9Head Roll
Followed by
38
24.0
^Snap
Simultaneous with
--
--
tfHead
Roll
Simultaneous with


9 Head
Roll
Simultaneous with
24
15.3
pair formation activities between male and
Activity of Opposite Sex
Head Roll Preen Inactivity Other
No.
%
No.
/o
No.
%
No.
%
43
25.0
39
22.6
72
41.8
18
10.6
9
23.7
5
13.1
21
55.3
3
7.9
3.8
57
36.1
31
19.6
21
13.3
45
26.6
43
25.4
67
39.6
14
8.4
8
21.1
9
23.7
20
52.7
1
2.5
9
5.7
59
37.3
32
20.2
20
12.6
19
11.5
17
10.1
124
73.1
9
5.3
7
17.5
4
10.0
27
67.5
2
5.0
8
5.1
40
25.4
70
44.6
15
9.6
CO
CO

34
his bill, and instead of thrusting downward, slowly arches his neck
through 90 to a vertically downward position, simultaneously giving
a soft honking vocalization. He may lower his bill next to the
female's, or he may extend the arch over her, resulting in crossed
necks. The female, still holding her head low, may remain motionless
or join in by also arching the neck from the horizontal to the vertical
with the male. Often brief twig pulling with lateral bill movements
occurs as the bills reach the vertical position, especially in later
greetings by the pair. The pitch of the vocalizations given during
this ceremony are variable from the low "honk" of the male to the
high-pitched scream of the female.
Four males demonstrated the transitional behavior involved in the
change from rejection to acceptance of the female attempting to pair.
Due to the female's crouched posture, the blows to her head are
directed downward and the bill thrusts are administered with typically
rapid pumping motions. For these four males, the females left less
readily after several approaches and each had to attack more vigorously.
The first indication of their acceptance of the female was a redirecting
of the bill thrust adjacent to the female's head rather than at it.
At the end of these thrusts each male showed twig shaking with lateral
bill movements. Initially these redirected attacks were interspersed
with actual blows to the female's head. The next step in the acceptance
process was a reduction in the speed of the redirected thrust as the
males began arching their necks over that of the female. Not all males
demonstrated this transition from pure aggression to greeting. In 11
of 15 cases the male simply switched from one to the other in temporal
sequence.

35
Mutual twig pulling with lateral bill shaking similar to that
performed at the end of the Up-Down display is performed in several
situations by the mated pair. It is seen following a nest disturbance
(for example, following a bill thrusting bout with a neighboring pair),
as a pre-copulatory activity, or without any apparent external stimulus
as the pair stands together at the nest site.
Male acceptance of the female when she approaches is not necessarily
an indication of pair formation. Once accepted, the female may be driven
off subsequently (29 of 60 observed cases) or she may depart without
provocation (31 of 60 observed cases). Table 7 gives the behavior of
the males for 80 approaches by the females including initial reaction
and behavior immediately prior to the female's departure. Prediction of
probable pair formation is difficult until the performance of the
first copulation. Of 15 pair formations observed, only two males
showed the Snap display after their initial copulation (i.e., 13 of 15
no longer performed pair formation displays).
The performance of the above behaviors results in a high
level of activity for pair-forming individuals, and this level is
reduced following the first copulation. One typical Biven's Arm pair
averaged 10.5 and 12.8 activities/min for the male and female, re-
specitvely, during the five minutes preceding the first copulation, and
3.7 and 5.7 activities/min immediately after.
Whereas the nest generally is constructed at the site of pair
formation, 20% (3 of 15) of the pairs abandoned this area after pairing.
Also, birds appeared in the study areas already paired, further in
dicating some mobility following formation. The stimuli for this move
ment are unknown.

36
Table 7. Initial behavior of displaying male when female
approaches and immediately prior to her departure.
Initial cT Behavior
n
& Behavior Prior
to ? Departure
n
(-)* Bill thrust
20
(-) Bill thrust
18
(+) Inactivity
2
(+) Greeting
50
(-) Bill thrust
23
(+) Inactivity
20
(-) Other
7
(+) Inactivity
10
(-) Bill thrust
6
(+) Inactivity
2
(+) Twig pulling
2
(-) Totals
20
(-)
18 (90.0%)
(+)
2 (10.0%)
(+) Totals
60
(-)
29 (48.3%)
(+)
31 (51.7%)
+ denotes acceptance
- denotes rejection

Detailed observations were discontinued at nightfall, but
extensive vocalizations and wing flapping were audible throughout the
night and indicate that at least greetings at the nest site were
taking place at night during the pair formation period.
Whereas flocks of feeding ibises are a common sight at low
tide on Sea Horse Key, a unique phenomenon occurs during the first
few days of pair formation. In 1971 on the south shore, and in 1972,
1973, and 1974 in the basin on the island's north side, flocks of 20
to 100 individuals were observed standing in three to five inches of
water, with less than 10% of the birds feeding (and, more commonly, with
no birds feeding) (Plate 6a). These flocks were open with recruits
arriving and residents departing every few seconds. Arriving birds
invariably landed within three feet of another individual, but the
latter showed no reaction. Occasional single bill thrusts were seen
between individuals that came within a foot of each other, but no
extended aggression occurred. The principal activities of the birds
were: (1) head dipping (approximately 6/min), which consisted of a
lowering of the head into the water and then raising up, sending a wave
of water over the back; in 25% of the cases (n = 72) this was accomplished
by an initial extension of the neck out and downward, a behavior pattern
strongly resembling the Snap; (2) head shaking (approximately 1/min)
following the wetting process; (3) feather shaking (0.5/min) performed
with the legs flexed, resulting in splashing water over the wings and
back; (4) preening (2.0/min). An individual would typically arrive
without incident, dip its head into the water one or more times, shake
the feathers for 10 to 60 seconds, preen and depart. Most individuals

38
remained in the flock less than five minutes. These flocks formed
during the pair formation period are stationary, unlike the mobile
feeding flocks seen throughout the season, and they are never seen
after the days of pair formation have passed. Both sexes are present.
Copulation
The copulation that marks pair formation, as well as subsequent
copulations, take place at the nest site. The pre-copulatory activities
of both sexes are shown in Table 8.
The male and female stand at the nest site in close proximity,
with the male above due to the female's crouched posture (Plate 6b).
It is from this position that the male reaches over the female's neck,
extends his bill vertically downward, and pulls briefly at a twig with
lateral head movements (Plate 5b). The female responds by lowering
her body and may also join the male in twig pulling. Typically, male
mounts the female from this posture (Table 8). The female shows no
apparent solicitation behavior and she is often motionless prior to the
mount (Table 8).
The male mounts slowly from the side of the female, one leg at a
time (Plate 7a), and usually adjusts his position (= treads) for a few
seconds before beginning to lower himself onto the female's back.
Erection of the scapular feathers by the male often occurs at this
time, especially in the early copulations of the pair (Plate 7b). When
mounted, the female retracts her head and neck and positions her bill
vertically downward. As the male lowers his body, the female begins
to cock her wings over her back, thereby cradling the male, and also

Table 8. Pre-copulatory activities, both sexes. The larger sample size for the
female is a result of closer observation of her at this time.
o*Pre-Copulatory Behavior 9Pre-Copulatory Behavior
Year
Locality
Twig Pulling
Inactive
Preen
Twig Pulling
Inactive
Preen
1971
Sea Horse
2
0
0
2
1
0
1972
Sea Horse
0
0
1
1
2
1
1973
Sea Horse
5
0
0
5
11
0
1973
Biven's Arm
8
1
0
8
9
0
Total
15
1
1
16
23
1
Per Cent
88.2
5.9
5.9
40.0
57.5
2.5
CO

40
raises her tail dorso-laterally. The male extends his wings and
depresses his tail ventrally as he descends, positioning his bill
vertically next to the female's bill (Plate 8a). Once lowered, the
male's depressed tail is pumped laterally and the cloacas are brought
into proximity (Plate 8b). In the last 1 or 2 seconds of the act the
male stops lateral tail pumping and pushes forward. By now his center
of gravity has shifted posteriorly and his bill is behind the female's,
although still in a vertical position. In the last second the female
reaches back with her bill, gapes slightly, takes the male's bill in
hers, and shakes it vigorously and audibly. The posture is shown in
Plate 9a. The male then immediately dismounts and the post-copulatory
activities quantified in Table 9 are performed.
Although most copulations proceed smoothly from the initial
mount, the male occasionally places one leg on the female's back and
subsequently withdraws into a normal roosting posture. Such aborted
mounts are the result of disturbance of neighboring birds, female lack
of cooperation (shown by a head-up posture rather than crouching), male
loss of balance, or, simply, apparent lack of sufficient motivation in
the male. Males that repeatedly fail to complete the mounting process
preen vigorously between attempts.
Copulations occur throughout the day, beginning shortly after
dawn and extending until night fall. The rate of copulation is not
constant for each hour in the day, however, as illustrated in Figure 6.
The mean length of the intercopulatory interval is 73 minutes, but this
interval is extremely variable (range = 11 to 191 minutes). Table 10
summarizes the data on the length of the interval as a function of

Table 9. Post-Copulatory Activities male and female.
Post-Copulatory Behavior 9 Post-Copulatory Behavior
Year
Locality
Slight Preen
Preen
Inactive
Other
Slight Preen
Preen
Inactive
Other
1971
Sea Horse
2
3
13
7
5
4
9
3
1972
Sea Horse
15
12
10
5
12
3
22
3
1973
Sea Horse
1
8
31
11
5
32
10
13
1973
Biven's Arm
3
7
18
1
5
10
8
4
Totals
21
30
72
24
27
49
49
23
Percent;
14.3
20.4
49.0
16.3
18.2
33.1
33.1
15.6

Copulations/Pair Hours
0.8
0600 0700 0800 0900 0100 1100 1200 1300 1400 1500 1600 1700 1800
Hours
Figure 6. Copulation rate per pair hour for each hour of the day. Data are composite from all years
in both localities. Within parentheses are the total number of pair hours of observations
at each time.
-p*
PO

43
locality, lateness of the season, and day in the copulatory period
(1 and 2 vs. 3, 4, and 5). The most intense period of copulatory
activity occurred for Pair 3 on 6 April 1973 on Sea Horse (fourth
day of copulation). Following two copulations with other males by
the female at 1012 and 1026 hours, the pair copulated at 1033, 1048,
1100, 1145, 1210, 1308, and 1502.
Between copulations, the male of each pair gathers nest material
and the female constructs the nest. During the male's absence from the
nest site, neighboring males approach and attempt copulation with the
unattended female.
In 330 pair-hours of observation of 26 pairs during the copulation
phase, males attempted to mount females other than their mate 62 times.
Of 26 known females 16 were approached by 15 of 26 males under obser
vation and approximately seven unknown males. Of the 62 attempts only
12 were apparently successful (i.eterminated after lateral tail
pumping by the male and bill shaking by the female).
Only four of the 62 approaches met with even slight female
aggression. In each of these four instances, the female gave one slow
bill thrust in the direction of the male. None of these actually
struck and none was successful in discouraging the copulation attempt.
All 50 unsuccessful attempts were thwarted by another male, 46 by the
female's mate and four by another interloping male also trying to mount.
The female assumed a motionless, slightly crouched posture similar to
the normal pre-copulatory position 56 of the times she was approached.
Twice females greeted interlopers with the Up-Down display in the same
manner that they would their own mate. Males only approached females

44
Table 10. Intercopulatory intervals. The 63 values are grouped
as to locality, time of season and stage of the
copulation cycle.
Intercopulatory
(x min)
Interval
Range n
Locality
Sea Horse 75.5
Biven's Arm 59.7
Time of Season
Early 80.0
Late 58.3
Overall 73.2
Stage of Copulation
1-2 days 65.9
3-4-5 days 77.9
11-191 54
22-124 9
11-186 43
21-191 20
63
21-140 32
11-191 31

45
alone on a nest site and no male traveled more than 15 feet to
attempt copulation. All 15 promiscuous males known to me were already
paired, as were all 16 females. While 15 males were observed in the
pair formation period, none was ever seen approaching nearby paired
females. The most promiscuous female copulated with her mate 63% of
the time (7 of 11), followed by a female who did so 85% of the time
(17 of 20).
The female continues to return to the nest site with her neck
extended and head down throughout the copulation period.
The duration of the greeting display is reduced by the second
day of copulation, as the males frequently arrive and depart with nest
material. Vocalizations become more brief, and often are not given
at all. By the fourth day of copulation and thereafter, the greeting
display is reserved for the return of one of the pair following an
extended absence from the nest. By this time also, the sexual difference
in the pitch of the vocalizations given by each sex during the greeting
has disappeared.
On Sea Horse, the female leaves the nest site for several hours
on the third or fourth day of copulation apparently to feed, as some
are observed flying toward the mainland. During the females absence,
the male usually remains at the nest site. Infrequent departures by
the male occur, and at these times any construction already completed
at the nest site is in jeopardy. Biven's Arm males never leave the
nest unguarded at this time. When the female returns to Sea Horse,
she remains at the nest site until the first egg is laid on the fifth
day of copulation, performing her duties as primary nest builder. The

46
females on Biven's Arm leave the nest site on day three as well but,
unlike the Sea Horse females, they may feed two or more times by the
laying of their first egg.
Early in the copulation period vocalizations are audible at
night but wing flapping is much less evident than during pair formation.
Spot checks indicated that most pairs spend the night together at the
nest site, with approximately 15% of the pairs represented by only one
member after dark.
Allopreening was observed 10 times in the four years of data
collection, all 10 occurring during the copulation period. Performance
of preening was divided evenly between males and females (five each).
Allopreening occurred both before and after copulation and during
periods of nest material collection by the male, apparently independent
of copulatory behavior. Participating pairs ranged from newly formed
to four days old. In all cases the dorsal surfaces (the back and neck)
were the target areas.
Very few copulations occur after the first egg appears on the
fifth day of copulation.
Nest Building
Nesting begins on different parts of Sea Horse over several weeks.
Pair formation is rarely performed by a single couple at a given location
but, rather, by clusters of five to 20 pairs all synchronized within
24 hours of each other and clumped together spatially.
The island is not settled randomly. The earliest pairs each
year nest on the western side of the island, (Area 1, Figure 7).

47
Subsequent pairs form east of this point until they reach the clearing
in the center of the island (Area 2). Pairs then nest on the eastern
side of the island just beyond the clearing (Area 3), and not on the
edge of it, as might be expected. The birds then converge on the
clearing from east and west (Area 4). Finally, nest sites are selected
on the extreme eastern end of the hammock, in the isolated stand of
trees in the northeast section of the island, and in the trees border
ing the south beach (Area 5). In nesting seasons with fewer pairs
nesting, such as 1971 and 1974, Area 5 is not used. Trees in Area 5
are exposed to the formidable onshore winds. The trees in the principal
study area (Area 4) are used every year. The ibises do not nest in the
well-developed stands of black mangrove which occur along the northern
shore of the island around the border of Sea Horse Creek or the entire
Gardener's Arm area, the very sites selected by the herons and egrets.
This segregation of the ibis from the herons is not seen on Biven's Arm.
Here, the herons, egrets and the White Ibises all nest in close proximity
and interact.
When the pair has been formed and copulation has begun, the male
alone begins to gather nest material. I never observed a female gathering
nest material off the nest site or returning to the nest site with
material. The first trips of the male when nest building begins are
brief and often he returns without material. He gathers twigs first
in the immediate area of the nest and nearby unattended sites, and then
moves farther outward. On Sea Horse, although the thick vegetation
prevented continuous observation of males, most collections apparently
take place within 25 feet of the nest. These collecting trips are as

N
Scale
Figure 7. Order of settlement of nesting areas, numbered chronologically. Area 1 settled
first. Entire nesting area is hardwood hammock. (Modified from Wharton, 1958.)
-P*
00

49
brief as they are close to the nest, the mean duration of male absence
from the nest when returning with a twig being 2.8 min (n = 127). Even
when unsuccessful at obtaining any material, collecting males return to
the nest every 4.2 min (n = 42).
At the height of nest building in an area any nest left unguarded
is pirated, usually within 15 min if active males are present. Males
visit abandoned sites repeatedly (as often as 17 times in 30 min) and
whole nests can be disassembled in an afternoon. Throughout nest
building activities, which continue well into incubation, the pair
alternates absences from the nest. Males usually do not steal material
from tended nests, although on two occasions on Sea Horse males from
nearby nests have been observed pulling twigs from beneath an incubating
female.
Males collecting nest material usually interact little with each
other. Aggression occurs when two males simultaneously select the same
twig. This was only observed on Sea Horse when males were on the ground
and covering large areas in search of twigs. Interactions were brief.
One male administered a bill thrust to the head of the other and the
latter turned away and walked off. The first male to the twig was the
aggressor in the few cases observed (n = 4). A single rasping vocali
zation accompanied the bill thrust in all four encounters. Males on the
ground at Biven's Arm were almost impossible to observe, but they did
show considerable movement and wing flapping, suggesting that, in the
limited area in which they were collecting material, competition for
twigs on the ground during nest building and aggression of the type
described above may have been more pronounced than on Sea Horse.

50
In the clearing at Sea Horse males began searching on the ground
for material on the third day of building. While known males collected
twigs close to the nest in all observable areas, individuals were seen
flying over the clearing with material in rare cases, indicating that
collecting some distance from the nest does occur.
Males begin gathering materials at dawn and some males work until
nightfall. Lack of audible wing flapping at night indicates that they
discontinue this activity after dark.
The male grasps twigs firmly with the bill and employs a lateral
or a push-pull motion in loosening them. Once freed in this manner the
twig is adjusted in the bill until the male has grasped it firmly in
the center. He then flies with it to the nest. Long or bulky twigs
are occasionally dropped or get caught in the trees. Males typically
show great perseverence in the pursuit of these problem twigs. One
male that dropped a twig while roosting on a limb near its juncture
to the trunk, reached out quickly with his leg and trapped the falling
twig against the side of the tree. He then reached down with the bill,
grasped the twig firmly, and returned with it to the nest.
When the male returns to the nest with material the female greets
him with a brief Up-Down display. The male may simply place the twig
down next to the female or, if it is small and easily managed, he may
extend his head and neck over the female's and place the twig in that
manner. In either case the female immediately seizes the twig and
begins lateral bill shaking while slowly moving her head forward (the
"tremble shove technique" of Meyerriecks, 1960). The male at this time
may either release the twig immediately or perform tremble shove move-

51
ments with the female. The twig pulling at the end of the greeting
display is now functional. The latter activity occurs most often with
larger twigs in the initial stages of construction.
Table 11 shows quantitatively the division of labor for actual
construction of the nest. The data reveal that while the female is the
principal builder the male makes a considerable contribution, assisting
the female in placement of material in 27% of the cases observed (n =
165). Release of the twig by the male is followed either by his
preening or departure for more material. Males that characteristically
help the female very little still demonstrate twig pulling with her
prior to copulation. Following copulation these males revert to merely
dropping twigs on the nest and departing. Males continue supplying
material through at least the first half of the incubation period.
When relieved at the nest site by the female during incubation,the male
collects for a time before departing for the feeding grounds. Males
have been observed returning up to 15 times with material before
leaving to feed. The female always departs immediately for the feeding
grounds when relieved.
Males show considerable variation in the timing of their gathering
efforts. Some begin collecting twigs immediately after pair formation
and, with the females, build a considerable structure by the third day
of copulation. Others collect very little until the third or fourth
day of copulation and then work intensively for 24 to 48 hours, complet
ing a structure sufficient to hold the first egg on day five. This
variation in the timing of nest building occurs on both Sea Horse and
Biven's Arm.

52
Table 11. Division of labor for twig placement following male
return with nest material.
Locality
Year
9 Only*
9 Predominately
and 9
Equally
Sea Horse
1971
3
0
4
1972
32
40
8
1973
16
15
17
Biven's Arm
1973
12
3
15
Total
63
58
44
Percent.
38.2
35.2
26.6
males never placed twigs alone

53
Nests were painted prior to the breeding season in the clearing
on Sea Horse in 1972. Of 25 painted nests, 22 were completely dis
assembled so that only the painted branch upon which they were constructed
the previous year remained. The remaining three were built upon and
used during the 1972 season. Along the south shore 25 nests were also
painted but the entire area was unused.
Over two winters 1000 nests were examined on Sea Horse and a
variety of parameters measured. Similar data were collected for all
available nests on Biven's Arm. Table 12 shows mean values and standard
deviations for nest heights, diameters, and nearest neighbors for the
two areas. Table 13 shows the percentages of nests in the various
tree species for both areas and the percentage of the total flora each
species constitutes. On Sea Horse the development of the vegetation
beneath the nests is extremely variable, ranging from a dense tangle of
vines to complete absence of flora. The branches upon which the nests
are constructed ranged from under 1/4 inch (for the clusters of vines
in which nests were found 8.6% of the time) to over three inches in
diameter (for the oak trees). Since the Biven's Arm birds nest in only
two species of trees, there is less variation here.
When local clusters of nests are considered on Sea Horse, however,
the variations in height, diameter, tree species, and nature of the
vegetation beneath the nest are much lower. Tables 14 and 15 show the
mean values and standard deviations for the nest height and diameter with
in each cluster, and the species of tree in which each cluster occurred.
In all 44 clusters the standard deviation of the height is less than the
overall value, and in 37 of the 44 clusters the standard deviation of the

54
Table 12. Nest site data. Overall values for Sea Horse
Key and Biven's Arm for nest height, diameter,
and nearest neighbor.
Nest Parameter
Sea Horse
Mean s
n
Biven1s
Mean
Arm
s
n
Height
12.0 ft.
5.3
999
5.9 ft.
1.9
83
Diameter
10.0 in.
1.9
1051
10.1 in.
1.2
78
Nearest Neighbor
3.8 ft.
3.7
1052
1.8 ft.
1.4
72

55
Table 13. Data on nesting trees. Number and per cent of nests
in each species and number and per cent of each species
in hammock on Sea Horse.
Trees in x
Nesting Nest
Nests in t Areas % Height
Species* n Total n Total (feet)
Sea Horse:
Tmala littoralis (Bay) 706
Quercus virginiana (Oaks) 128
Quercus lauri folia
Sabina silioioola (Cedar) 44
Sabal palmetto (Palm) 42
Ilex vomitoria (Yaupon) 41
"vines" 91
Biven's Arm:
Sambucus canadensis (elder) 61
Acer rubrum (Red Maple) 10
67.1
154
36.0
11.6
12.2
111
25.9
18.0
4.2
45
10.5
11.26
4.0
89
20.8
14.19
3.9
29
6.8
5.93
8.6
--


85.9
14.1
*species names from Wharton (1958)

56
Table 14. The mean and standard deviation (s) of nest heights
for clusters of synchronized nest and overall values.
Species*
N in
Cluster
X
Height
(Feet)
s
Bay
5
8.7
0.27
10
5.6
1.40
10
6.8
1.43
13
10.9
1.50
11
10.1
1.58
17
6.1
1.66
12
9.5
1.82
6
16.3
1.86
6
18.5
1.97
7
12.3
2.06
15
14.8
2.24
12
9.8
2.45
9
15.0
2.65
12
13.2
2.67
7
13.4
2.70
9
12.4
3.20
8
11.0
3.25
9
11.4
3.50
9
16.4
3.84
Cedar
5
9.4
0.97
6
10.0
1.90
3
18.0
2.00
7
12.7
2.69
Oak
7
15.2
0.75
7
36.9
1.46
4
9.8
1.50
9
15.4
2.30
5
26.0
2.55
6
19.0
3.10
6
21.3
3.38
5
14.0
3.46
Palm
4
10.0
0.00
5
16.0
0.00
3
17.0
0.00
3
18.0
0.00
3
19.3
1.15
4
15.5
1.73
Yaupon
3
9.0
0.00
3
7.3
0.58
8
3.4
0.73
4
5.6
0.75
7
4.4
0.96
6
3.0
1.00
4
7.0
1.15
All trees in study
999
12.0
5.29
*data arranged in order of increasing s for each species

57
Table 15. Mean and standard deviation (s) of nest diameters
for clusters of synchronized nests and overall values.
Species *
N in
Cluster
X
Diameter
(inches)
s
Bay
6
9.3
0.82
12
9.2
0.87
15
11.1
1.03
9
12.1
1.05
11
9.2
1.08
13
9.1
1.11
7
10.6
1.13
10
10.0
1.15
6
9.7
1.21
12
8.6
1.29
5
9.2
1.30
9
10.2
1.30
7
9.4
1.40
12
10.9
1.51
9
9.8
1.56
17
9.4
1.58
8
9.9
1.73
10
9.4
1.84
9
10.4
2.07
Cedar
7
9.1
1.57
5
10.0
1.59
6
9.8
2.23
3
10.7
2.89
Oak
5
9.0
0.71
6
9.3
0.67
5
10.4
1.14
6
10.5
1.17
4
10.2
1.26
9
9.2
1.30
7
10.2
2.57
7
12.6
2.76
Palm
4
13.8
0.50
4
9.2
0.95
5
13.2
1.10
3
10.7
1.15
3
12.0
2.00
3
9.7
2.08
Yaupon
4
7.8
0.50
6
9.7
0.52
3
7.7
0.58
3
9.3
0.58
4
9.0
0.82
8
8.4
1.19
7
9.1
1.68
All trees in study
1051
10.0
1.89
*data arranged in order of increasing s for each species.

58
diameter is less than the overall value, illustrating the comparative
similarities of these parameters for the nest sites in the clusters.
Also, all of the nests of a cluster have a similar understory and
accessibility, and are composed of similar materials. Because all of
the nests are within a 25-foot radius, the pairs probably experience
similar wind velocities and predation pressures as well. No isolated
nests were observed on Sea Horse, and only four such nests were observed
on Biven's Arm.
The nest itself is constructed entirely of twigs up to three feet
in length and one inch in diameter, with the larger twigs forming the
basic framework and the smaller twigs the cup. The final addition to
the nest is a lining of leaves or Spanish moss. The leaves used are
from the immediate vicinity of the nest, further indicating the local
nature of nest material collection.
Egg Laying
The female lays the first egg on the fifth day after the beginning
of copulation. Incubation prior to completion of the clutch occurs
infrequently on both Sea Horse and Biven's Arm. The second egg is laid
two days later and the third egg (on Biven's Arm) laid two days after
the second (see Table 2). Table 16 gives clutch sizes for several years
on both Sea Horse and Biven's Arm. In every year the mean clutch size
on Sea Horse was <2.2 eggs per nest whereas at Biven's Arm it was
always > 2.8 early in the season. The mean clutch size late in the
season at Biven's Arm dropped to < 2.2, however. Table 16 also gives
data for clutch sizes for various populations of White Ibis from the

Table 16. Clutch size data for Sea Horse and Biven's Arm, and from inland Florida sites
(from the Florida State Museum egg collection).
Locality
Season
One
Egg
Size
Two
Egg
of Clutch
Three
Egg
Four
Egg
X
Sea Horse
1971
0
6
0
0
2.00
1972
4
42
14
0
2.17
1973
8
51
13
0
2.07
1974
7
56
7
0
2.00
Overa!1
19
155
34
0
2.07
Biven's Arm
Early 1973
0
2
20
0
2.91
Late 1973
3
24
9
0
2.16
Early 1974
0
3
13
0
2.81
Early overall
0
5
33
0
2.87
Late overall
3
24
9
0
2.16
Inland Florida sites*
1926
0
3
17
5
3.12
1928
0
2
9
0
2.82
1929
0
0
10
3
3.23
Overal1
0
5
36
8
3.08
*from museum

60
egg collection of the Florida State Museum. For all of these inland
populations the mean clutch size was > 2.8.
Between the laying of each egg, the female feeds while the male
tends the nest, and it is at this time that the alternation of adults
at the nest begins. This phenomenon occurs at both Sea Horse and
Biven's Arm, but the intervals between exchanges at the nest are quite
different (see Table 20).
Incubation
Consistent incubation begins with the completion of the clutch.
Figure 8 shows the relationship between the number of minutes off the
nest (inattentiveness) and the time of day. On the same graph is a
plot of the mean ambient temperature per hour interval, using only
the days of relatively uniform temperature. Both lines assume an
approximate bellshaped curve with maxima at 1500 hours. The smooth
shape of the curve showing the number of minutes off the nest per hour
is disrupted somewhat by the depressed value for the hour 1200 to 1300.
As the graph indicates, all six pairs were shaded over more than 80% of
their bodies at this time.
Figure 9 shows the mean number of minutes off the nest per hour
for each day of observations. Days on which rain occurred and days on
which observations were made only during the hours when temperatures
were highest are indicated.
Table 17 gives values for the number of minutes off the nest
per pair for the block of time 1200 to 1500 hours for each sunny day
in an effort to determine the change in attentiveness as the 21-day
incubation period progresses. Time off the nest is low on day three of

minutes off eggs per pair hour
13
12
11
10
9
8
7
6
5
4
3
2
minutes off eggs
o temperature
all adults in <20% sunlight
o

0
0
0
A
(I
0 §
0
-j 1 1 1 I L
0500 0700 0900 1100 1300 1500 1700 1900
Hours
2100
Figure 8. Incubating adults number minutes off nest vs. time of day and C vs. time of day.
Data are from sunny days of May 1971.
34
33
32
31
30
29
28
27
26
25
24
23
22
cr>
Temperature (C)

10
9
8
7
6
5
4
3
2
1
* 1000-1500 hrs only
** 1030-1630 hrs only
J Rain
3 4 5 6 7 8 9 10 11 12 13
19
20
21
22
23
24
25
14
15
16
17
18
19
20
cn
no
9. Number of minutes off the eggs/pr. hr of incubation vs. the day of incubation.

63
Table 17. Minutes off the eggs (inattentiveness) for the block
of time 1200-1500 hrs. Included here are data for the
warm and sunny days only (1971).
Date
Day of
Incubation
Total min. of
Inattentiveness
1200-1500 hrs.
# of
Pairs
Min.
Pair
8 May
3
95
6
15.8
9 May
4
203
6
33.4
11 May
6
189
6
31.5
18 May
13
159
5
31.9
22 May
17
101
3
33.7
25 May
20
193
4
48.2

64
incubation (15.8 min per pair) and high on day 20 (48.2) but the days
in between all show times within 2.2 min of each other (31.5 to
33.7).
Table 18 gives rates of performance for several activities during
incubation. These values are actually the percentage of rises (times
off the eggs) during which each behavior is performed and give no
indication of the number of performances per rise. There is a
general decline in activity levels from those of the pair formation
period (Table 4). Incubating birds frequently turn their heads
posteriorly and rest the bill on the back, covered by the back feathers.
This behavior is most common in the early morning and in the rain, but
is seen throughout the day, and rarely, in temporal sequence with
guiar fluttering.
Incubating birds exposed to direct sunlight often resort to
guiar fluttering. The bill is gaped slightly and the throat oscillated
4.0 times per second. This rate is constant for all birds over seven
days old and at all temperatures. The amplitude of the oscillations
appears' to increase with temperature, however.
Rates of nest relief during incubation apparently reflect
distances traveled to obtain food and, in turn, determine the maximum
rate of food delivery to the young when they hatch. On Sea Horse,
exchanges occur once a day. During the intensive observations in 1972,
17 exchanges were recorded. All occurred between 1100 and 2000 with
sexes alternating days on the nest. The individual being relieved at
the nest may begin greeting vocalization when the mate is still 10-15
feet off. After the greeting the relieved bird departs within 30 seconds.

Table 18. Rate of performance of activities during incubation period. Included are
rates overall, on rainy days, and on days on which data were collected
during hot hours only.
Pair
Hours
(Pr. Hrs.)
Mo. Times
off the
eggs
Na Min. up
Preen
Twig Pull
Feather
Ruffle
Head Shake
Tail Flick
Stretch
Scratch
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Overal 1
365
3.5
6.9
2.6
1.9
0.20
0.12
0.26
0.24
0.56
Rainy Days
90
1.9
1.9
1.3
0.83
0.36
0.20
0.11
0.07
0.27
Sun Days *
70
4.3
13.9
3.3
2.7
0.13
0.13
0.22
0.29
0.71
*days when data were collected only during warmer hours (1100-1600).
CT>
cn

66
While copulations between partners discontinue with the laying
of the first egg, promiscuous mating occurs in rare instances after
this time (observed three times in four years). Of the four cases
of bill thrusting by females toward approaching promiscuous males,
three took place during these late attempts. After the third day
of incubation no promiscuous mating attempts occur. Males still
approach nearby incubating females but, instead of copulating, they
pirate nest material. The female at this time greets interloping
males with the Up-Down display but does not leave the nest, as she
would if the approaching male were her partner.
The earliest case of shading behavior (dropping wings ventrally
while standing over eggs) was recorded on the afternoon of the fourth
day of incubation (at 1444 hours) with an ambient temperature of
34.0C, measured on the tower. The adult was fully exposed to the
sun. Shading was next seen on the 15th day (at 1423) by one adult,
again in direct sun. At 17 days all four adults observed showed
shading in 33C temperatures (first at 1446), even with no individual
fully exposed to sun. The posture is shown in Plate 9b.
Biven's Arm adults spend several minutes at a time as far as
10 feet from the nest when eggs or very small young are present. This
behavior is extremely rare on Sea Horse.
The incubation period is 20-21 days (see dates in Table 2).
Daily visits to the nest were possible only on Biven's Arm, and here
the young hatch two days apart. This asynchronous hatching indicates
that the first egg begins to develop before the clutch is complete.

67
Behavior of Young
The young escape the egg by pecking a hole at one end of the egg
(usually the blunt end). Adults were never observed assisting in the
process, although when the young has emerged the adult removes the
shell from the nest and discards it with a lateral bill shake. This
same bill movement is seen throughout the cycle when debris falls
into the nest itself. The behavior of the adults changes very little
for the first day of the nestling's life; they rise, reach into the
nest as if turning eggs, shake twigs, preen and sit precisely as before
hatching.
In the first few days of life, the young ibises on Sea Horse are
susceptible to predation by Black-crowned Night Herons. On two occasions
the herons were observed flying with young in their mouths, and their
presence in the rookery is common. Adult ibises defend against
intrusion by the Black-crowns with threat displays and actual bill
thrusting if the heron attempts to land at the nest. Fish Crows also
are capable of taking one-day old birds and their presence also alerts
the adults.
One rather unusual predator destroyed my study site in 1971. An
immature Bald Eagle landed among five nests, resulting in immediate
flight by the adults. Of the seven young present (10 days old) two
were killed outright, two fell to the ground and were lost, one was
displaced from the nest five feet, and the others were unharmed.
The newborn ibis is covered with a soft black down, is blind,
and for the first day is barely capable of raising its head. By the
second day, however, the nestlings can raise up and accept food from

68
the parent. Until day seven all feeding is initiated by the adult that
returns with a crop full of food, positions its bill vertically, and
lightly grasps the bill of the young. This stimulates the young to
raise its head upward, sliding the bill up to the mouth of the adult.
At this point the adult gapes widely and the nestling's head literally
disappears into the parent's mouth. There follows a series of head
jerks as the food is regurgitated directly into the nestling's mouth
(Plate 10b). The process of transfer takes from three to 10 seconds
after the nestling's head is in position. Once fed initially the young
begin issuing a begging call--a rapidly oscillating scream of one to two
seconds in duration repeated as often as every two seconds. In the
first days the bill is held horizontally and not oriented in any par
ticular direction. The head bobs up and down as the nestling calls
with the wings extended and fluttered simultaneously. At about seven
days the young has grown large enough so that it can reach the bill of
the adult when begging (Plate 10a). At this time the bill is no longer
randomly oriented, but is aimed at the distal 1/3 of the adult's bill.
The head bobbing now brings the tip of the young's bill into repeated
contact with the adult's, stimulating the adult to move the bill to
the vertically downward position and gape while the bill of the nestling
slides up and into the adult's mouth. Feeding at seven days still
takes between three and 10 seconds, with head jerking more pronounced
than it is for newly hatched young.
The first young hatched is generally larger than his nestmate(s)
and can reach higher during this active begging. The adult attempts to
feed both by moving its bill away from the larger young once it has been

69
fed one or two times. If the size difference is great, however, the
larger young often climbs over the smaller and succeeds in obtaining
several consecutive feedings. In these cases the differences between
young are augmented further. At times when the adult is attempting to
feed the smallest young, both nestlings often reach for the adult's
mouth simultaneously. This results in the abortion of the feeding
attempt via the assumption of an erect posture by the adult; the nestlings
then revert to the begging vocalization.
Returning adults do not all begin feeding the young immediately.
A period of inactivity may precede the onset. If the young are large
enough to reach the horizontal bill of the adult, the bill is often
placed on the back and out of the nestlings' reach. This behavior also
occurs when the adult has finished feeding the young but they continue
to beg.
Up until approximately 10 days of age, the young locomote poorly
and remain on the nest site, although they do climb onto immediately
adjacent limbs. On two occasions five and seven-day-old young were
accidentally displaced from their own nest by the parent and crawled
into a neighboring one. In both cases they were fed along with the
resident nestlings but subsequently returned to their own nests.
Several young of ages 10-20 days were in a neighboring nest when the
adult returned and these were immediately attacked and driven off.
Young ibises at age 10 days move freely from nest to nest in an area
but are fed only by their own parents. Individual recognition of young
by parents apparently develops at the time the nestlings gain mobility.
Up until the age of 10 days parents continue to alternate at the
nest site. The young are fed by the returning parent intermittently for

70
an hour, with the majority of the feedings occurring in the first 15
minutes. Table 19 gives values for feedings/15 min interval and seconds/
feeding for both Sea Horse and Biven's Arm. Crows and Black-crowned
Night Herons feed on very small young and the vigil by the parents
afford the young some protection. At 10 days of age, however, both
parents begin gathering food simultaneously leaving the young alone on
the nest. For the next 10 to 14 days the young stay in close proximity
to the nest but do visit neighboring sites, returning hurriedly to their
own nest when a parent returns with food. Following feeding the parent
leaves and the young continue their activities. It is during this period
that the behavior of the young is most easily observed--they are large
enough to see and yet too small to be excessively mobile.
All of the maintenance activities of the adults are performed by
the nestlings at this time; preening, leg and wing stretching, scratching,
feather ruffling, twig pulling, and even bill thrusting and allopreen-
ing between nestmates. When alone at the nest the young seek shade
during the afternoon hours. Strange adults arriving at the nest site
may or may not elicit a response from the young. Ten-day-old young show
both extremes from intensive begging to a crouched, motionless posture.
If the young do beg from a strange adult they are attacked,whereas, if
they lie still the adult is not aggressive.
Table 20 shows intervals between feedings for Sea Horse and Biven's
Arm, and the resulting differences in seconds of feeding/day at each site
are calculated in Table 21. Although the Sea Horse adults fed the nest
lings more times per 15 min interval (18.2 versus 14.8 for Biven's Arm)
and fed them longer at each feeding (4.8 versus 4.3 seconds for Biven's

71
Table 19. Feeding rates of young for Sea Horse and Biven's Arm.
Feedings/15 min interval and No.sec/feeding for young
of two age groups.
Sea Horse
Date
Age of
Young
(Days)
Total
Feedings
No. 15 min.
Intervals
Feedings
interval
No. sec. of
Feeding
No.
Feedings
Sec.
Feeding
1971
1-5
131
7
18.7
663.5
118
5.6
6-10
107
7
15.3
229.5
74
3.1
1972
1-5
98
6
16.3
350.5
92
3.8
6-10
272
11.4
23.9
957.5
201
4.8
1973
1-5
10
1
10.0
41.0
8
5.1
6-10
72
3
24.0
250.5
49
5.1
1974
1-5
17
3
5.7
54.5
10
5.4
6-10
58
4
14.5
235.0
47
5.0
Totals
1-5
256
17
15.0
1109.5
228
4.9
6-10
509
25
20.4
1742.5
370
4.7
Overall
765
42
18.2
2852.0
598
4.8

72
Table
19. Extended..
Biven's Arm
Total
No.15 min.
Feedinqs No. sec. of
No.
Sec.
Feedings
Intervals
Interval Feeding
Feedings
Feeding
82
7
11.7
225.5
49
4.6
77
6
12.8
125.5
39
3.2
38
3
12.7
90.0
20
4.5
144
7
20.6
503.5
no
4.6
120
10
12.0
315.5
69
4.6
221
13
17.0
629.0
149
4.2
341
23
14.8
944.5
218
4.3

Table 20.
Feeding
intervals Sea Horse
vs. Biven
1s Arm and
Biven'
s Arm early vs.
late in
season
for young of two age groups.
Sea
Horse
Biven's Arm
Age of
Total
No.
Min.
Total
No.
Min.
Date
Young
Min.
Intervals
Interval
Range
Min.
Intervals
Interval
Range
1971
1-5
662
2
331
233-929




6-10
768
2
384
368-400
--

--

1972
1-5
2046
5
409.2
338-489
-


--
6-10
2207
5
441.4
350-510


--

Early 1973
1-5
761
2
385.5
341-420
824
4'
206
173-230
6-10

--

--
516
3
172
136-196
Late 1973
1-5
6-10
--



>1218
4
>304.5
--
Early 1974
1-5
610
3
203.3
168-240
6-10
--


--
853
5
170.6
118-225
Totals Early
1-5
3469
9
385.4
233-489
1434
7
204.9
168-240
6-10
2975
7
425.0
341-510
1369
8
171 .1
136-225
Overa11
6444
16
402.8
233-510
2803
15
186.7
136-240
Totals Late
1-5
_ _
>1218
4
>304.5


Table 21. Composite calculation of seconds of feeding/day at Sea Horse and Biven's Arm,
based on data from Tables 18 and 19.
Mean No. Sec.*
Feedings*
No.15 min. Feedings^
Seconds Feeding
Locality
Feeding
15 minutes
Day
Day
Sea Horse
4.8
18.2
2
=
175
Biven's Arm
4.3
14.8
3.5
=
223
'fc
From Table 19.
^From intervals between feedings; the number of feedings possible through the day
is approximated (also, on Sea Horse, two feedings/day is the observed maximum).

75
Arm), the Biven's Arm adults could provide approximately 27/ more
feeding time per day (224 versus 175 seconds for Sea Horse) by virtue
of the shorter interval between visits (3.1 versus 6.7 hours for Sea
Horse). Table 20 further shows the increase in the interval for
Biven's Arm late in the season (up to 5.1 hours).
These tables, divided into data for young birds 1 to 5 days and 6
to 10 days old, also reveal changes in rates of feeding with age. Both
Biven's Arm and Sea Horse adults fed the older young more often and at
the same time, more quickly. The data for each year, however, reveal
that these changes did not occur in all years.
Changes in the intervals between feeding visits with the age of
the young were opposite at the two sites. At Sea Horse in both 1971 and
1972 the interval increased with age, while at Biven's Arm it decreased.
Comparisons between male and female feedings reveal little
difference. Sea Horse males and females fed young at the rate of 17.4
and 17.6/15 min respectively and Biven's Arm males and females at a
rate of 15.9 and 14.2/15 min respectively. Table 22 gives data on the
growth rates for the young from six nests on Biven's Arm late in the
1973 season. The rate of growth was highest for the single nestling
on nest six (37.8 g/day). On the nests with two offspring, the first
born grew faster (26.8 versus 15.0 g/day for the second-born). However,
growth is more rapid after the first few days and the data for the
second-born are primarily from these early days. On the only three egg
nest measured, there was no observable depression of the growth rate of
the first and second nestlings (30.9 and 31.4 g/day).

76
Table 22. Growth rates to 5 days for young from 6 nests
on Biven's Arm late in the 1973 season. Note
slower growth of 2nd young and lack of depression
in rate for nest with three young.
Position
Nest in Clutch 6 July 8 July
6
1
39.0
67.0
7
1
61.5
98.0
2
Egg
55.5
8
1
55.0
68.0
2
Egg
36.5
18
1
72.0
75.0
2
44.5
57.0
20
1
49.5
83.0
2
Egg
50.0
33
1
97.5
150.0
2
63.0
109.0
3
Egg
34.0
Date
11 July
A Wt (g)
A Wt./Day
228.0
189.0
37.8 g
215.0
153.5
30.7
99.0
43.5
14.5
172.0
117.0
23.4
62.0
25.5
8.5
180.0
108.0
21.6
107.0
62.5
12.5
207.0
157.5
31.5
123.0
73.0
24.3
252.0
154.5
30.9
220.0
157.0
31.4
89.0
55.0
11.0
Total
1296
24.0
1st young in 2 egg clutch 26.8 (n = 4).
2nd young in 2 egg clutch 15.0 (n = 4).

77
As the days pass, the mobility of the young increases and tne.y
venture farther from the nest site. At about age four weeks they
have attained minimum flight ability and cross short distances between
branches. At this age they return quickly to the nest site while
vocalizing, when the parent returns. If the young fail to return,
the adult looks around and, within a minute, begins to utter single
soft honks. By five weeks of age the young never return to the nest
site but, instead, remain roosted in the treetops. The adults land
in the area and generally are approached immediately by the young
birds. Occasionally the young fly to the wrong adult and are attacked
with bill thrusts. The response of the young is the same as that of
a submissive adult--a quick turn away from the aggressor with compressed
plumage. This response terminates the adult's attack.
When the right adult and young are matched in the treetops, a
period of intense activity ensues. While the young seven days old
initiate feeding, by five weeks their size, strength and eagerness are
almost overpowering. The adult turns away as the young bird approaches
and often extends its wings for balance. The young beat their wings
and vocalize while hitting the parents bill with their own. At an
age of two weeks the nestlings place one wing over the back of the adult
and by five weeks this exerts a considerable restraining influence. The
young are fed by the same regurgitation process for the same three to
10 second interval but only to a maximum of three times at any one perch.
Then the adult flies, usually several feet away, and the young follow.
At the new roost the process may be continued.

78
As the young approach independence (6-7 weeks), the adults
feed them only once/perch and they fly off, with the young pursuing.
The resulting pursuit flights usually involve one young and a parent,
but on Biven's Arm as many as three young have been observed following
a single adult. The flight may last up to several minutes, with the
adult circling and often landing in close proximity to the point of
departure. The young, even in flight, continue the high-pitched
vocalizations and generally, the first young to the adult is fed.
Once independent of the nest site the young on Sea Horse do not
merely wait in the treetops for the adults, but form flocks that walk
about on the island. Mid-morning flocks walk down the hill from the
dry, sandy clearing to the basin and feed along the exposed mud banks
at low tide, with individuals showing constant motion as they repeatedly
probe for invertebrates. Individuals in these feeding flocks exhibit
aggressive and submissive behavior such as Forward Threat postures,
bill thrusts, and turning away, all similar to the adult behaviors.
By placing food in pans at the base of the hill, it was possible to
observe these interactions at an intensified level due to the high
densities of young birds that developed.
Over several days the young ibises at Sea Horse established a
linear dominance hierarchy which determined access to food at the
feeding station I provided. When a new member arrived it was challenged
by those present. The Forward Threat was shown, followed by bill gaping,
bill thrusting (with a simultaneous harsh vocalization) and, in high
intensity interactions, grasping of the opponent's head and neck. The
new bird would either return the aggression or turn away with the head

79
down and feed. If the new bird was aggressive and the established
bird turned away, the former became dominant. If the established bird
re-thrusted, then it became dominant and had first access to food. No
observed aggression went beyond these three exchanges and, once
established, no submitting bird ever showed subsequent aggression
toward the dominant. The latter merely had to raise its head or
administer a single bill thrust to elicit turning away. When the food
was plentiful, the more aggressive birds allowed the others to feed
in close proximity. As the food became scarce, however, all submitting
birds were driven away. Relationships of known young were stable
over several days and appeared positively correlated with size.
Crustaceans make up the bulk of the young ibises' diet on Sea
Horse. Fiddler Crabs [Uoa spp.) abound on the island and are a popular
food source. The ibises probe into the burrows, extract the crab,
bill it continously while adjusting its position, and swallow it with
the long axis of its body parallel to the bird's throat. Large male
fiddler crabs may grab the ibises' bill. When this occurs the bird
gives several billshakes until the crab relinquishes his hold. The crab
is then grasped by the arm at the proximal end and shaken until the arm
is autotomized. The arm is then discarded and the crab consumed. An
alternate response to pinching by a crab is complete disinterest sub
sequent to freeing the bill. Female fiddler crabs (without the large
claw) are selected before males by the young birds.
The young ibises selected fish before fiddler crabs when presented
with a choice at the feeding station, but were very inefficient at
capture. On several occasions fish intended for the young birds were

80
thrown too close to the water's edge and escaped. In such a situation
the young were totally inept at pursuing the fish. Some young birds
even carried sand covered fish to the water, and submerged them. In
these cases the fish quickly escaped. The analysis of Nesbitt et at.
(1974) reveals that fish constitute only 1.0% of the ibises' diet.
Feeding activities are most pronounced at low tide during the
morning and evening hours. Figure 10 graphs the relationship between
the number of ibises feeding in the basin and the time of day, with
the tide extremes indicated. While low morning and evening tides
result in intense feeding, low tides in the afternoon fail to stimu
late much activity. Observations were made through a complete tidal
cycle but, as the graph shows, by 23 July most of the young had left
the island and few were seen even at low tide in the morning.
The young drink at any standing fresh water source, but were
never seen drinking salt water. They dip the head and neck, keeping
the bill horizontal until it enters the water. They then raise the
head, elevate the bill about 10 degrees above the horizontal, and open
and close the bill four to 10 times while swallowing. This action may
be repeated up to 20 times in a drinking episode.
Seven-week-old young showed a curious behavior on the white sand
of the clearing at Sea Horse. In a flock of 20 young birds, 10 turned
their backs to the sun, spread their wings, and laid down on the hot
sand while simultaneously guiar fluttering. After 13 minutes in this
position, the birds rose and walked into the shade, continuing to guiar
flutter. Tin's spreadwing posture was seen only once and never in the
shade.

35
30
25
20
15
10
5
I
0600
o o
i A
9 July
10 July
16 July
\
LT
1
0800
1000 1200 1400
Hours
1600
1800
2000
10. Young feeding in basin vs. time of day (and tide level).

82
Table 23 gives data on rates of survival for both Sea Horse and
Biven's Arm. Overall survival is higher on Sea Horse (76.0% versus
69.0% for Biven's Arm) but the rate for Biven's Arm is strongly
dependent on the lateness of the season. Here 84.0% of the young from
the early nests survived to 10 days while only 41.0% survived from the
late pairs. On Sea Horse all of the data are for early nesters. Rates
of survival for 20 nests on Sea Horse during the 1974 season were
correlated with the height of the nest. Eighty-five per cent survived
from the nests lower than seven feet while only 67.0% survived from the
nests over 20 feet.
On Sea Horse, the apparent termination of care of the young was
observed twice. In both cases the adult circled with the young pursuing
and then flew for the mainland instead of landing. Usually the young
break off pursuit while still within a few hundred meters of the island,
but these two young birds were observed following the adult until both
were out of sight. No young were ever seen returning to the island
during this period, suggesting that, once to the mainland, the young
do not return until adulthood. Fewer than 30 first year birds (with
easily distinguishable plumage) have been seen on Sea Horse in 4 years,
so the departure in pursuit of the adult precipitates an extended
absence.
Comparisons Within the Order
Table 24 shows the major displays of the Openbilled Storks and
Wood Storks, constituting the tribe Mycteriini, the "typical" storks
in the tribe Ciconiini, the Marabou Stork in the tribe Leptoptilini

Table 23. Survival rates of young to 10 days. Sea Horse vs. Biven's Arm and Sea Horse
high vs. low nest and Biven's Arm early vs. late in season.
Sea Horse Biven's Arm
Date
No.
Nests
No. Young
Initial
No. Young
10 Days
%
No.
Nests
No. Young
Initial
No.Young
10 Days
%
1971
5
10
7


--
1972
10
20
16
--


Early 1973
5
11
8
6
18
16
Late 1973

--
--
8
17
7
1974
10*
21
14
5
13
10
10**
21
18
--
--

Totals Overall
40
83
63
76%
19
48
33
69%
height >20 ft.
10
21
14
67%
Early
11
31
26
84%
height <7 ft:
10
21
18
86%
Late
8
17
7
41%

84
(Kahl, 1972e), in comparison with the White Ibis. Display descriptions
are taken from Kahl (1966, 1972b, 1972c, 1972d). Table 25 gives
similar data for the Green Heron, Snowy Egret, Cattle Egret, and the
Great Blue and Great White Herons. Descriptions are taken from
Meyerriecks (1960) who considers the Great Blue and Great White
Heron's as color phases of the species Ardea herodias, Blaker (1968),
and Lancaster (1970). These species were selected due to the range
of sizes they represent. Furthermore, the Snowy and Cattle Egrets
demonstrate breeding requirements similar to the ibises'.
A comparison of the two tables shows that the displays of the
White Ibis most closely resemble those of the storks. Each major
behavior pattern in the ibises' repertoire has an apparent counterpart
in at least one of the stork tribes. According to Kahl 's analysis,
the storks vary widely in the degree of ritualization of each behavior
pattern. The term ritualization, as applied in this study, refers to
the process of modification (through stereotypy, simplification, ex
aggeration, repetition, etc.) of a communicative signal (= display)
from original behaviors performed during times of conflicting motivation
(see the discussion of Pair Formation). The Marabou Stork performs the
most elaborate (and modified) displays and the Openbilled and Wood
Storks (Mycteriini) the least elaborate. The Openbills also have the
least number of displays. Most of the heron displays differ in appear
ance from those of the White Ibis.
The alert posture looks very similar in all species compared.
Only the Marabou Stork deviates, with the addition of wing spreading
to the posture. Kahl refers to the alert posture as the Anxiety

Table 24. Comparison of the displays of the White Ibis and four groups of storks
(Ciconiidae). Apparently equivalent displays are listed in the same
horizontal row.
White Ibis
1
Openbilled Storks
2
Wood Storks
*3
Marabou Stork
+4
"Typical" Storks *
Forward Threat*
Forward Threat (FT)
FT
FT
FT
Stab-and-counterstab
Clattering Threat (CT)
* CT*
CT**

Alert Posture *
Anxiety Stretch (AS)*
AS*
AS**
AS*
Up-Down greeting
Up-Down greeting (UD)
UD
UD**
UD**
Cop. Bill Shake
Cop. Clattering (CC)
CC
CC
CC
Display Preen
--
Display Preen


Head Roll*
Head Rubbing (HR)
HR
HR
; HR
Snap**
Swaying Twig Grasp (STG) STG**
STG
Headshaking Crouch
--
Snap [unlike Ibises']
(S) s
S
--

Upright Display (U)
U
U
U


Balancing (B)
B


--
Aerial Threat
(AT) AT
AT


Gaping (G)
Erect Gape


Advertising Sway**
--
--
--


Flying Around
--


--


Mock Fighting
--


--
Threat Up-Down

--

--
Nest Covering Display
1 From Kahl (1972d); +2 From Kahl (1972b); h From Kahl (1966); $4 From Kahl (1972c).
* Slightly ritualized (= modified); ** Highly ritualized.

Table 25. Comparison of the displays of the White Ibis and four heron species (Ardeidae).
Apparently equivalent displays are listed in the same horizontal row.
White Ibis
Forward Threat
Stab-Counterstab
Alert Posture
Up-Down Greeting
Cop. Bill Shake
Display Preen
Head Roll
Snap
il
Green Heron
ti
Snowy Egret
*2
Cattle Egret
+1
Great Blue Heron
Forward Threat (FT)
FT
FT
FT

--
Stab-Counterstab

Alert Posture (AP)
AP
AP
AP
--

Wing
Touch
?

Head
Rubbing

Snap (S)
S
--
S
Crest Raising (CR)
CR
CR
CR
Stretch (ST)
ST
ST
ST
Upright (UPR)
UPR

UPR
Flap Flight (FIF)
Aggressive Upr. (AU)
FI F
AU
Full Forward (FF)


FF
Advertising Calls (AC)
AC
AC
AC
Bittern Stance (BS)
BS
--

Bill Snapping
--
--
--

Table 25. Continued
White Ibis
Green Heron
1
$1
Snowy Egret
Circle Flight
Aerial Stretch
Tumble Flight
Jumping Over
^1 From Meyerriecks (1960).
2 From Blaker (1969).
Cattle Egret
$2
t
Great Blue Heron
1
Back Biting
Greeting Ceremony
00
I

88
Stretch display, emphasizing the social signalling function of this
response to disturbance. The neck extension and head cocking serve
the individual more directly, however, by increasing its field of
vision. I choose to stress this apparent function in the naming of
the posture.
All species demonstrate the Forward Threat as well, although in
this display the ibis differs from all others by extending the neck.
The more intense Full Forward display of the Green Heron does include
extension of the neck, however.
Ritualized fighting is performed by the White Ibis, Cattle Egret,
and all but the "typical" storks (Ciconiini). Kahl gives the name
Forward Clattering Threat to this activity for the storks, whereas I
prefer the more descriptive Stab-and-counterstab, used by Blaker (1968)
in his description of ritualized fighting for Cattle Egrets. This
display in the Marabou Stork is least similar to the ibises' while
the Openbills and Wood Storks show the greatest similarity. Pictures
of the Forward Clattering Threat of the Wood Stork (Kahl, 1972b, Plate
3) look very much like the ibises' posture (Plate 3a). Stab- and counter
stab is not described by Meyerriecks for any of the herons he studied
(1960).
The Up-Down greeting display is remarkably similar between the
storks and the White Ibis. All storks perform it, and the description
and pictures of it for the Openbills fit the ibises' pattern precisely,
including the honking vocalization of Anastomus osoitans, the neck
extension of the male over the female, and the frequent twig pulling
at the end of the display. The Wood Storks add a side-to-side motion

89
to the neck arching,the Marabou Stork throws its head further back and
bill clatters, and the "typical" storks, while showing considerable
variation, are all more elaborate than the ibis and the Openbills.
The Up-Down is performed as a greeting in all species. No display
resembling this has been described for the herons.
All of the storks and the White Ibis perform copulatory bill
shaking. The stork male always performs the Copulation Clattering
while the female does the Bill Shaking during copulation of the White
Ibis. No copulatory bill shaking of any kind has been described for
the herons.
The Wood Storks and the White Ibis perform Display Preening, and
from Kahl's description (1972b) both do it the same, by running the bill
along the outer edge of the wing. The Wing Touch of the Cattle Egret,
as described by Blaker (1969) sounds very similar to this pattern, but
no comparable display is described for the other herons.
The two major pair formation displays of the White Ibis, Head
Rolling and the Snap display, have no precise equivalents among the
stork displays. The storks do show the unritualized head rubbing that
constitutes Head Rolling, but there is no mention of an increase in its
performance during pair formation. Kahl (1966) describes a Snap display
but it is unlike the Snap of the ibis. It involves merely a bill gape
from an erect posture. However, the Swaying Twig Grasping of the Open-
bills, Wood Storks, and Marabou Stork (for which it is most highly
stereotyped) resembles the ibises' Snap. In this display, unmated or
newly mated males bend forward and lightly grasp twigs. Frequently
the male turns (= sways) his body through as much as 80 degrees between
performances, much as the ibis male does during the Snap display.

90
Unmated male Openbilled Storks also perform an Advertising Sway
in which they bend over with the bill low and pointed back 25 degrees
beyond the vertical, and shift their weight from one foot to the other
while swaying the bill slowly from side to side (Kahl, 1972c). It is
highly ritaulized, according to Kahl, and shows an "obvious relation
ship" to Swaying Twig Grasping. He reports that it is performed only
by unmated males who are apparently trying to attract females. The
Snap of the White Ibis has the same function.
Among the herons Head Rubbing has been reported for the Cattle
Egret only (Blaker, 1969). All of the herons show a Stretch display
in which the head is brought into contact with the back feathers, but
it is apparently derived from an intention movement for flight rather
than from preening (Daanje, 1950). Also, the heron Stretch does not
function in pair formation but, rather, functions in nest relief,
synchronizing nest construction, and as a pre-copulatory gesture by
the female (Meyerriecks, 1960).
The Snap display of the Green Heron and the Snowy Egret is
essentially identical to that of the White Ibis. It is performed only
by the male during pair formation, and there is considerable variation
in its performance (including Head Bobbing). Snowies sometimes perform
the Soap off the nest site but the Green Heron never does. Meyerriecks
(1960) believes the Snap originated in twig pulling movements for the
herons, but Baerends and Van Der Cingel (1962) disagree (see discussion
of diaplays).
Both the storks and herons demonstrate displays not seen in the
ibis. Among the storks, the Openbills show the fewest number of

different activities. Among the herons, the Cattle Egret shares the
most displays in common with the ibis, and has the fewest extras.
The Snowy Egret, Green Heron and Great Blue (= Great White) Heron
perform several unique patterns.

DISCUSSION
Comparison of the Study Areas
Sea Horse Key and Biven's Arm provide habitats for the nesting
ibises that differ in many potentially significant details. Those to
be considered here include: 1) vegetation differences such as tree
species, tree height (and resultant number of potential nest sites),
amount of raw materials available for the nests, nature of the under
story, and the amount of shelter provided (from rain, wind, sun and
predators); 2) proximity to food sources; 3) types of predators; 5)
number of interspecific competitors.
Before any discussion of these differences and their apparent
effects, the basic similarity of behavior between the two populations
must be stressed. All of the behavior patterns of pair formation,
copulation, greeting, nest building and care of the young are essentially
identical at the two sites with respect to the components and duration
of each motor pattern. In cases where differences exist between the
two sites, the behaviors involved are quite variable within one popu
lation or even one pair (e.g.3 rates of performance of the Snap display,
as shown in Table 5). It is the rate of performance of the various
behaviors that differs most widely.
The basic similarity in motor patterns suggests genetic continuity
or, at most, only recent separation of the two populations. It seems
likely that there would be considerable mixing of two populations
92

93
separated by only 60 miles in a species that migrates from as far as
Central America or Northern South America. It is possible, of course,
that the young return to the site of their birth to nest two years
later. The final answer to the question of genetic isolation lies in
an extensive tagging program.
Assuming gentic continuity, any differences observed in the two
populations must arise as a function of local conditions acting on
flexible behavior.
Habitat Comparison
The Sea Horse rookery is vast and diverse. Thousands of ibises
congregate and begin selection of sites and mates among trees with
potential sites of highly variable heights, exposure (to sun, wind, rain
and predators), proximity to each other, and understory. On Biven's Arm
in a typical year perhaps a hundred ibises must compete with several
other species for nest sites of much less apparent variability.
There are several consequences of these differences in the
vegetation and the resultant number and quality of the nest sites. Each
member of the Sea Horse population is presented with considerable choice.
The male must decide on a nest site. The timing of his cycle will
determine which areas of the island are available. Once there, the
microhabitat is a matter of individual selection and retention. The
female has tens or even hundreds of displaying males from which to choose
and the male is typically approached by several females. Mate selectivity
is possible and, for the female, the type of site chosen by the male
from the array of possibilities must be considered an important criterion.

94
The comparatively early onset of breeding on Sea Horse may reflect
the importance of making an early choice of nest site on the island,
despite the possible cold weacher and reduced food availability.
The Biven's Arm male is restricted in his choice of a nest site
and both sexes are restricted in choosing a mate. The displaying male
is fortunate if two females approach. Mate procurement is more difficult.
The most obvious characteristic of Sea Horse is its isolation.
Being three miles off shore helps to limit terrestrial predators but
it necessitates lengthy, energy consuming trips to the mainland for
food. The mud and grass flats around the island are used very little
until the end of the breeding season. The late growth of the grasses
and the high salt content of the invertebrates found there may be the
bases for this lack of use. For whatever reason, however, the lengthy
trip to the mainland results in a slowing of the feeding process. The
maximum of two exchanges and feedings at the nest each day is probably
the key reason for the 2.1 clutch size for the Sea Horse population.
The proximity of Paynes Prairie to the Biven's Arm population
makes at least three trips per day possible early in the season. The
2.9 clutch size reflects this increase in food availability. Late
nesters, however, demonstrate reduced rates of feeding and lowered
clutch size (2.2). This may reflect a reduction in the availability
of invertebrates in mid-summer.
The White Ibis, then, demonstrates local variation in clutch
size, apparently as a function of food availability, a phenomenon well
documented by Lack (1968) for other species. The degree of difficulty
in finding food, however measured, is translated into a rate of egg
production.

95
The ibises of Biven's Arm run the risk of complete destruction
of the nest if a raccoon should gain access to the rookery. It seems
unlikely that fine adjustments in nest position or construction would
reduce the threat. Nest vigilance also seems pointless against such
an aggressive predator. On Sea Horse the problem is different. There
is no threat from the ground, but crows and Night Herons are effective
predators on eggs and young from the air. Crows approach only exposed
eggs, however, and the Night Heron, while more aggressive, will retreat
before an aggressive ibis. Subtle nest positioning that would reduce
conspicuousness from the air and an increase in nest vigilance by the
adult ibises would seem beneficial under these conditions. This type
of predation, therefore, further increases the importance of male nest
site selection and the female's consideration of it.
Differences in nest attentiveness at the two sites may also be
attributable to the differing intensities of predation by visually
orienting avian predators. During incubation and the early days of
the care of the young, the Biven's Arm parents spend portions of time
roosting several feet from the nest, leaving its contents in view. Such
a deliberate exposure is extremely rare on Sea Horse. Even when not
incubating or brooding, the adult stands directly over the nest itself.
The highly synchronous nature of the nesting on Sea Horse is
perhaps related to predation as well. Being one of several nests in
an area, each providing the same potential food source for a predator,
may reduce the possibility of any individual nest being selected. While
most of the ibises were synchronous on Biven's Arm, isolated pairs were
observed in both 1973 and 1975. Such isolation was never seen on Sea
Horse, in four years of observations.

96
Pre-Pair Formation Behavior
After arrival on Sea Horse the ibises fly to the mainland at
dawn and back to the island in the evening where they roost overnight
in areas removed from the sites of eventual nesting. The repeated
effort may provide the females with information influencing clutch
size. The large congregation of birds on the island may provide
stimulation for the development of scarlet coloration and the female
guiar pouch, as well as the actual onset of breeding activities.
The widely dispersed feeding grounds would be unsuitable for this
purpose.
Pair Formation-Aggression
In order to obtain a mate, the male White Ibis must establish
and repeatedly defend a display site to which he must also attract
mobile females. His success depends not only upon high levels of
aggression towards males, but also the eventual reduction of that
aggression when a suitable female approaches. The female's Head Rolling
behavior, with its resultant exposure of the large guiar pouch,
identifies her as a potential mate. This, combined with the sub
missive postures in her approach and interaction with the male, reduces
his aggressive tendencies and releases sexual behavior.
Female submission, while facilitating contact with the male,
would be inappropriate when competing with other females. Aggression
toward females occurs simultaneously with approaches of available males,
and no males, displaying or otherwise, are attacked at this time. The

97
guiar pouch and submissive postures of the female perhaps release
aggressive behavior in other females as well as sexual behavior in
males. This being true, there appears to be an added advantage to
directly facing the male when Head Rolling. If other females in the
area do not see the guiar pouch they may behave less aggressively,
allowing the properly-oriented female to remain closer to the male.
My data are insufficient to demonstrate that the female's orientation
affects other females in this way.
Analysis of Pair Formation Displays
Tinbergen (1952), Moynihan (1955), and Blest (1961) discuss the
modification (= ritualization) of behavior patterns and postures that
function as social signals. Displays originate, according to these
authors, as behaviors performed during conflict situations, for example,
during an aggressive encounter at a territorial boundary or at the
moment a pair-forming male sees a female approaching. At these times
the animal is motivated to perform antagonistic actions simultaneously;
in these examples, to attack and flee or to attack and mate. At such
times complete behavior patterns from neither source of motivation
are possible, and one of the following incomplete, ambiguous, or in
appropriate actions may occur: (1) Intention movement (after Daanje,
1950). These are the initial movements performed just prior to loco
motion. Intention movements for hopping in birds, for example, include
bending at the heel joint, lowering the breast, and drawing in the head
and neck. An animal in conflict may perform only these initial actions,
unable to locomote fully. (2) Redirected activities. An animal in

98
conflict, while unable to attack an opponent, will perform attack
behavior toward another object in the environment with which no
conflicting motivation is felt. The Grass-Pulling of Herring Gulls
(Larus argentatus) at the territorial boundary is a classic example
(Tinbergen, 1959). (3) Displacement activities. Some animals in a
conflict situation perform behaviors apparently irrelevant to the
situation (i.e.3 normally only observed when the animal is experienc
ing a different motivation from those in conflict). The preening
of the Avocet {Recurrir ostra americana) during aggressive encounters
is given by Tinbergen (1952) as an example.
These actions supply the raw materials from which displays
develop, through ritualization. According to Tinbergen (1952) these
conflict behaviors, having acquired a signal function, are modified
to reduce ambiguity. Characteristically, this process of modification
includes stereotyping of the behavioral components (often with
exaggeration and simplification of the original movements), development
of morphological features to enhance the conspicuousness of the signal,
and neurophysiological "emancipation" so that the modified behavior
is performed in the proper context relevant to its new function.
I believe more emphasis should be placed on the transfer of
information that is taking place before any ritualization occurs. In
order for a behavior pattern to become elaborated into a display, its
performance must provide a benefit from the very outset for both the
signaller and the signal receiver, or else selection will not favor
further development. Whether the behavior performed in a conflict
situation be labelled "intention movement" or "displacement activity"

99
it must provide information about the signaller that can be perceived
by and elicit a response from other individuals. When both participants
in a social encounter benefit from increased efficiency of the signals,
then any reduction in ambiguity is favored.
The displays of the White Ibis can be discussed within this
theoretical framework, including apparent origins of the behaviors
and the nature of the modifications that have taken place.
Snap Display (page 26). Individual elements of the Snap
display give indications of its origins. During nest building, males
gathering twigs extend their necks out and down, grasp a twig, and
shake it with both lateral bill movements and tugging. The scapular
feathers at this time are positioned variably, from compression to
full erection. These components are all found in the Snap display.
The duration of the neck extension during the Snap is longer
than the duration of bill thrusts; however, the speed of the extension
increases in the presence of a neighboring pair for the Snaps directed
toward it (and for these Snaps the scapular feathers are fully erected).
This suggests a second source of motivation for the Snap, that of in
hibited (and redirected) aggression.
Apparently both aggressive and nest building tendencies have
influenced the final expression of the Snap, reflecting the conflict
in motivations for the pair-forming male. The twig pulling component
is a common feature of the male's interactions with the female in
conflict situations. It is also seen in the Up-Down greeting display
and during pre-copulatory activities. Since the gathering of nest
material commences with the formation of the pair these twig pulling

100
components cannot be considered displacement activities. The pair
forming male is motivated to copulate and build a nest simultaneously,
and both of these are in conflict with his aggression.
Baerends and Van Der Cingel (1962) discuss the origin of the
Snap display of the Common Heron (Ardea cinrea). The form of the
display closely resembles the Snap of the ibis. They suggest that the
display originated in redirected aggression, when the female approached
an unmated male. The ambivalent behavior was a result of conflicting
tendencies to attack, flee, and perhaps "settle down" on the nest.
The authors disagree with Meyerriecks* (1960) conclusion that it
arises from displacement twig pulling.
Whereas the male White Ibis Snaps only when alone, unmated, and
advertising, the Common Heron male Snaps in response to repeated female
approaches. It is apparently not used as an advertisement in this
species and, therefore, may not communicate the same degree of sexual
motivation as it does for the ibis. In any case, it does appear that
sexual motivation (in the form of twig pulling behavior) contributes
to the Snap display.
The Snap is a distinctive pattern, immediately identifiable to
a human observer, but its performance has many highly-variable components.
The wings are either held at the sides or extended at the carpal joint
(a movement indicating aggressive-escape motivation in gulls, according
to Tinbergen, 1959) and sometimes twigs are grasped, as discussed above.
The form of the neck extension itself distinguishes the display? however,
Head Bobbing (discussed below) and orientation of the extensions toward
neighboring pairs are frequent variations. Tinbergen (1959) discusses

101
the adaptive significance of possessing several different displays
that communicate different levels of motivation, and he briefly
mentions the variations sometimes observed within a given display.
The Snap of the ibis appears to be more effective as a signal with
these variations than without. The neck extension itself attracts
females (and repels males) initially. The frequencies of associated
Head Bobbing, twig pulling, and wing extensions may then serve to
inform the female of the male's particular motivation levels. This
is the only advertisement he has, and it appears to be rich in infor
mation. The Head Bobbing seems correlated with low motivation (recall
the abandonment of display sites by two of the three Head-Bobbing
males) and the wing extension seems correlated with high levels of
aggression. The rate of performance is itself a variable parameter
that may reflect underlying levels of motivation.
Head Bobbing (page 27). Head Bobbing appears to be a low
intensity Snap display. Perhaps the bobbing motion indicates the
intention of neck extension while revealing the lack of sufficient
motivation to perform it completely. Head Bobbing males did not
extend their wings or pull at twigs, further indicating lack of
intensity.
Head Rolling (page 29). This pair formation activity is
clearly derived from the more extensive head rubbing motions employed
during preening. The rolling motion is common to both, but the rate
of performance is greater in pair-forming individuals and initial oil
extraction from the uropygial gland is absent. The display has quite
variable duration, angle of the bill while rolling, angle through which

102
the bill is rolled, and rate of performance. It appears little
modified from the original behavior, probably performed as a displace
ment activity by females motivated to approach and avoid displaying
males. The female's orientation toward the male and the resultant
exposure of the red guiar pouch are consistent components. It appears
as though selection has favored exposure of the pouch via the Head Roll,
but has not produced the stereotypy of the behavior pattern commonly
observed in displays. Stereotypy achieves a reduction of ambiguity
that in this case may have been unnecessary. A Head Rolling individual
with a large pouch can only be an unmated female. The pouch rapidly
disappears after pair formation and, once paired, females remain at
the nest site most of the time.
Display Preen (page 30). This action does not reflect any
obvious internal motivation and may function to increase conspicuousness
of the displayer by adding to the general increase in activity level
seen during pair formation.
Up-Down Greeting (page 32). The transitional behavior shown
by the four males (page 34) clarifies the origin of the Up-Down
greeting. For the male at this time the female is both an intruder
and a potential mate. Through Head Rolling and maintaining a head-down
and crouched posture, she eventually releases non-aggressive behavior.
The bill thrust is transformed into a slow and exaggerated arching
motion. Since the male mounts with the neck extended, the upward
extension of the neck in the greeting display may have originated as
a sexual component, namely, as an intention movement for mounting.
In the early conflict stages the male neither mounted nor attacked;

103
the greeting display was the resultant compromise. Twig pulling again
appears in a display that involves a conflict of mating and aggression
motivation.
In comparison with the herons and egrets on Biven's Arm, the most
conspicuous aspect of the White Ibises' pair formation is its simplicity.
The Snap of the male performs the necessary advertisement. The female's
Head Roll and associated guiar pouch provide the necessary sexual
identification. The herons employ several vocalizations and a variety
of aerial and stationary displays during pair formation. The number
of closely related sympatric heron species may account for the difference.
Historically, individual herons of similar but gentically incompatible
sympatric populations had to identify conspecifics. Those for whom
faulty communication resulted in fruitless interspecific pairing,
failed to make a contribution to the next generation. Selection favored
the development of unambiguous signals. The elaboration of several
displays for each species, identifying and isolating individuals in
it from the others, is the apparent result. The White Ibis has only
one close relative, the Scarlet Ibis (Eudocimus ruber) whose breeding
range is confined to South America. Without the disadvantages of
possible ambiguity, the simple signal system seems more desirable.
It attracts less attention from potential predators, conserves energy,
and involves a minimum of genetic information to both perform and
interpret the motor patterns. This simple sysem, then, probably
represents the primitive pattern in the order (see the discussion of
Comparisons Within the Order).

104
Pair formation is a process of mutual mate selection by male
and female. The male selects a site and displays. The female watches,
identifies herself, and approaches. The male accepts or rejects. The
female moves on or returns. The male chooses again. Even once accepted
(as shown by the Up-Down greeting) the female may leave without provo
cation or be driven off subsequently.
The investment that both the male and female are making in
terms of time and energy make such a mutual selection predictable
(see Trivers, 1972). The female must produce eggs, construct the nest,
and feed the young while the male obtains and defends the nest site,
gathers nest material (the most energetically expensive of the two
nest building roles), protects the female from promiscuous mating
attempts, and feeds the young. Of male attributes, it seems the
nature of the nest site selected, his level of aggression and his
performance of displays are the most obvious indicators of suitability
to the female, while perhaps the female's color intensity, pouch size
and level of aggression (submission) are indicators of suitability to
the male (particularly if they are correlated with the efficiency of
performance of other reproductive behaviors, such as nest building or
care of the young).
In each of four seasons on Sea Horse a flock of bathing
ibises was observed during the pair formation period. The only
V
explanation seems to be that the individuals constituting these flocks
are cleaning themselves prior to the mating attempt. In four inches of
water they land, wash and depart. Isolated bathing occurs throughout
the breeding season, but this concerted effort by so many is unique to

105
pair formation. It seems adaptive for an individual to remove any
soil from the white plumage that may reduce attractiveness.
The sequential analysis of male and female pair formation
displays (page 30) does not reveal any intimate association between
any actions. Apparently the displays of the male attract the female
initially but do not affect the timing of her activities. In all
cases the majority of male and female displays followed preening
or inactivity by the opposite sex.
Copulation
The behavioral elements of copulation differ little among birds.
Most, including many waterfowl, copulate on a stable perch or platform.
The male mounts, treads, lowers himself into position, depresses and
pumps the tail feathers, ejaculates, and dismounts. The female crouches
and remains motionless while raising her rectricies dorsally. The ibises'
pattern has a few unusual components, however. The male's pre-copulatory
twig pulling with his head and neck extended over the female's results
in a forced crouch by the female and a shift in the male's center of
gravity toward her. The ibis female cradles the male with her wings as
he descends, apparently increasing his stability. The grasping and
shaking of the male's bill by the female just prior to dismounting may
represent a communication to him that the cloacas are properly positioned
and release ejaculation. The inactivity of the female following copu
lation would seem to increase the chances for successful sperm
transport to the ova.

106
Of particular interest in this species is the rate of copulation.
For five days the pair copulates at a mean interval of every 73 minutes.
Assuming sperm transfer with each completed act, what is the function of
so much sperm? On Sea Horse only two eggs are produced and on Biven's
Arm only three. While the precise timing of fertilization is unknown,
surely all five days are not equally important.
Perhaps the ibises promiscuous mating has affected the copulation
rate. The male who discovers that his female has copulated with another
male has two choices. He can either break up the pair and form another
or he can flood the female with so much of his own sperm that he will
still be the likely father of the young. We must immediately eliminate
the possibility of acceptance of cuckolding, as such a non-productive
strategy would be strongly selected against. The male who drives off
his female loses time. Depending on the day of the copulation period in
which this occurs, he may have lost much of his color and the internal
readiness to display that accompanies it and require days to regain
both. The surrounding pairs would be out of phase and his young would
be hatched much later in the season.
If these considerations make this alternative untenable, then
repeated insemination may be the best compromise. The resultant in
creased demand for sperm could result in production of quantities
sufficient to allow some deposition in neighboring females.
The mild peaks in the daily copulation rate curve (Figure 6)
cannot be explained in terms of the timing of the feeding trips, since
both partners are present at the nest site. The mid-afternoon reduction
in activity is observed in all phases of reproduction (except perhaps

107
incubation) and the peaks at 1100 hours and 1700 hours may simply
reflect bursts of copulation prior to and following heat-induced in
activity.
The analysis of 63 intercopulatory intervals (Table 10) revealed
shorter intervals early in the copulation period. This probably
reflects the intensity of sexual motivation initially and, perhaps,
additional insurance for the male in counteracting early promiscuous
mating attempts.
Mating System
For every species, the mating system under which it operates is
a consequence of natural selection and, as such, will result in a
maximization of reproductive success for the individual. For most
avian species (> 90 per cent) this maximization is accomplished through
monogamy (Lack, 1968). Males and females, by restricting their activities
to one partner and the care of their offspring produce more young than
if they mated with more individuals and cared less for the young.
In order for another system to develop, such as polygamy or
promiscuity, one of the adults must be liberated from parental duties.
This is generally accomplished by a combination of precocial young
and richly abundant food supply. If the point is reached where a
female gains more of an advantage by pairing with an already paired
male than a single one (with perhaps poorer food supplies on his
territory for species that feed near the nest) the threshold of
polygyny is reached (Selander, 1972).

108
The ibis has hopelessly altricial young and, especially on
Sea Horse, must fly considerable distances to obtain food. Under
these conditions the assistance of both parents is essential for the
successful rearing of the young. Monogamy is expected and, whenever
a list has been compiled, the ibis has been called monogamous [e.g.,
Lack, 1968). However, the data show that following a monogamous pair
formation, males and females engage in a considerable amount of mutual
promiscuity.
The benefit of promiscuous mating for the male seems apparent.
He may be fortunate enough to father young he does not have to raise,
a favorable condition providing that the loss of sperm does not reduce
the likelihood of impregnating his own female. The adaptive significance
of this system for the female is less obvious. She invests a considerable
amount of time and energy selecting a mate based on qualities she per
ceives during the pair formation process, and then accepts sperm from
other males, presumably risking the loss of her mate's help. In the
absence of further data, several explanations for this female behavior
seem plausible: 1) Only nearby mated males approached females, suggest
ing that she may have been familiar with their individual characteristics
prior to the attempt. 2) Birds nesting in close proximity, with closely
synchronized cycles may represent extended families, introducing the
possibility of kin selection. Then females accepting nearby males
would be accepting gametes genetically similar to their mate's. How
ever, the mobility of some pairs following pair formation argues against
this possibility. A program of tagging over several seasons would
clarify this question. 3) Tables 14 and 15 show the reduced variability

109
of nest height, diameter, and tree species within the clusters. If
all the approaching males are from the same cluster, then they have
selected nest sites similar to the mate of the female. Since all
females were approached only by males in the same area and, con
sequently, from a nest site with many similar characteristics, the
disadvantage of accepting another male may be reduced if male nest
site preference is the criterion upon which the female bases her
selection of a mate (see the discussion of nest building). The
simplicity of the pair formation process for the ibis suggests that
the female may be selecting more on the basis of the quality of the
area the male has chosen. The Snap display may serve to inform the
female of a male's availability, followed by her close scrutiny of
the site he favors. Gilliard (1956) first discussed the idea of
transferral of female selection from the male to some inanimate object,
in his example, the bower of bowerbirds. Transferral to the nest site
has been suggested for the Long-billed Marsh Wren as well (Verner, 1965).
Perhaps, more accurately, the female may be choosing on the basis of
the male's observed ability to select a favorable area (or build a
suitable structure) rather than on the basis of his morphology or dis
plays. Site selection may be correlated with abilities during nest
building as well. 4) The female who accepts an interloping male and
is impregnated by him produces progeny who may inherit his stealth,
aggressiveness, and ability to form a pair (since all males involved
are paired). If these offspring in turn produce more young as a result,
then acceptance of the male is favored. A female who merely accepts
any male who approaches is receiving sperm from either an aggressive,

no
opportunistic interloper or, if he is thwarted, by a vigilant arid efficient
mate. If her partner cannot effectively prevent her promiscuity this
may constitute a shortcoming in the male that would be passed on to
their sons, consequently reducing their fitness. 5) The female may
also benefit from the insurance of multiple partners. All of the
females in this study copulated predominantly with their mates, and
he still seems to be the likely father of the young. In the event of
sterility, however, the promiscuous female could still produce a
viable clutch. The possibility of sperm competition should be
mentioned here as well.
In the absence of data on the relationship of the timing of in
semination to ovulation and the efficacy of sperm transfer and use in
promiscuous interactions, conclusions must be speculative. The extent
of male persistence at interrupting a partner's promiscuity, even though
this slows nest building,suggests that completed promiscuous copulations
are effective. This being the case, these data suggest an interesting
and complex selection process involving perhaps one or more of the
above considerations. The simultaneous selection for monogamous pair
bonding followed by mutual promiscuity is the apparent result.
I believe these considerations suggest a possible reevaluation of
the extent of monogamy among birds. The number of avian species that
are presently considered monogamous perhaps is inflated due to a lack
of extensive observation and quantification of copulations particularly
among species in which pairs nest in close proximity. Many studies of
breeding behavior emphasize pair formation activities, aggressive displays,
territoriality, nest building, etc., but deal with actual copulation only

Ill
briefly at best. This may reflect the amount of time spent by the
observer on this particular event, since the motor patterns of copu
lation are so similar from one avian species to another. Colonial
species, which have received much attention from field behaviorists,
would seem particularly susceptible to promiscuous mating due to the
ease with which potential mates can be approached. Also, high
densities would facilitate prior knowledge of partners by the female,
an important prerequisite for the model suggested here. Meanley (1955)
provided some quantification of the frequency of this phenomenon for
the Little Blue Heron when he reported 16 promiscuous mating attempts
in seven hours. Although he did not report the number of pairs he
was watching, his illustration (Figure 1, page 4) reveals an apparent
low density of nesting birds. He also mentioned that other heron
species shared the rookery. This suggests that he was observing a
limited number of pairs when these data were collected. If they were
based on five to 10 pairs of Little Blues, then promiscuous mating
attempts occurred every 2.2 to 4.4 pair-hours, compared to once every
5.3 pair-hours for the White Ibis in this study.
Nest Building
The whole process of nest site selection and construction is
crucial to the success of the mating effort. As with every other
aspect of the ibises' breeding behavior, the techniques employed
maximize the reproductive output for both sexes, or else they would
not exist.
Initially, the male must choose a potential site. On Sea
Horse the number of choices is enormous. Each year, however, the

112
order in which nesting areas were occupied was constant (see Figure
7). The western end of the main ridge was settled first. At this
point the trees of Gardner's Arm (the site of heron nesting) probably
afford maximum protection from northerly winds. The same species of
trees are present on the western end of the main ridge, as in the rest
of the hammock, although the habitat appears less dense. Perhaps the
reason for initial nesting here may be simply that the birds become
familiar with this area while they are roosting during the two weeks
prior to the commencement of breeding.
Once settlement here has begun, new nesters simply spread
eastward into suitable sites. The clearing and its human population
interrupts the flow and the eastern end beyond it is settled first.
The data on nest site parameters (Tables 12 and 13) show the
variability of the nest sites selected on Sea Horse and the comparative
similarity on Biven's Arm. This variation on Sea Horse gives the male
a wide range of choices. On Sea Horse the nests are higher because
the trees are taller. There seems to be no advantage to high nests.
In the absence of ground predators low nests are in little danger.
As the height increases the effect of the wind increases, and the
distance which the young may fall and must subsequently climb to
return increases. The chief predators are in the air and presumably
the higher the nest, the more conspicuous it is to these predators.
The limited data from 20 nests support this hypothesis: a greater
number of young survived to ten days in the lower nests (Table 23).
Table 13 reveals that oak trees held only 12.2 per cent of the nests
while constituting 25.9 per cent of the trees in the rookery,

113
while the bay trees held 67.1 per cent and only constituted 36.0 per
cent. The oakswerealso taller, and the mean height for a nest in
them was 18.0 feet compared with 11.6 for the bays. Perhaps this
is the reason for the comparative unpopularity of the oaks.
The diameter of the nest probably represents a compromise of
several factors. A small nest is less energetically expensive to
construct and less conspicuous. A large nest, however, provides
greater holding capacity for eggs and active young. The observed
size is an optimization of these parameters.
The degree of development of the understory would seem potentially
important if a young bird should fall from the nest. The clumsiness of
the nestlings and the jostling of a returning adult cause frequent
accidents. If there is sufficient vegetation for the young bird to
fall and climb upon, return to the nest is a possibility.
The nature of the sexual roles in nest construction is under
standable. The basic strategy of a mobile male gatherer and a stationary
female builder works efficiently, given the ibises' mating system. If
both sexes gathered material simultaneously, the nest would be pirated.
If the female collected while the male remained, it would be far more
difficult for the male to monitor her activities. The male stays
near the nest site to collect and returns frequently even without
material. Collecting nearby could be explained energetically, but
the expense of the male's constant returns without material argues
against energetics as the primary factor. This vigilance is success
ful in thwarting almost all promiscuous mating attempts and by so
doing, maintains the stability of the pair bond. If, through this

114
vigilance and repeated insemination the male could not be assured of
parenthood, the system would not continue.
The nest attentiveness during nest building is striking, especially
on Biven's Arm, where the males do not gather while the female is off
just prior to egg laying. Males on Sea Horse occasionally leave the
nest unguarded at this time. The greater competition for sticks on
Biven's Arm may explain this difference in attentiveness since the
main benefit of the male's affinity for the nest at this time is
probably the prevention of theft. Later, with eggs and young in the
nest, the adults of Sea Horse are the more attentive ones (with the
extent of avian predation the probable reason for the difference).
The differing strategies employed by males in the collection of
nest material deserves mention. Some begin construction soon after
pair formation and others wait until as late as 48 hours prior to the
first egg. Those that wait seem to run the risk of loss of the first
egg and lack of materials, but perhaps the avoidance of direct
competition for materials and the increased number of piratable nests
later on enhance the desirability of this approach.
Incubation
The alternation of incubating adults at the nest during incu
bation allows both sexes to feed daily while allowing for constant
attendance at the nest site. The temperature of the eggs is maintained
by rapid descent by the relieving bird onto the nest.
The quantitative data from the 1971 season show incubation to be
a complex behavior. Length of time on the eggs per hour is an apparent

115
function of environmental temperatures. In the early morning the
adults sit on the eggs for long periods and stand little. Correlated
with this, they rest with the bill buried in the back feathers, a
posture which retards heat loss across the skin of the face. As
temperature increases^ longer times off the nest, guiar fluttering and
erection of the back feathers occur, presumably to facilitate heat
loss. Though the bill even at this time may be placed on the back,
such timing of this behavior is rare. Late in incubation, the parent
not only rises frequently but also drops both wings, or the one closest
to the sun. This shading posture is the extreme behavioral adaptation
of the ibis for prevention of heat gain by the young as well.
Rain and wind also had the effect of increasing sitting time,
further indicating the importance of heat retention. As shown by the
14 and 15 May 1971 data (Figure 8), the depression of expected activity
at 1200 hours and the shady nature of the nests at this time suggests
the importance of micro-habitat.
The maintenance activities performed while incubating seem
predictable and adaptive. Preening of the breast is most common, as
would be expected. Almost all adults defecated only after deliberate
efforts to avoid fouling the nest site.
Hatching and Early Life
The increase in frequency of shading is an indication that
hatching is imminent. The actual process proceeds with no apparent
assistance by the adult. The removal of the eggshell presumably
functions to reduce conspicuousness of the nest although at this time

116
and until 10 days of age the nestlings are rarely left alone. De
composition of the organic matter adhering to the shell is a potential
problem also.
The narrow temperature range for the young is still maintained as
the parent shifts from sitting in an incubating posture to shading in
a crouched posture.
The high-pitched vocalization employed by the young when begging
is difficult for an observer to localize in the trees. Perhaps this
difficulty applies to predators as well.
When the young ibis is old enough to initiate feeding bouts by
hitting the adult, the pecks are oriented toward the distal 1/3 of the
bill. This is an area on many, though not all, of the adults that
retains a dark color, contrasting with the red of the facial skin and
proximal end of the bill. Perhaps this contrast facilitates locali
zation of the proper bill area by the young.
During the first 10 days, the continuation of adult alternation
at the nest is a compromise. It reduces the amount of food available
to the young, but it assures vigilance by a parent and temperature
control during the early life of the young, when homeothermy is probably
not yet efficient. At 10 days, when the adults discontinue their vigil,
the young are too large for any local predators and capable of tempera
ture control. The tenth day of the nestlings' lives is a critical one.
By this time they have gained mobility and can cross to nearby nests;
with that ability comes the possibility of an adult feeding someone
else's young. It is not surprising that individual recognition of
young by the adults develops by 10 days. Strange young discovered in

117
the nest by adults are attacked. This is not the case for smaller
young. It rarely occurs and perhaps there has been no selection
favoring recognition at a younger age. At 10 days the young must
also cope with temperature extremes and predators. Their response
to human predators changes from crouching in the nest to attempted
escape at about this age, and it does not seem adaptive on Sea Horse.
They move to the branches' end and leap while the predator is still
several feet away. This departure is fatal unless a very dense under
story or low nest site permits re-entry. Perhaps in more typical
ibis nesting habitat such as the dense stands of mangrove in South
Florida, premature departure from the limb by the young is not so
extreme a behavior since return to the nest from below is easier.
After the ten day change in adult attentiveness, the development
of the young is straightforward. As mobility increases, the adults
begin landing farther away and moving off after feeding the young
briefly. This encourages the young to follow, as strength and balance
improve. The pursuit flight is the culmination of this training by
the adult. The young bird must pursue the adult after each feed in
order to be fed again, learning through short flights the skills
necessary for eventual migration. The added energy expenditure for
what appears to be reduced food is compensated for somewhat by feed
ing of the young bird itself as a member of the all-young flocks that
probe for crabs on the mud flats on Sea Horse. As the adult contri
bution declines this source of food increases.
In these feeding flocks the young show aggression when a localized
food source is available. Free ranging flocks show bill thrusting,

118
harsh vocalizing and turning away indistinguishable from the behavior
of my artificially fed flocks (p. 78). The density of food particles
in the feeding situation I created is different from the usual wild
condition. On the mud flats the crabs are scattered and conflicts
are rare. Since these flocks of young apparently consist of the same
individuals each day, there is a potential for the development of a
linear dominance hierarchy of the type seen under the artificial con
ditions, which could potentially be useful if food sources become
scarce and competition increases.
Another possible application of this capacity for individual
recognition and establishment of dominance is during the adult feedings
in the treetops. Here young are observed supplanting others and
obtaining conspicuous roosts. If visibility increases as a function
of roost site then the efficiency of parent-young location would increase.
Nest mates competing for food from the same parent may also determine
access by a limited hierarchy of two or three individuals.
The loose flocks of the feeding ibises provide many eyes and
ears for potential predators in the open habitat of the marsh and grass
flats. Local concentrations of invertebrates are more efficiently
discovered by a mobile, probing group of birds than by individuals.
Unlike the slow, deliberate stalking of the herons, the ibis feeds in
constant motion: probing, withdrawing and relocating the bill.
The tidal effects on feeding intensity are obvious; the prey is
only accessible up to approximately four inches of water. The flocks
of young also show a distinct recession of feeding activities in the
afternoon, even at low tide, suggesting a temperature effect (their
dark plumage may facilitate overheating).

119
Comparisons Within the Order
The degree of behavioral similarity between the storks and the
White Ibis suggests that they are more closely related to each other
than either one is to the herons. Even the elaborate displays of the
Marabou Stork apparently have their origin in the simple patterns of
the Openbills and the Wood Storks. The displays of the White Ibis bear
the closest resemblance to those of the latter two groups, particularly
the greeting and ritualized fighting. However, generalizations concern
ing all of the ibises must await further research.
The Snap display of the herons does appear quite similar to the
Snap of the White Ibis, and this is the pattern conspicuously absent
among the storks. However, the Swaying Twig Grasping of the storks
may well represent the ancestral pattern from which the Snap arose.
Twig pulling is associated with the Snap in both the herons and the
White Ibis, and the constant directional changes of the ibis are not
unlike the "sway" seen in the stork display. The Openbilled Storks'
Advertising Sway also has this oscillation as a component, is employed
in the same context as the White Ibises' Snap, and is derived from
Swaying Twig Grasping. Whereas the Snap of the herons resembles the
ibises', it is performed in a different context.
The proliferation of aerial displays and vocalizations of the
herons is not seen in either the storks or the White Ibis. It is
suggested elsewhere that these may have developed as behavioral
isolating mechanisms. The nature of the behaviors indicates that they
may have evolved in a dense habitat in which visibility was reduced,
necessitating the development of aerial maneuvers and vocalizations.

120
The simplicity of and the similarity between the behavioral
repertoires of the White Ibis, Openbills, and Wood Storks indicates
that they have been least modified from the ancestral condition. Kahl
(1972e) lumps the Openbills and Wood Storks together into one tribe
in recognition of their behavioral affinities.

SUMMARY
White Ibises begin arriving at Sea Horse Key in early March.
Their numbers increase over several weeks, with flocks arriving in the
late afternoon and departing for the mainland at daybreak. Activity
at Biven's Arm does not begin until April.
Breeding begins on Sea Horse Key when several hundred birds
remain on the island at dawn. Flocks move over the trees, roosting
briefly in several areas. By noon of the first day males begin to
select display sites and defend them with aggressive behaviors, in
cluding the Forward Threat, the Stab-and-counter Stab Ritual, and
overt fighting.
Once a small display site has been secured, the male begins
performing pair formation activities, including the Snap Display,
Head Bobbing, Head Rolling, Display Preening, preening and feather
ruffling. Females, in response to the behavior of the males, land
nearby and perform Head Rolling, Display Preening, preening and feather
ruffling. They also behave aggressively toward other females.
After displaying for several minutes, the female attempts to
land next to the male, approaching with her head down and plumage
compressed. The male initially responds aggressively, driving off
the female with bill thrusts. Her eventual acceptance by the male
is demonstrated by performance of the Up-Down Greeting Display. The
female may subsequently leave or be driven from the display site. The
first copulation marks the formation of the pair.
121

122
All copulations of the pair occur at the nest site at a mean rate of
once every 73 minutes for five days. During this time the males and
females in a nesting cluster engage in mutual promiscuity. Nearby
mated males approach a mated female when her mate is off gathering
nest material. Only 12 of 62 attempts were apparently successful,
however, due to the vigilance of males, who gather material in close
proximity to the nest site. Both males and females apparently benefit
from this mating system and the explanation presented in the Discussion
may be applicable to many other avian species, especially those nesting
colonially.
Only the male gathers nest material, and the female is the
primary builder. Males pirate material from adjacent unguarded nests.
Nests from the previous year are built upon or dissected.
Nesting on Sea Horse Key occurs in a regular pattern, beginning
on the western end of the hardwood hammock and moving eastward. Only
trees within the hammock are selected, and nests are constructed at
heights from 2.5 to 40 feet. Groups of five to 20 pairs begin copu
lation and nest building in synchrony. The nests within a cluster
show similarities for such parameters as height, diameter, species of
tree, and nature of the understory.
On Sea Horse Key the herons and egrets nest on another part of
the island, whereas on Biven's Arm the ibises, herons, and egrets nest
in close proximity.
The first egg is laid on the fifth day of copulation. The clutch
size on Sea Horse Key was less than 2.2 in each of the four seasons of
the study. On Biven's Arm it was greater than 2.8 early in the season.

123
This difference is apparently the result of the greater distance the
adults on Sea Horse Key must fly to obtain food (greater than three
miles, compared to 1.5 miles for Biven's Arm adults) and the associated
reduction in feeding rates of the young on the island.
Incubation begins with the completion of the clutch and adults
alternate at the nest site. Attentiveness to the nest varies with
environmental conditions. The incubation period is 21 days.
The young are fed by direct regurgitation and are attended by
one of the parents at all times until 10 days old, while the other
parent gathers food (primarily crustaceans and insects). Prior to
10 days of age, the young are susceptible to predation from Fish Crows
and Black-crowned Night Herons. At four weeks the young can fly
short distances. At five weeks they no longer return to the nest site,
but are fed in the tree tops. Independence is achieved in seven weeks.
The young ibises are capable of establishing linear dominance hierarchies
in all-young feeding flocks. These flocks are active primarily at low
tide in the morning and evening hours.
The courtship activities of the White Ibis most closely resemble
those of the Openbilled and Wood Storks. Heron courtship is characterized
by a greater number of activities, most of which have no apparent
homologue in the White Ibis or the storks.

PLATES

Plate la. Female ibis, with guiar pouch well developed
Plate lb. Male ibis, with guiar pouch poorly developed

125

Plate 2a.
Forward threat.
Plate 2b. Biven's Arm rookery.

127

Plate 3a. Stab-and-counterstab (1).
Plate 3b. Stab-and-counterstab (2).


Plate 4a. Submissive posture.
Plate 4b. Snap display.

131

Plate 5a. Head rolling.
Plate 5b
Neck crossing pre-copulatory activity.

133

Plate 6a. Basin bathing flock.
Plate 6b. Male and female stance at the nest.

135

Plate 7a. Male mounting female.
Plate 7b. Male treading (with back feathers erected).

137

Plate 8a. Male descended -
ill positions.
Plate 8b. Female cradling male, male tail depressed.

139

Plate 9a. Female bill shaking.
Plate 9b. Adult shading.

141

Plate 10a.
Young begging orientation.
Plate 10b.
Young receiving food.

143

LITERATURE CITED
Baerends, G. P., and N. A. Van Der Cingel. 1962. On the phylogenetic
origin of the Snap Display of the Common Heron (Ardea cinevea L.).
Symp. Zool. Soc. Lond. 8: 7-24.
Beebe, W. C. 1914. Notes on the ontogeny of the White Ibis, Guara
alba, Zoolgica 1: 240-248.
Blaker, D. 196 9. Behaviour of the Cattle Egret Ardeola ibis.
Ostrich 40: 75-129.
Blest, A. D. 1961. The concept of ritualization. Pp. 102-124 in
Current Problems in Animal Behavior (W. H. Thorpe and 0. L.
Zangwill, Eds.) Cambridge Univ. Press.
Daanje, A. 1950. On locomotory movements in birds and the intention
movements derived from them. Behaviour 3: 48-99.
ffrench, R. P., and F. Haverschmidt. 1970. The Scarlet Ibis of
Surinam and Trinidad. Living Bird 9: 146-165.
Gilliard, E. T. 1956. Bower ornamentation versus plumage characters
in bowerbirds. Auk 73: 450-451.
Kahl, M. P. 1966. Comparative ethology of the Ciconiidae. Part 1.
The Marabou Stork, Leptoptilos crumeniferus (Lesson). Behaviour
27: 76-106.
Kahl, M. P. 1972a. Comparative ethology of the Ciconiidae. Part 2.
The Adjutant Storks, Leptoptilos dubius (Gmelin) and L. javanicus
(Horsfeld). Ardea 60: 97-111.
Kahl, M. P. 1972b. Comparative ethology of the Ciconiidae. The Wood
Storks (genera Myoteria and Ibis). Ibis 114: 15-29.
Kahl, M. P. 1972c. Comparative ethology of the Ciconiidae. Part 4.
The "typical" storks (genera Ciconia, Sphenorhynohus, Dissoura,
and Euxenura). Zeit. Tierpsychol. 30: 225-252.
Kahl, M. P. 1972d. Comparative ethology of the Ciconiidae. Part 5.
The Openbilled Storks (genus Anastomus). J. fur Ornithologie
113: 121-137.
Kahl, M. P. 1972e. A revision of the family Ciconiidae (Aves). J.
Zool. Soc. Lond. 167: 451-461.
144

145
Kahl, M. P. 1973. Comparative ethology of the Ciconiidae. Part 6.
The Blacknecked, Saddlebill, and Jabir Storks (genera Xenorhynohus,
Ephippiorhynchus, and Jabir). Condor 75: 17-27.
Lack, D. 1968. Ecological adaptations for breeding in birds. London,
Methuen and Co., Ltd.
Lancaster, D. A. 1970. Breeding behavior of the Cattle Egret in
Colombia. Living Bird 9: 167-194.
Meanley, B. 1955. A nesting study of the Little Blue Heron in
eastern Arkansas. Wilson Bull. 67: 84-99.
Meyerriecks, A. J. 1960. Comparative breeding behavior of four species
of North American herons. Pub!. Nuttall Ornith. Club 2: 1-158.
Moynihan, M. 1955. Remarks on the original sources of displays. Auk
72: 240-246.
Nesbitt, S. A., W. M. Hetrick, and L. E. Williams. 1975. Foods of the
White Ibis from seven collection sites in Florida. Proc. 28th
Conf. Southeastern Assoc, of Game and Fish Commissioners (in
press).
Palmer, R. S. (Ed.) 1962. Handbook of North American Birds, Volume 1.
New Haven, Yale Univ. Press.
Selander, R. K. 1972. Sexual selection and dimorphism in birds. Pp.
180-230 in Sexual Selection and the Descent of Man (B. Campbell,
Ed.). Chicago, Aldine.
Skead, C. T. 1951. A study of the Hadedah Ibis Hagedashia h.
hagedash. Ibis 93: 360-382.
Tinbergen, N. 1952. "Derived" activities; their causation, biological
significance, origin, and emancipation during evolution. Quart.
Rev. Biol. 27: 1-32.
Tinbergen, N. 1959. Comparative studies of the behavior of gulls
(Laridae): a progress report. Behaviour 15: 1-70.
Tinbergen, N., and R. A. Hinde. 1958. The comparative study of species-
specific behavior. Pp. 251-268 in Behavior and Evolution (A. Roe
and G. G. Simpson, Eds.). New Haven, Yale Univ. Press.
Trivers, R. L. 1972. Parental investment and sexual selection. Pp.
136-159 in Sexual Selection and the Descent of Man (B. Campbell,
Ed.). Chicago, Aldine.
Verner, J. 1965. Breeding biology of the Long-billed Marsh Wren.
Condor 67: 6-30.

146
Wharton, C. 1958. The ecology of the cottonmouths Agkistrodon
piscvoras piscivorus Lacepede of Sea Horse Key, Florida.
Ph.D. dissertation, Gainesville, Florida, Univ. of Florida.

BIOGRAPHICAL SKETCH
Thomas James Rudegeair, Jr. was born in Philadelphia, Pennsylvania
on October 31, 1948. He grew up and attended high school in Mt. Holly,
a small town near the New Jersey pine barrens. He first learned of
animals from the hardwood and pine forests near his home and the ocean
and estuary he visited every summer.
He received his B.A. in Biology from the University of Delaware
in 1970 and began graduate work in Zoology at the University of Florida
in the same year.
147

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
JP
fofessor of Zoology
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is fully
adequate, in scope and quality, as a dissertation for the degree of
Doctor of Philosophy.
Professor of Entomology
This dissertation was submitted to the Graduate Faculty of the Department
of Zoology in the College of Arts and Sciences and to the Graduate Council,
and was accepted as partial fulfillment of the requirements for the degree
of Doctor of Philosophy.
March, 1975
Dean, Graduate School



77
As the days pass, the mobility of the young increases and tne.y
venture farther from the nest site. At about age four weeks they
have attained minimum flight ability and cross short distances between
branches. At this age they return quickly to the nest site while
vocalizing, when the parent returns. If the young fail to return,
the adult looks around and, within a minute, begins to utter single
soft honks. By five weeks of age the young never return to the nest
site but, instead, remain roosted in the treetops. The adults land
in the area and generally are approached immediately by the young
birds. Occasionally the young fly to the wrong adult and are attacked
with bill thrusts. The response of the young is the same as that of
a submissive adult--a quick turn away from the aggressor with compressed
plumage. This response terminates the adult's attack.
When the right adult and young are matched in the treetops, a
period of intense activity ensues. While the young seven days old
initiate feeding, by five weeks their size, strength and eagerness are
almost overpowering. The adult turns away as the young bird approaches
and often extends its wings for balance. The young beat their wings
and vocalize while hitting the parents bill with their own. At an
age of two weeks the nestlings place one wing over the back of the adult
and by five weeks this exerts a considerable restraining influence. The
young are fed by the same regurgitation process for the same three to
10 second interval but only to a maximum of three times at any one perch.
Then the adult flies, usually several feet away, and the young follow.
At the new roost the process may be continued.


120
The simplicity of and the similarity between the behavioral
repertoires of the White Ibis, Openbills, and Wood Storks indicates
that they have been least modified from the ancestral condition. Kahl
(1972e) lumps the Openbills and Wood Storks together into one tribe
in recognition of their behavioral affinities.


Table 3. Mean ambient temperatures for the months preceeding breeding. Date of
the first observed copulation and the mean temperature for the 6 days
preceeding it are also given. Climatic data in F are courtesy of the
U. S. Department of Commerce, Natural Oceanic and Atmospheric Admin
istration (Apalachicola Station).
Year
Jan.
Feb. 1-14
Feb. 15-28
Mar. 1-15
Mar. 16-31
Apr. 1-15
6 Days
Before First
Copulation
Date of
First
Copulation
1971
53.8
49.2
59.8
57.1
59.3
63.1
67.3
17 Apr
1972
58.6
51.4
58.4
59.6
64.6
67.9
64.7
20 Mar
1973
55.0
53.4
52.8
66.3
62.9
63.5
64.2
31 Mar
1974
65.6
59.1
55.1
65.8
61.9
68.2
63.0
28 Mar


96
Pre-Pair Formation Behavior
After arrival on Sea Horse the ibises fly to the mainland at
dawn and back to the island in the evening where they roost overnight
in areas removed from the sites of eventual nesting. The repeated
effort may provide the females with information influencing clutch
size. The large congregation of birds on the island may provide
stimulation for the development of scarlet coloration and the female
guiar pouch, as well as the actual onset of breeding activities.
The widely dispersed feeding grounds would be unsuitable for this
purpose.
Pair Formation-Aggression
In order to obtain a mate, the male White Ibis must establish
and repeatedly defend a display site to which he must also attract
mobile females. His success depends not only upon high levels of
aggression towards males, but also the eventual reduction of that
aggression when a suitable female approaches. The female's Head Rolling
behavior, with its resultant exposure of the large guiar pouch,
identifies her as a potential mate. This, combined with the sub
missive postures in her approach and interaction with the male, reduces
his aggressive tendencies and releases sexual behavior.
Female submission, while facilitating contact with the male,
would be inappropriate when competing with other females. Aggression
toward females occurs simultaneously with approaches of available males,
and no males, displaying or otherwise, are attacked at this time. The


89
to the neck arching,the Marabou Stork throws its head further back and
bill clatters, and the "typical" storks, while showing considerable
variation, are all more elaborate than the ibis and the Openbills.
The Up-Down is performed as a greeting in all species. No display
resembling this has been described for the herons.
All of the storks and the White Ibis perform copulatory bill
shaking. The stork male always performs the Copulation Clattering
while the female does the Bill Shaking during copulation of the White
Ibis. No copulatory bill shaking of any kind has been described for
the herons.
The Wood Storks and the White Ibis perform Display Preening, and
from Kahl's description (1972b) both do it the same, by running the bill
along the outer edge of the wing. The Wing Touch of the Cattle Egret,
as described by Blaker (1969) sounds very similar to this pattern, but
no comparable display is described for the other herons.
The two major pair formation displays of the White Ibis, Head
Rolling and the Snap display, have no precise equivalents among the
stork displays. The storks do show the unritualized head rubbing that
constitutes Head Rolling, but there is no mention of an increase in its
performance during pair formation. Kahl (1966) describes a Snap display
but it is unlike the Snap of the ibis. It involves merely a bill gape
from an erect posture. However, the Swaying Twig Grasping of the Open-
bills, Wood Storks, and Marabou Stork (for which it is most highly
stereotyped) resembles the ibises' Snap. In this display, unmated or
newly mated males bend forward and lightly grasp twigs. Frequently
the male turns (= sways) his body through as much as 80 degrees between
performances, much as the ibis male does during the Snap display.


30
Oriented as she is, the Head Roll of the female exposes her
guiar region to the male that she is watching.
Display Preen (after Kahl, 1972a, for Wood Storks, e.g
Mycteria americana; similar to the Wing Touch described by Blaker, 1968,
for the Cattle Egret). During Display Preening, the bird runs its
bill along the outside edge of the wing, with the wing held briefly
away from the side. It appears as normal preening except that the
bill is often out of contact with the wing feathers. The pair-forming
male shows this behavior 2.5 times/min (n = 157; s = 1.5) and the
pair-forming female 2.2 times/min (n = 160; s = 1.5).
Preening and Feather Ruffling. As shown in Table 4, both
male and female perform preening and feather ruffling intermittently
with the above behaviors. Displaying birds are moving constantly and
rates of performance for these movements are high when compared to
rates for roosting birds not forming pairs. These latter individuals
preen briefly, usually for less than one minute, followed by long
periods of inactivity. Incubating birds, for example, execute a mean
number of 2.6 preening episodes/hour. Males that begin displaying in
an area and are not approached by any females within one to two hours
discontinue this intense activity and then abandon the site. The
rates of performance of displays differ from year to year on Sea Horse
and between Sea Horse and Biven's Arm. Table 5 shows some of these
data.
Table 6 gives a sequential analysis of the main activities of
the male and female during active displaying. All activities were
recorded simultaneously to determine possible cause and effect


139


54
Table 12. Nest site data. Overall values for Sea Horse
Key and Biven's Arm for nest height, diameter,
and nearest neighbor.
Nest Parameter
Sea Horse
Mean s
n
Biven1s
Mean
Arm
s
n
Height
12.0 ft.
5.3
999
5.9 ft.
1.9
83
Diameter
10.0 in.
1.9
1051
10.1 in.
1.2
78
Nearest Neighbor
3.8 ft.
3.7
1052
1.8 ft.
1.4
72


Ill
briefly at best. This may reflect the amount of time spent by the
observer on this particular event, since the motor patterns of copu
lation are so similar from one avian species to another. Colonial
species, which have received much attention from field behaviorists,
would seem particularly susceptible to promiscuous mating due to the
ease with which potential mates can be approached. Also, high
densities would facilitate prior knowledge of partners by the female,
an important prerequisite for the model suggested here. Meanley (1955)
provided some quantification of the frequency of this phenomenon for
the Little Blue Heron when he reported 16 promiscuous mating attempts
in seven hours. Although he did not report the number of pairs he
was watching, his illustration (Figure 1, page 4) reveals an apparent
low density of nesting birds. He also mentioned that other heron
species shared the rookery. This suggests that he was observing a
limited number of pairs when these data were collected. If they were
based on five to 10 pairs of Little Blues, then promiscuous mating
attempts occurred every 2.2 to 4.4 pair-hours, compared to once every
5.3 pair-hours for the White Ibis in this study.
Nest Building
The whole process of nest site selection and construction is
crucial to the success of the mating effort. As with every other
aspect of the ibises' breeding behavior, the techniques employed
maximize the reproductive output for both sexes, or else they would
not exist.
Initially, the male must choose a potential site. On Sea
Horse the number of choices is enormous. Each year, however, the


45
alone on a nest site and no male traveled more than 15 feet to
attempt copulation. All 15 promiscuous males known to me were already
paired, as were all 16 females. While 15 males were observed in the
pair formation period, none was ever seen approaching nearby paired
females. The most promiscuous female copulated with her mate 63% of
the time (7 of 11), followed by a female who did so 85% of the time
(17 of 20).
The female continues to return to the nest site with her neck
extended and head down throughout the copulation period.
The duration of the greeting display is reduced by the second
day of copulation, as the males frequently arrive and depart with nest
material. Vocalizations become more brief, and often are not given
at all. By the fourth day of copulation and thereafter, the greeting
display is reserved for the return of one of the pair following an
extended absence from the nest. By this time also, the sexual difference
in the pitch of the vocalizations given by each sex during the greeting
has disappeared.
On Sea Horse, the female leaves the nest site for several hours
on the third or fourth day of copulation apparently to feed, as some
are observed flying toward the mainland. During the females absence,
the male usually remains at the nest site. Infrequent departures by
the male occur, and at these times any construction already completed
at the nest site is in jeopardy. Biven's Arm males never leave the
nest unguarded at this time. When the female returns to Sea Horse,
she remains at the nest site until the first egg is laid on the fifth
day of copulation, performing her duties as primary nest builder. The


106
Of particular interest in this species is the rate of copulation.
For five days the pair copulates at a mean interval of every 73 minutes.
Assuming sperm transfer with each completed act, what is the function of
so much sperm? On Sea Horse only two eggs are produced and on Biven's
Arm only three. While the precise timing of fertilization is unknown,
surely all five days are not equally important.
Perhaps the ibises promiscuous mating has affected the copulation
rate. The male who discovers that his female has copulated with another
male has two choices. He can either break up the pair and form another
or he can flood the female with so much of his own sperm that he will
still be the likely father of the young. We must immediately eliminate
the possibility of acceptance of cuckolding, as such a non-productive
strategy would be strongly selected against. The male who drives off
his female loses time. Depending on the day of the copulation period in
which this occurs, he may have lost much of his color and the internal
readiness to display that accompanies it and require days to regain
both. The surrounding pairs would be out of phase and his young would
be hatched much later in the season.
If these considerations make this alternative untenable, then
repeated insemination may be the best compromise. The resultant in
creased demand for sperm could result in production of quantities
sufficient to allow some deposition in neighboring females.
The mild peaks in the daily copulation rate curve (Figure 6)
cannot be explained in terms of the timing of the feeding trips, since
both partners are present at the nest site. The mid-afternoon reduction
in activity is observed in all phases of reproduction (except perhaps


Plate 3a. Stab-and-counterstab (1).
Plate 3b. Stab-and-counterstab (2).


LIST OF FIGURES
Figure Page
1 Sea Horse Key and surrounding area 4
2 Sea Horse Key (vegetation) 6
3 Number of ibises arriving through the day at
Sea Horse: 14 March 1974 (pre-pair formation) 20
4 Profile of a White Ibis flock in flight 22
5 Sea Horse Key approach routes and favored roosts 23
6 Copulations per hour 42
7 Sea Horse Key map of nesting areas and the order
of settlement of island areas 48
8 Minutes off the eggs (inattentiveness) during
incubation vs. time of day; temperature vs. time
of day 61
9 Minutes off the eggs during incubation vs. day
of incubation 62
10Young in the basin at Sea Horse vs. time
of day 81
vi i


104
Pair formation is a process of mutual mate selection by male
and female. The male selects a site and displays. The female watches,
identifies herself, and approaches. The male accepts or rejects. The
female moves on or returns. The male chooses again. Even once accepted
(as shown by the Up-Down greeting) the female may leave without provo
cation or be driven off subsequently.
The investment that both the male and female are making in
terms of time and energy make such a mutual selection predictable
(see Trivers, 1972). The female must produce eggs, construct the nest,
and feed the young while the male obtains and defends the nest site,
gathers nest material (the most energetically expensive of the two
nest building roles), protects the female from promiscuous mating
attempts, and feeds the young. Of male attributes, it seems the
nature of the nest site selected, his level of aggression and his
performance of displays are the most obvious indicators of suitability
to the female, while perhaps the female's color intensity, pouch size
and level of aggression (submission) are indicators of suitability to
the male (particularly if they are correlated with the efficiency of
performance of other reproductive behaviors, such as nest building or
care of the young).
In each of four seasons on Sea Horse a flock of bathing
ibises was observed during the pair formation period. The only
V
explanation seems to be that the individuals constituting these flocks
are cleaning themselves prior to the mating attempt. In four inches of
water they land, wash and depart. Isolated bathing occurs throughout
the breeding season, but this concerted effort by so many is unique to


105
pair formation. It seems adaptive for an individual to remove any
soil from the white plumage that may reduce attractiveness.
The sequential analysis of male and female pair formation
displays (page 30) does not reveal any intimate association between
any actions. Apparently the displays of the male attract the female
initially but do not affect the timing of her activities. In all
cases the majority of male and female displays followed preening
or inactivity by the opposite sex.
Copulation
The behavioral elements of copulation differ little among birds.
Most, including many waterfowl, copulate on a stable perch or platform.
The male mounts, treads, lowers himself into position, depresses and
pumps the tail feathers, ejaculates, and dismounts. The female crouches
and remains motionless while raising her rectricies dorsally. The ibises'
pattern has a few unusual components, however. The male's pre-copulatory
twig pulling with his head and neck extended over the female's results
in a forced crouch by the female and a shift in the male's center of
gravity toward her. The ibis female cradles the male with her wings as
he descends, apparently increasing his stability. The grasping and
shaking of the male's bill by the female just prior to dismounting may
represent a communication to him that the cloacas are properly positioned
and release ejaculation. The inactivity of the female following copu
lation would seem to increase the chances for successful sperm
transport to the ova.


115
function of environmental temperatures. In the early morning the
adults sit on the eggs for long periods and stand little. Correlated
with this, they rest with the bill buried in the back feathers, a
posture which retards heat loss across the skin of the face. As
temperature increases^ longer times off the nest, guiar fluttering and
erection of the back feathers occur, presumably to facilitate heat
loss. Though the bill even at this time may be placed on the back,
such timing of this behavior is rare. Late in incubation, the parent
not only rises frequently but also drops both wings, or the one closest
to the sun. This shading posture is the extreme behavioral adaptation
of the ibis for prevention of heat gain by the young as well.
Rain and wind also had the effect of increasing sitting time,
further indicating the importance of heat retention. As shown by the
14 and 15 May 1971 data (Figure 8), the depression of expected activity
at 1200 hours and the shady nature of the nests at this time suggests
the importance of micro-habitat.
The maintenance activities performed while incubating seem
predictable and adaptive. Preening of the breast is most common, as
would be expected. Almost all adults defecated only after deliberate
efforts to avoid fouling the nest site.
Hatching and Early Life
The increase in frequency of shading is an indication that
hatching is imminent. The actual process proceeds with no apparent
assistance by the adult. The removal of the eggshell presumably
functions to reduce conspicuousness of the nest although at this time


Detailed observations were discontinued at nightfall, but
extensive vocalizations and wing flapping were audible throughout the
night and indicate that at least greetings at the nest site were
taking place at night during the pair formation period.
Whereas flocks of feeding ibises are a common sight at low
tide on Sea Horse Key, a unique phenomenon occurs during the first
few days of pair formation. In 1971 on the south shore, and in 1972,
1973, and 1974 in the basin on the island's north side, flocks of 20
to 100 individuals were observed standing in three to five inches of
water, with less than 10% of the birds feeding (and, more commonly, with
no birds feeding) (Plate 6a). These flocks were open with recruits
arriving and residents departing every few seconds. Arriving birds
invariably landed within three feet of another individual, but the
latter showed no reaction. Occasional single bill thrusts were seen
between individuals that came within a foot of each other, but no
extended aggression occurred. The principal activities of the birds
were: (1) head dipping (approximately 6/min), which consisted of a
lowering of the head into the water and then raising up, sending a wave
of water over the back; in 25% of the cases (n = 72) this was accomplished
by an initial extension of the neck out and downward, a behavior pattern
strongly resembling the Snap; (2) head shaking (approximately 1/min)
following the wetting process; (3) feather shaking (0.5/min) performed
with the legs flexed, resulting in splashing water over the wings and
back; (4) preening (2.0/min). An individual would typically arrive
without incident, dip its head into the water one or more times, shake
the feathers for 10 to 60 seconds, preen and depart. Most individuals


125


BIOGRAPHICAL SKETCH
Thomas James Rudegeair, Jr. was born in Philadelphia, Pennsylvania
on October 31, 1948. He grew up and attended high school in Mt. Holly,
a small town near the New Jersey pine barrens. He first learned of
animals from the hardwood and pine forests near his home and the ocean
and estuary he visited every summer.
He received his B.A. in Biology from the University of Delaware
in 1970 and began graduate work in Zoology at the University of Florida
in the same year.
147


35
30
25
20
15
10
5
I
0600
o o
i A
9 July
10 July
16 July
\
LT
1
0800
1000 1200 1400
Hours
1600
1800
2000
10. Young feeding in basin vs. time of day (and tide level).


METHODS
Because Sea Horse Key is a National Wildlife Refuge, working
within the hammock is discouraged. Throughout the breeding season
the adult ibises are extremely wary. During pair formation nest sites
are readily abandoned, and later in the season eggs and young are left
exposed to Fish Crows and Night Herons for at least several minutes,
if the adults are disturbed. As a result, all of my observations were
taken from at least 50 feet with the aid of 7 X 50 and 7-15 X 50 zoom
binoculars. I observed from the edge of the trees and from the catwalk
around the lighthouse tower situated in the center of the clearing on
the crest of the main ridge. The tower is built into a large house that
has windows which afforded closer observations of many activities,
although their low position made observation of the nest contents
impossible. Tripods were employed on the tower and from the windows,
and various behaviors were recorded with a Bolex 250 Macrozoom (8:1)
super-8 mm movie camera and a Mamiya/Sekor 1000 DTL 35 mm single lens
reflex camera, with either a 400 mm or 900 mm telephoto lens attached.
Notes were taken on both a Norelco Cassette Recorder and by hand, often
with the aid of assistants. Stop watches were used to determine the
duration of behaviors, and a wrist watch to record the time of day.
During incubation, thermometers and a three-lead theromgraph were used
to determine ambient temperatures in the study area.
Clutch sizes were obtained by single trips through the rookery
each year. I moved as quickly as possible to minimize the length of
11


Plate 9a. Female bill shaking.
Plate 9b. Adult shading.


12
time each adult was off the nest. All nest site data were collected
in the winter months.
On Biven's Arm, observations were made from a rowboat anchored
50 feet from the nest sites. The same recording and optical equipment
was employed here. With the absence of avian predators, disturbance
of the nest site was less destructive here than on Sea Horse since the
nestlings were not subject to attack. This permitted daily visits and
determination of intervals between eggs, both at laying and hatching,
and growth rates of the young. Nest site parameters were measured at
the same time.
Durations of rapidly occurring behaviors were determined by
photographing activities at 18 frames per second and subsequently
counting the number of frames spanned by each. Data throughout are
presented as mean values (designated as x) with the sample size (desig
nated as "n") from which the mean was calculated. Ranges or standard
deviations (designated as "s") are included for most activities.
During pair formation, I selected individual males for observation
based on accessibility. These males were watched intensely through
formation of the pair or abandonment. Simultaneous data were collected
on associated females, including all motor patterns and the timing and
description of approaches to the male.
Attention was directed toward the details of copulatory behavior
and related activities during the four-year study. In addition to spot
observations on most of the pairs on Biven's Arm and the clearing on
Sea Horse, several were observed continuously over three or more days


minutes off eggs per pair hour
13
12
11
10
9
8
7
6
5
4
3
2
minutes off eggs
o temperature
all adults in <20% sunlight
o

0
0
0
A
(I
0 §
0
-j 1 1 1 I L
0500 0700 0900 1100 1300 1500 1700 1900
Hours
2100
Figure 8. Incubating adults number minutes off nest vs. time of day and C vs. time of day.
Data are from sunny days of May 1971.
34
33
32
31
30
29
28
27
26
25
24
23
22
cr>
Temperature (C)


99
it must provide information about the signaller that can be perceived
by and elicit a response from other individuals. When both participants
in a social encounter benefit from increased efficiency of the signals,
then any reduction in ambiguity is favored.
The displays of the White Ibis can be discussed within this
theoretical framework, including apparent origins of the behaviors
and the nature of the modifications that have taken place.
Snap Display (page 26). Individual elements of the Snap
display give indications of its origins. During nest building, males
gathering twigs extend their necks out and down, grasp a twig, and
shake it with both lateral bill movements and tugging. The scapular
feathers at this time are positioned variably, from compression to
full erection. These components are all found in the Snap display.
The duration of the neck extension during the Snap is longer
than the duration of bill thrusts; however, the speed of the extension
increases in the presence of a neighboring pair for the Snaps directed
toward it (and for these Snaps the scapular feathers are fully erected).
This suggests a second source of motivation for the Snap, that of in
hibited (and redirected) aggression.
Apparently both aggressive and nest building tendencies have
influenced the final expression of the Snap, reflecting the conflict
in motivations for the pair-forming male. The twig pulling component
is a common feature of the male's interactions with the female in
conflict situations. It is also seen in the Up-Down greeting display
and during pre-copulatory activities. Since the gathering of nest
material commences with the formation of the pair these twig pulling


Table 24. Comparison of the displays of the White Ibis and four groups of storks
(Ciconiidae). Apparently equivalent displays are listed in the same
horizontal row.
White Ibis
1
Openbilled Storks
2
Wood Storks
*3
Marabou Stork
+4
"Typical" Storks *
Forward Threat*
Forward Threat (FT)
FT
FT
FT
Stab-and-counterstab
Clattering Threat (CT)
* CT*
CT**

Alert Posture *
Anxiety Stretch (AS)*
AS*
AS**
AS*
Up-Down greeting
Up-Down greeting (UD)
UD
UD**
UD**
Cop. Bill Shake
Cop. Clattering (CC)
CC
CC
CC
Display Preen
--
Display Preen


Head Roll*
Head Rubbing (HR)
HR
HR
; HR
Snap**
Swaying Twig Grasp (STG) STG**
STG
Headshaking Crouch
--
Snap [unlike Ibises']
(S) s
S
--

Upright Display (U)
U
U
U


Balancing (B)
B


--
Aerial Threat
(AT) AT
AT


Gaping (G)
Erect Gape


Advertising Sway**
--
--
--


Flying Around
--


--


Mock Fighting
--


--
Threat Up-Down

--

--
Nest Covering Display
1 From Kahl (1972d); +2 From Kahl (1972b); h From Kahl (1966); $4 From Kahl (1972c).
* Slightly ritualized (= modified); ** Highly ritualized.


57
Table 15. Mean and standard deviation (s) of nest diameters
for clusters of synchronized nests and overall values.
Species *
N in
Cluster
X
Diameter
(inches)
s
Bay
6
9.3
0.82
12
9.2
0.87
15
11.1
1.03
9
12.1
1.05
11
9.2
1.08
13
9.1
1.11
7
10.6
1.13
10
10.0
1.15
6
9.7
1.21
12
8.6
1.29
5
9.2
1.30
9
10.2
1.30
7
9.4
1.40
12
10.9
1.51
9
9.8
1.56
17
9.4
1.58
8
9.9
1.73
10
9.4
1.84
9
10.4
2.07
Cedar
7
9.1
1.57
5
10.0
1.59
6
9.8
2.23
3
10.7
2.89
Oak
5
9.0
0.71
6
9.3
0.67
5
10.4
1.14
6
10.5
1.17
4
10.2
1.26
9
9.2
1.30
7
10.2
2.57
7
12.6
2.76
Palm
4
13.8
0.50
4
9.2
0.95
5
13.2
1.10
3
10.7
1.15
3
12.0
2.00
3
9.7
2.08
Yaupon
4
7.8
0.50
6
9.7
0.52
3
7.7
0.58
3
9.3
0.58
4
9.0
0.82
8
8.4
1.19
7
9.1
1.68
All trees in study
1051
10.0
1.89
*data arranged in order of increasing s for each species.


43
locality, lateness of the season, and day in the copulatory period
(1 and 2 vs. 3, 4, and 5). The most intense period of copulatory
activity occurred for Pair 3 on 6 April 1973 on Sea Horse (fourth
day of copulation). Following two copulations with other males by
the female at 1012 and 1026 hours, the pair copulated at 1033, 1048,
1100, 1145, 1210, 1308, and 1502.
Between copulations, the male of each pair gathers nest material
and the female constructs the nest. During the male's absence from the
nest site, neighboring males approach and attempt copulation with the
unattended female.
In 330 pair-hours of observation of 26 pairs during the copulation
phase, males attempted to mount females other than their mate 62 times.
Of 26 known females 16 were approached by 15 of 26 males under obser
vation and approximately seven unknown males. Of the 62 attempts only
12 were apparently successful (i.eterminated after lateral tail
pumping by the male and bill shaking by the female).
Only four of the 62 approaches met with even slight female
aggression. In each of these four instances, the female gave one slow
bill thrust in the direction of the male. None of these actually
struck and none was successful in discouraging the copulation attempt.
All 50 unsuccessful attempts were thwarted by another male, 46 by the
female's mate and four by another interloping male also trying to mount.
The female assumed a motionless, slightly crouched posture similar to
the normal pre-copulatory position 56 of the times she was approached.
Twice females greeted interlopers with the Up-Down display in the same
manner that they would their own mate. Males only approached females


143


the: study areas
Sea Horse Key
Sea Horse Key is a 154-acre island 2.5 miles southwest of
Cedar Key on Florida's Gulf Coast, and approximately 5.5 miles from
the Florida mainland. Figure 1 shows the position of Sea Horse and
the three other islands that collectively comprise the Cedar Keys
National Wildlife Refuge: Snake Key, North Key, and Deadman's Key.
Sea Horse Key is a remnant of a Pleistocene sand dune formed at a
time when the water level was greatly reduced (Wharton, 1958).
The waters around the island are diluted due to the fresh water
influx from the Suwanee River and the Wacassassa River, and support
a typical estuarine fauna and flora.
Sea Horse is surrounded by extensive tidal flats upon which
turtle grass (Thalassia testudimm) and manatee grass [Sy ring odium
filiforme) grow in abundance. In the winter and early spring these
grass flats are covered by only very sparse vegetation, and the
associated epifauna is reduced. By late May the grasses are extensive,
and crustaceans and polychaetes abound on and under the surface.
Along the northern shore where a channel has been dredged, the mud
banks and oyster beds exposed at low tide provide potential feeding
areas for the White Ibis.
These sites in the intertidal zone around the island provide
a limited amount of food for the ibises, especially late in the breed-
3


70
an hour, with the majority of the feedings occurring in the first 15
minutes. Table 19 gives values for feedings/15 min interval and seconds/
feeding for both Sea Horse and Biven's Arm. Crows and Black-crowned
Night Herons feed on very small young and the vigil by the parents
afford the young some protection. At 10 days of age, however, both
parents begin gathering food simultaneously leaving the young alone on
the nest. For the next 10 to 14 days the young stay in close proximity
to the nest but do visit neighboring sites, returning hurriedly to their
own nest when a parent returns with food. Following feeding the parent
leaves and the young continue their activities. It is during this period
that the behavior of the young is most easily observed--they are large
enough to see and yet too small to be excessively mobile.
All of the maintenance activities of the adults are performed by
the nestlings at this time; preening, leg and wing stretching, scratching,
feather ruffling, twig pulling, and even bill thrusting and allopreen-
ing between nestmates. When alone at the nest the young seek shade
during the afternoon hours. Strange adults arriving at the nest site
may or may not elicit a response from the young. Ten-day-old young show
both extremes from intensive begging to a crouched, motionless posture.
If the young do beg from a strange adult they are attacked,whereas, if
they lie still the adult is not aggressive.
Table 20 shows intervals between feedings for Sea Horse and Biven's
Arm, and the resulting differences in seconds of feeding/day at each site
are calculated in Table 21. Although the Sea Horse adults fed the nest
lings more times per 15 min interval (18.2 versus 14.8 for Biven's Arm)
and fed them longer at each feeding (4.8 versus 4.3 seconds for Biven's


Plate 6a. Basin bathing flock.
Plate 6b. Male and female stance at the nest.


7
(Casmerodius albus), Black-crowned Night Herons (Nycticorax nycticorax),
Yellow-crowned Night Herons (Nyatanassa violcea), Little Blue Herons
[Florida caerulea), Louisiana Herons (Hydranassa tricolor ruficollis),
and Snowy Egrets (Egretta thula) nest exclusively on the peninsula of
land extending north from the western end of the ridge (Gardner's Arm)
and in the black mangroves (Avicennia nitidia) along the island's north
shore.
There is little danger to nesting ibises on the island. The
only mammals present are the black rat (Rattus rattus) and the gray
squirrel (Scuirus carolinensis). Among the reptiles, only the locally
abundant cottonmouth moccasin (Agkistrodon piscivorus) is potentially
dangerous, and only to individuals on the ground. Of the avifauna, the
Osprey (Pandion haliaetus) and the Bald Eagle (Haliaeetus leucocephalus)
are large enough to potentially be of harm to the adults, but the eagle
is only a rare visitor and the Osprey, while locally abundant, inter
acts very little with the ibises.
The eggs and young of the ibises are in greater danger. Several
hundred Fish Crows (Corvus cssifragus) on the island are constantly
present in the rookery and are frequently seen flying with eggs in
their bills. At hatching, the threat from the crows declines but
predation by the Black-crowned Night Heron begins. This species
has been observed challenging adult White Ibises at their nest sites
for access to the young, rather than merely waiting for an exposed
nest as the Fish Crows do. The effects of the rats on eggs and small
young are unknown. If a nestling should fall to the ground it is
subject to predation by the cottonmouth.


114
vigilance and repeated insemination the male could not be assured of
parenthood, the system would not continue.
The nest attentiveness during nest building is striking, especially
on Biven's Arm, where the males do not gather while the female is off
just prior to egg laying. Males on Sea Horse occasionally leave the
nest unguarded at this time. The greater competition for sticks on
Biven's Arm may explain this difference in attentiveness since the
main benefit of the male's affinity for the nest at this time is
probably the prevention of theft. Later, with eggs and young in the
nest, the adults of Sea Horse are the more attentive ones (with the
extent of avian predation the probable reason for the difference).
The differing strategies employed by males in the collection of
nest material deserves mention. Some begin construction soon after
pair formation and others wait until as late as 48 hours prior to the
first egg. Those that wait seem to run the risk of loss of the first
egg and lack of materials, but perhaps the avoidance of direct
competition for materials and the increased number of piratable nests
later on enhance the desirability of this approach.
Incubation
The alternation of incubating adults at the nest during incu
bation allows both sexes to feed daily while allowing for constant
attendance at the nest site. The temperature of the eggs is maintained
by rapid descent by the relieving bird onto the nest.
The quantitative data from the 1971 season show incubation to be
a complex behavior. Length of time on the eggs per hour is an apparent


79
down and feed. If the new bird was aggressive and the established
bird turned away, the former became dominant. If the established bird
re-thrusted, then it became dominant and had first access to food. No
observed aggression went beyond these three exchanges and, once
established, no submitting bird ever showed subsequent aggression
toward the dominant. The latter merely had to raise its head or
administer a single bill thrust to elicit turning away. When the food
was plentiful, the more aggressive birds allowed the others to feed
in close proximity. As the food became scarce, however, all submitting
birds were driven away. Relationships of known young were stable
over several days and appeared positively correlated with size.
Crustaceans make up the bulk of the young ibises' diet on Sea
Horse. Fiddler Crabs [Uoa spp.) abound on the island and are a popular
food source. The ibises probe into the burrows, extract the crab,
bill it continously while adjusting its position, and swallow it with
the long axis of its body parallel to the bird's throat. Large male
fiddler crabs may grab the ibises' bill. When this occurs the bird
gives several billshakes until the crab relinquishes his hold. The crab
is then grasped by the arm at the proximal end and shaken until the arm
is autotomized. The arm is then discarded and the crab consumed. An
alternate response to pinching by a crab is complete disinterest sub
sequent to freeing the bill. Female fiddler crabs (without the large
claw) are selected before males by the young birds.
The young ibises selected fish before fiddler crabs when presented
with a choice at the feeding station, but were very inefficient at
capture. On several occasions fish intended for the young birds were


146
Wharton, C. 1958. The ecology of the cottonmouths Agkistrodon
piscvoras piscivorus Lacepede of Sea Horse Key, Florida.
Ph.D. dissertation, Gainesville, Florida, Univ. of Florida.


100
components cannot be considered displacement activities. The pair
forming male is motivated to copulate and build a nest simultaneously,
and both of these are in conflict with his aggression.
Baerends and Van Der Cingel (1962) discuss the origin of the
Snap display of the Common Heron (Ardea cinrea). The form of the
display closely resembles the Snap of the ibis. They suggest that the
display originated in redirected aggression, when the female approached
an unmated male. The ambivalent behavior was a result of conflicting
tendencies to attack, flee, and perhaps "settle down" on the nest.
The authors disagree with Meyerriecks* (1960) conclusion that it
arises from displacement twig pulling.
Whereas the male White Ibis Snaps only when alone, unmated, and
advertising, the Common Heron male Snaps in response to repeated female
approaches. It is apparently not used as an advertisement in this
species and, therefore, may not communicate the same degree of sexual
motivation as it does for the ibis. In any case, it does appear that
sexual motivation (in the form of twig pulling behavior) contributes
to the Snap display.
The Snap is a distinctive pattern, immediately identifiable to
a human observer, but its performance has many highly-variable components.
The wings are either held at the sides or extended at the carpal joint
(a movement indicating aggressive-escape motivation in gulls, according
to Tinbergen, 1959) and sometimes twigs are grasped, as discussed above.
The form of the neck extension itself distinguishes the display? however,
Head Bobbing (discussed below) and orientation of the extensions toward
neighboring pairs are frequent variations. Tinbergen (1959) discusses


141


Table 4.
Pair formation activities of 15 males and 25 females. These are composite
data for all years at both sites. Data collected throughout the day, from
as early as 21 March until as late as 10 June.
Activity
No./min.
Male
Range s
No.
Displays
No./min.
Female
Range s
No.
Displays
Snap*
6.5
0-25
4.4
1604

--


Head Roll
1.5
0-6
1.4
430
3.8
1-13
2.5
404
Display Preen
2.5
0-8
1.5
157
2.2
0-6
1.5
160
Preen
3.2
0-13
1.7
901
3.5
0-12
1.9
404
Feather Ruffle
0.96
0-4
0.7
62
1.1
0-4
0.75
40
Head Bob
3.7
0-8
2.4
214
_ _
_ _
_ _
* % with wing extensions 42.2
% with twig pulling 18.7
(n = 280 displays of 663)
(n = 94 displays of 503)


Plate 4a. Submissive posture.
Plate 4b. Snap display.


58
diameter is less than the overall value, illustrating the comparative
similarities of these parameters for the nest sites in the clusters.
Also, all of the nests of a cluster have a similar understory and
accessibility, and are composed of similar materials. Because all of
the nests are within a 25-foot radius, the pairs probably experience
similar wind velocities and predation pressures as well. No isolated
nests were observed on Sea Horse, and only four such nests were observed
on Biven's Arm.
The nest itself is constructed entirely of twigs up to three feet
in length and one inch in diameter, with the larger twigs forming the
basic framework and the smaller twigs the cup. The final addition to
the nest is a lining of leaves or Spanish moss. The leaves used are
from the immediate vicinity of the nest, further indicating the local
nature of nest material collection.
Egg Laying
The female lays the first egg on the fifth day after the beginning
of copulation. Incubation prior to completion of the clutch occurs
infrequently on both Sea Horse and Biven's Arm. The second egg is laid
two days later and the third egg (on Biven's Arm) laid two days after
the second (see Table 2). Table 16 gives clutch sizes for several years
on both Sea Horse and Biven's Arm. In every year the mean clutch size
on Sea Horse was <2.2 eggs per nest whereas at Biven's Arm it was
always > 2.8 early in the season. The mean clutch size late in the
season at Biven's Arm dropped to < 2.2, however. Table 16 also gives
data for clutch sizes for various populations of White Ibis from the


107
incubation) and the peaks at 1100 hours and 1700 hours may simply
reflect bursts of copulation prior to and following heat-induced in
activity.
The analysis of 63 intercopulatory intervals (Table 10) revealed
shorter intervals early in the copulation period. This probably
reflects the intensity of sexual motivation initially and, perhaps,
additional insurance for the male in counteracting early promiscuous
mating attempts.
Mating System
For every species, the mating system under which it operates is
a consequence of natural selection and, as such, will result in a
maximization of reproductive success for the individual. For most
avian species (> 90 per cent) this maximization is accomplished through
monogamy (Lack, 1968). Males and females, by restricting their activities
to one partner and the care of their offspring produce more young than
if they mated with more individuals and cared less for the young.
In order for another system to develop, such as polygamy or
promiscuity, one of the adults must be liberated from parental duties.
This is generally accomplished by a combination of precocial young
and richly abundant food supply. If the point is reached where a
female gains more of an advantage by pairing with an already paired
male than a single one (with perhaps poorer food supplies on his
territory for species that feed near the nest) the threshold of
polygyny is reached (Selander, 1972).


116
and until 10 days of age the nestlings are rarely left alone. De
composition of the organic matter adhering to the shell is a potential
problem also.
The narrow temperature range for the young is still maintained as
the parent shifts from sitting in an incubating posture to shading in
a crouched posture.
The high-pitched vocalization employed by the young when begging
is difficult for an observer to localize in the trees. Perhaps this
difficulty applies to predators as well.
When the young ibis is old enough to initiate feeding bouts by
hitting the adult, the pecks are oriented toward the distal 1/3 of the
bill. This is an area on many, though not all, of the adults that
retains a dark color, contrasting with the red of the facial skin and
proximal end of the bill. Perhaps this contrast facilitates locali
zation of the proper bill area by the young.
During the first 10 days, the continuation of adult alternation
at the nest is a compromise. It reduces the amount of food available
to the young, but it assures vigilance by a parent and temperature
control during the early life of the young, when homeothermy is probably
not yet efficient. At 10 days, when the adults discontinue their vigil,
the young are too large for any local predators and capable of tempera
ture control. The tenth day of the nestlings' lives is a critical one.
By this time they have gained mobility and can cross to nearby nests;
with that ability comes the possibility of an adult feeding someone
else's young. It is not surprising that individual recognition of
young by the adults develops by 10 days. Strange young discovered in


76
Table 22. Growth rates to 5 days for young from 6 nests
on Biven's Arm late in the 1973 season. Note
slower growth of 2nd young and lack of depression
in rate for nest with three young.
Position
Nest in Clutch 6 July 8 July
6
1
39.0
67.0
7
1
61.5
98.0
2
Egg
55.5
8
1
55.0
68.0
2
Egg
36.5
18
1
72.0
75.0
2
44.5
57.0
20
1
49.5
83.0
2
Egg
50.0
33
1
97.5
150.0
2
63.0
109.0
3
Egg
34.0
Date
11 July
A Wt (g)
A Wt./Day
228.0
189.0
37.8 g
215.0
153.5
30.7
99.0
43.5
14.5
172.0
117.0
23.4
62.0
25.5
8.5
180.0
108.0
21.6
107.0
62.5
12.5
207.0
157.5
31.5
123.0
73.0
24.3
252.0
154.5
30.9
220.0
157.0
31.4
89.0
55.0
11.0
Total
1296
24.0
1st young in 2 egg clutch 26.8 (n = 4).
2nd young in 2 egg clutch 15.0 (n = 4).


TABLE OF CONTENTS
Page
Acknowledgments ii
List of Tables v
List of Figures vii
Abstract viii
Introduction 1
The Study Areas 3
Sea Horse Key 3
Biven's Arm 8
Methods 11
Morphological Description and Major Preening Movements 14
Results 16
The Season 16
Numerical Increase on Sea Horse Key 16
Aggression 21
Pair Formation 26
Copulation 38
Nest Building 46
Egg Laying 58
Incubation 60
Behavior of Young 67
Comparisons Within the Order 82
Discussion 92
Comparison of the Study Areas.. 92
Habitat Comparison 93
Pre-Pair Formation Behavior 96
Pair Formation-Aggression 96
Analysis of Pair Formation Displays 97
Copulation 105
Mating System 107
i i i


Copulations/Pair Hours
0.8
0600 0700 0800 0900 0100 1100 1200 1300 1400 1500 1600 1700 1800
Hours
Figure 6. Copulation rate per pair hour for each hour of the day. Data are composite from all years
in both localities. Within parentheses are the total number of pair hours of observations
at each time.
-p*
PO


Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy
THE REPRODUCTIVE BEHAVIOR AND ECOLOGY OF THE
WHITE IBIS (EUDOCIMUS ALBUS)
By
Thomas J. Rudegeair, Jr.
March, 1975
Chairman: John H. Kaufmann
Major Department: Zoology
The behavior and ecology of the White Ibis, Eudoaimus albus, was
studied during the breeding seasons of 1971 through 1974 at two
locations in central Florida, an island in the Gulf of Mexico (Sea
Horse Key) and an inland lake (Biven's Arm). Quantitative data were
collected on many phases of the ibises* reproductive behavior, including;
arrival at the breeding grounds, aggression, pair formation, copulation,
nest building, incubation and care of the young.
The breeding season extends from early March until August, beginning
earlier at the Sea Horse rookery. Following initial numerical increases
at the rookeries, males select display sites and defend them aggressively.
They then advertise with the Snap Display, Head Rolling and Display
Preening. The females land nearby, face the male, and perform Head
Rolling and Display Preening, exposing the swollen guiar pouch to the
7
male. Mate selection is mutual, as the females approach the stationary
males. Partners greet at the nest with the Up-Dowr. display.
vm


47
Subsequent pairs form east of this point until they reach the clearing
in the center of the island (Area 2). Pairs then nest on the eastern
side of the island just beyond the clearing (Area 3), and not on the
edge of it, as might be expected. The birds then converge on the
clearing from east and west (Area 4). Finally, nest sites are selected
on the extreme eastern end of the hammock, in the isolated stand of
trees in the northeast section of the island, and in the trees border
ing the south beach (Area 5). In nesting seasons with fewer pairs
nesting, such as 1971 and 1974, Area 5 is not used. Trees in Area 5
are exposed to the formidable onshore winds. The trees in the principal
study area (Area 4) are used every year. The ibises do not nest in the
well-developed stands of black mangrove which occur along the northern
shore of the island around the border of Sea Horse Creek or the entire
Gardener's Arm area, the very sites selected by the herons and egrets.
This segregation of the ibis from the herons is not seen on Biven's Arm.
Here, the herons, egrets and the White Ibises all nest in close proximity
and interact.
When the pair has been formed and copulation has begun, the male
alone begins to gather nest material. I never observed a female gathering
nest material off the nest site or returning to the nest site with
material. The first trips of the male when nest building begins are
brief and often he returns without material. He gathers twigs first
in the immediate area of the nest and nearby unattended sites, and then
moves farther outward. On Sea Horse, although the thick vegetation
prevented continuous observation of males, most collections apparently
take place within 25 feet of the nest. These collecting trips are as


Table 20.
Feeding
intervals Sea Horse
vs. Biven
1s Arm and
Biven'
s Arm early vs.
late in
season
for young of two age groups.
Sea
Horse
Biven's Arm
Age of
Total
No.
Min.
Total
No.
Min.
Date
Young
Min.
Intervals
Interval
Range
Min.
Intervals
Interval
Range
1971
1-5
662
2
331
233-929




6-10
768
2
384
368-400
--

--

1972
1-5
2046
5
409.2
338-489
-


--
6-10
2207
5
441.4
350-510


--

Early 1973
1-5
761
2
385.5
341-420
824
4'
206
173-230
6-10

--

--
516
3
172
136-196
Late 1973
1-5
6-10
--



>1218
4
>304.5
--
Early 1974
1-5
610
3
203.3
168-240
6-10
--


--
853
5
170.6
118-225
Totals Early
1-5
3469
9
385.4
233-489
1434
7
204.9
168-240
6-10
2975
7
425.0
341-510
1369
8
171 .1
136-225
Overa11
6444
16
402.8
233-510
2803
15
186.7
136-240
Totals Late
1-5
_ _
>1218
4
>304.5



35
Mutual twig pulling with lateral bill shaking similar to that
performed at the end of the Up-Down display is performed in several
situations by the mated pair. It is seen following a nest disturbance
(for example, following a bill thrusting bout with a neighboring pair),
as a pre-copulatory activity, or without any apparent external stimulus
as the pair stands together at the nest site.
Male acceptance of the female when she approaches is not necessarily
an indication of pair formation. Once accepted, the female may be driven
off subsequently (29 of 60 observed cases) or she may depart without
provocation (31 of 60 observed cases). Table 7 gives the behavior of
the males for 80 approaches by the females including initial reaction
and behavior immediately prior to the female's departure. Prediction of
probable pair formation is difficult until the performance of the
first copulation. Of 15 pair formations observed, only two males
showed the Snap display after their initial copulation (i.e., 13 of 15
no longer performed pair formation displays).
The performance of the above behaviors results in a high
level of activity for pair-forming individuals, and this level is
reduced following the first copulation. One typical Biven's Arm pair
averaged 10.5 and 12.8 activities/min for the male and female, re-
specitvely, during the five minutes preceding the first copulation, and
3.7 and 5.7 activities/min immediately after.
Whereas the nest generally is constructed at the site of pair
formation, 20% (3 of 15) of the pairs abandoned this area after pairing.
Also, birds appeared in the study areas already paired, further in
dicating some mobility following formation. The stimuli for this move
ment are unknown.


N
Scale
Figure 7. Order of settlement of nesting areas, numbered chronologically. Area 1 settled
first. Entire nesting area is hardwood hammock. (Modified from Wharton, 1958.)
-P*
00


133


Table 16. Clutch size data for Sea Horse and Biven's Arm, and from inland Florida sites
(from the Florida State Museum egg collection).
Locality
Season
One
Egg
Size
Two
Egg
of Clutch
Three
Egg
Four
Egg
X
Sea Horse
1971
0
6
0
0
2.00
1972
4
42
14
0
2.17
1973
8
51
13
0
2.07
1974
7
56
7
0
2.00
Overa!1
19
155
34
0
2.07
Biven's Arm
Early 1973
0
2
20
0
2.91
Late 1973
3
24
9
0
2.16
Early 1974
0
3
13
0
2.81
Early overall
0
5
33
0
2.87
Late overall
3
24
9
0
2.16
Inland Florida sites*
1926
0
3
17
5
3.12
1928
0
2
9
0
2.82
1929
0
0
10
3
3.23
Overal1
0
5
36
8
3.08
*from museum


56
Table 14. The mean and standard deviation (s) of nest heights
for clusters of synchronized nest and overall values.
Species*
N in
Cluster
X
Height
(Feet)
s
Bay
5
8.7
0.27
10
5.6
1.40
10
6.8
1.43
13
10.9
1.50
11
10.1
1.58
17
6.1
1.66
12
9.5
1.82
6
16.3
1.86
6
18.5
1.97
7
12.3
2.06
15
14.8
2.24
12
9.8
2.45
9
15.0
2.65
12
13.2
2.67
7
13.4
2.70
9
12.4
3.20
8
11.0
3.25
9
11.4
3.50
9
16.4
3.84
Cedar
5
9.4
0.97
6
10.0
1.90
3
18.0
2.00
7
12.7
2.69
Oak
7
15.2
0.75
7
36.9
1.46
4
9.8
1.50
9
15.4
2.30
5
26.0
2.55
6
19.0
3.10
6
21.3
3.38
5
14.0
3.46
Palm
4
10.0
0.00
5
16.0
0.00
3
17.0
0.00
3
18.0
0.00
3
19.3
1.15
4
15.5
1.73
Yaupon
3
9.0
0.00
3
7.3
0.58
8
3.4
0.73
4
5.6
0.75
7
4.4
0.96
6
3.0
1.00
4
7.0
1.15
All trees in study
999
12.0
5.29
*data arranged in order of increasing s for each species


78
As the young approach independence (6-7 weeks), the adults
feed them only once/perch and they fly off, with the young pursuing.
The resulting pursuit flights usually involve one young and a parent,
but on Biven's Arm as many as three young have been observed following
a single adult. The flight may last up to several minutes, with the
adult circling and often landing in close proximity to the point of
departure. The young, even in flight, continue the high-pitched
vocalizations and generally, the first young to the adult is fed.
Once independent of the nest site the young on Sea Horse do not
merely wait in the treetops for the adults, but form flocks that walk
about on the island. Mid-morning flocks walk down the hill from the
dry, sandy clearing to the basin and feed along the exposed mud banks
at low tide, with individuals showing constant motion as they repeatedly
probe for invertebrates. Individuals in these feeding flocks exhibit
aggressive and submissive behavior such as Forward Threat postures,
bill thrusts, and turning away, all similar to the adult behaviors.
By placing food in pans at the base of the hill, it was possible to
observe these interactions at an intensified level due to the high
densities of young birds that developed.
Over several days the young ibises at Sea Horse established a
linear dominance hierarchy which determined access to food at the
feeding station I provided. When a new member arrived it was challenged
by those present. The Forward Threat was shown, followed by bill gaping,
bill thrusting (with a simultaneous harsh vocalization) and, in high
intensity interactions, grasping of the opponent's head and neck. The
new bird would either return the aggression or turn away with the head


Table 6. Temporal relationships of main
female.
Snap
Behavior
Relationship
No.
%
cfSnap
Following


cf Head
Roll
Following


9 Head
Roll
Following
43
27.2
^Snap
Followed by
--

^Head
Roll
Followed by
--

9Head Roll
Followed by
38
24.0
^Snap
Simultaneous with
--
--
tfHead
Roll
Simultaneous with


9 Head
Roll
Simultaneous with
24
15.3
pair formation activities between male and
Activity of Opposite Sex
Head Roll Preen Inactivity Other
No.
%
No.
/o
No.
%
No.
%
43
25.0
39
22.6
72
41.8
18
10.6
9
23.7
5
13.1
21
55.3
3
7.9
3.8
57
36.1
31
19.6
21
13.3
45
26.6
43
25.4
67
39.6
14
8.4
8
21.1
9
23.7
20
52.7
1
2.5
9
5.7
59
37.3
32
20.2
20
12.6
19
11.5
17
10.1
124
73.1
9
5.3
7
17.5
4
10.0
27
67.5
2
5.0
8
5.1
40
25.4
70
44.6
15
9.6
CO
CO


102
the bill is rolled, and rate of performance. It appears little
modified from the original behavior, probably performed as a displace
ment activity by females motivated to approach and avoid displaying
males. The female's orientation toward the male and the resultant
exposure of the red guiar pouch are consistent components. It appears
as though selection has favored exposure of the pouch via the Head Roll,
but has not produced the stereotypy of the behavior pattern commonly
observed in displays. Stereotypy achieves a reduction of ambiguity
that in this case may have been unnecessary. A Head Rolling individual
with a large pouch can only be an unmated female. The pouch rapidly
disappears after pair formation and, once paired, females remain at
the nest site most of the time.
Display Preen (page 30). This action does not reflect any
obvious internal motivation and may function to increase conspicuousness
of the displayer by adding to the general increase in activity level
seen during pair formation.
Up-Down Greeting (page 32). The transitional behavior shown
by the four males (page 34) clarifies the origin of the Up-Down
greeting. For the male at this time the female is both an intruder
and a potential mate. Through Head Rolling and maintaining a head-down
and crouched posture, she eventually releases non-aggressive behavior.
The bill thrust is transformed into a slow and exaggerated arching
motion. Since the male mounts with the neck extended, the upward
extension of the neck in the greeting display may have originated as
a sexual component, namely, as an intention movement for mounting.
In the early conflict stages the male neither mounted nor attacked;


52
Table 11. Division of labor for twig placement following male
return with nest material.
Locality
Year
9 Only*
9 Predominately
and 9
Equally
Sea Horse
1971
3
0
4
1972
32
40
8
1973
16
15
17
Biven's Arm
1973
12
3
15
Total
63
58
44
Percent.
38.2
35.2
26.6
males never placed twigs alone


LIST OF TABLES
Tables Page
1 Dates of first occurrences of nesting events
for both localities 17
2 Dates of key nesting events for 12 specific
nests on Biven's Arm (1973) 18
3 Mean ambient temperatures for the months
preceeding breeding 19
4 Pair formation activities of 15 males and 25 females .... 28
5 Rates of performance of male pair formation
activities (15 males total); comparison of
each year and both sites 31
6 Temporal relationships of main pair formation
activities between male and female 33
7 Initial behavior of displaying male when female
approaches and immediately prior to her departure 36
8 Pre-copulatory activities, both sexes 39
9 Post-copulatory activities male and female 41
10 Intercopul atory intervals 44
11 Division of labor for twig placement following
male return with nest material 52
12 Nest site data
13 Data on nesting trees 55
14 Mean and standard deviation (s) of nest heights
for cluster of synchronized nest and overall
values 56
15 Mean and standard deviation (s) of nest diameters
for clusters of synchronized nests and overall
values 57
16 Clutch size data for Sea Horse and Biven's Arm, and from
inland Florida sites (from the Florida State Museum egg
collection) 59
v


122
All copulations of the pair occur at the nest site at a mean rate of
once every 73 minutes for five days. During this time the males and
females in a nesting cluster engage in mutual promiscuity. Nearby
mated males approach a mated female when her mate is off gathering
nest material. Only 12 of 62 attempts were apparently successful,
however, due to the vigilance of males, who gather material in close
proximity to the nest site. Both males and females apparently benefit
from this mating system and the explanation presented in the Discussion
may be applicable to many other avian species, especially those nesting
colonially.
Only the male gathers nest material, and the female is the
primary builder. Males pirate material from adjacent unguarded nests.
Nests from the previous year are built upon or dissected.
Nesting on Sea Horse Key occurs in a regular pattern, beginning
on the western end of the hardwood hammock and moving eastward. Only
trees within the hammock are selected, and nests are constructed at
heights from 2.5 to 40 feet. Groups of five to 20 pairs begin copu
lation and nest building in synchrony. The nests within a cluster
show similarities for such parameters as height, diameter, species of
tree, and nature of the understory.
On Sea Horse Key the herons and egrets nest on another part of
the island, whereas on Biven's Arm the ibises, herons, and egrets nest
in close proximity.
The first egg is laid on the fifth day of copulation. The clutch
size on Sea Horse Key was less than 2.2 in each of the four seasons of
the study. On Biven's Arm it was greater than 2.8 early in the season.


66
While copulations between partners discontinue with the laying
of the first egg, promiscuous mating occurs in rare instances after
this time (observed three times in four years). Of the four cases
of bill thrusting by females toward approaching promiscuous males,
three took place during these late attempts. After the third day
of incubation no promiscuous mating attempts occur. Males still
approach nearby incubating females but, instead of copulating, they
pirate nest material. The female at this time greets interloping
males with the Up-Down display but does not leave the nest, as she
would if the approaching male were her partner.
The earliest case of shading behavior (dropping wings ventrally
while standing over eggs) was recorded on the afternoon of the fourth
day of incubation (at 1444 hours) with an ambient temperature of
34.0C, measured on the tower. The adult was fully exposed to the
sun. Shading was next seen on the 15th day (at 1423) by one adult,
again in direct sun. At 17 days all four adults observed showed
shading in 33C temperatures (first at 1446), even with no individual
fully exposed to sun. The posture is shown in Plate 9b.
Biven's Arm adults spend several minutes at a time as far as
10 feet from the nest when eggs or very small young are present. This
behavior is extremely rare on Sea Horse.
The incubation period is 20-21 days (see dates in Table 2).
Daily visits to the nest were possible only on Biven's Arm, and here
the young hatch two days apart. This asynchronous hatching indicates
that the first egg begins to develop before the clutch is complete.


Nest Building Ill
Incubation 114
Hatching and Early Life 115
Comparisons Within the Order 119
Summary 121
Plates 124
Literature Cited 144
Biographical Sketch 147
iv


27
18.7% of the displays; 94 of 503). The wings are cocked over the back
(occurred in 43.6% of the displays; 289 of 663) or held at the sides
during the neck extension. The male then assumes a normal roosting
posture. The entire display is performed in 1.1 seconds (n = 35;
s = 0.09). Table 4 gives frequencies of performance of the principal
pair formation activities, including the Snap. The male performs as
many as 25 Snaps/min at the height of display intensity, with a mean
of 6.5 (n = 1604; s = 4.4). He rotates his body constantly and
displays in all directions, never showing any prolonged orientation
toward any particular female in his area. The position of the scapular
feathers is variable during the performance of the Snap, from completely
compressed to fully erected.
A displaying male directs the neck extensions of the Snap down
ward at approximately a 45 angle unless there is another pair within
three feet. The male then directs all extensions toward the pair
when facing it. These Snaps are performed with the wings cocked and
the scapular feathers erected, and they are performed more rapidly
(0.67 sec; n = 4; s = 0.05).
Head Bobbing (new terminology). Head Bobbing, which appears
as a Snap minus a full neck extension, is also performed by displaying
males. It consists of a dipping motion of the head while the neck
remains retracted. It was performed at a rate of 3.7/min by the
three males for which it was quantified (n = 214; s = 2.4) as compared
to a snap rate of 5.9/ min for the same males. While Head Bobbing, the
males did not extend their wings or show associated twig pulling.


108
The ibis has hopelessly altricial young and, especially on
Sea Horse, must fly considerable distances to obtain food. Under
these conditions the assistance of both parents is essential for the
successful rearing of the young. Monogamy is expected and, whenever
a list has been compiled, the ibis has been called monogamous [e.g.,
Lack, 1968). However, the data show that following a monogamous pair
formation, males and females engage in a considerable amount of mutual
promiscuity.
The benefit of promiscuous mating for the male seems apparent.
He may be fortunate enough to father young he does not have to raise,
a favorable condition providing that the loss of sperm does not reduce
the likelihood of impregnating his own female. The adaptive significance
of this system for the female is less obvious. She invests a considerable
amount of time and energy selecting a mate based on qualities she per
ceives during the pair formation process, and then accepts sperm from
other males, presumably risking the loss of her mate's help. In the
absence of further data, several explanations for this female behavior
seem plausible: 1) Only nearby mated males approached females, suggest
ing that she may have been familiar with their individual characteristics
prior to the attempt. 2) Birds nesting in close proximity, with closely
synchronized cycles may represent extended families, introducing the
possibility of kin selection. Then females accepting nearby males
would be accepting gametes genetically similar to their mate's. How
ever, the mobility of some pairs following pair formation argues against
this possibility. A program of tagging over several seasons would
clarify this question. 3) Tables 14 and 15 show the reduced variability


97
guiar pouch and submissive postures of the female perhaps release
aggressive behavior in other females as well as sexual behavior in
males. This being true, there appears to be an added advantage to
directly facing the male when Head Rolling. If other females in the
area do not see the guiar pouch they may behave less aggressively,
allowing the properly-oriented female to remain closer to the male.
My data are insufficient to demonstrate that the female's orientation
affects other females in this way.
Analysis of Pair Formation Displays
Tinbergen (1952), Moynihan (1955), and Blest (1961) discuss the
modification (= ritualization) of behavior patterns and postures that
function as social signals. Displays originate, according to these
authors, as behaviors performed during conflict situations, for example,
during an aggressive encounter at a territorial boundary or at the
moment a pair-forming male sees a female approaching. At these times
the animal is motivated to perform antagonistic actions simultaneously;
in these examples, to attack and flee or to attack and mate. At such
times complete behavior patterns from neither source of motivation
are possible, and one of the following incomplete, ambiguous, or in
appropriate actions may occur: (1) Intention movement (after Daanje,
1950). These are the initial movements performed just prior to loco
motion. Intention movements for hopping in birds, for example, include
bending at the heel joint, lowering the breast, and drawing in the head
and neck. An animal in conflict may perform only these initial actions,
unable to locomote fully. (2) Redirected activities. An animal in


Table 25. Continued
White Ibis
Green Heron
1
$1
Snowy Egret
Circle Flight
Aerial Stretch
Tumble Flight
Jumping Over
^1 From Meyerriecks (1960).
2 From Blaker (1969).
Cattle Egret
$2
t
Great Blue Heron
1
Back Biting
Greeting Ceremony
00
I


113
while the bay trees held 67.1 per cent and only constituted 36.0 per
cent. The oakswerealso taller, and the mean height for a nest in
them was 18.0 feet compared with 11.6 for the bays. Perhaps this
is the reason for the comparative unpopularity of the oaks.
The diameter of the nest probably represents a compromise of
several factors. A small nest is less energetically expensive to
construct and less conspicuous. A large nest, however, provides
greater holding capacity for eggs and active young. The observed
size is an optimization of these parameters.
The degree of development of the understory would seem potentially
important if a young bird should fall from the nest. The clumsiness of
the nestlings and the jostling of a returning adult cause frequent
accidents. If there is sufficient vegetation for the young bird to
fall and climb upon, return to the nest is a possibility.
The nature of the sexual roles in nest construction is under
standable. The basic strategy of a mobile male gatherer and a stationary
female builder works efficiently, given the ibises' mating system. If
both sexes gathered material simultaneously, the nest would be pirated.
If the female collected while the male remained, it would be far more
difficult for the male to monitor her activities. The male stays
near the nest site to collect and returns frequently even without
material. Collecting nearby could be explained energetically, but
the expense of the male's constant returns without material argues
against energetics as the primary factor. This vigilance is success
ful in thwarting almost all promiscuous mating attempts and by so
doing, maintains the stability of the pair bond. If, through this


32
relationships between pair formation behaviors. The female Head
Roll was preceded by the male Snap 27.2% of the time, the male Head
Roll 3.8%, preening 36.1% and inactivity 19.6%. The Snap of the
male was preceded by the female Head Roll 25.0% of the time, female
preening 22.6%, and inactivity 41.8%. The male Head Roll was preceded
by the female Head Roll 23.7% of the time, female preening 13.1%,
and inactivity 55.3%.
Female Approach Attempts. Once a female has located a
male and has performed Head Rolling near him, she attempts to land next
to him on his display site. She flies with her neck extended downward
and her body contour feathers compressed, and crouches low upon land
ing. Initial approaches of this type are usually opposed by the male,
for he immediately administers bill thrusts to the head and neck of the
female. She flees, usually to her original perch, and the male immedi
ately begins to Snap again (an action that is discontinued as soon as
the female arrives). On Sea Horse as many as six females have been
observed surrounding a displaying male and approaching in this fashion.
The maximum number observed on Biven's Arm was two. The female returns
to the male after a mean duration of 5.7 minutes (n = 44), and after
several approaches begins to leave more reluctantly. Initially this
hesitancy increases the male's aggression and the female is forced to
flee.
Up-Down Greeting (after Kahl, 1972c, for the Openbilled
Storks, e.g.y Anastomus oscitans). Acceptance of the female by the
male is indicated by the Up-Down greeting display. As the female
approaches with her head down, the male raises his head and neck, gapes


72
Table
19. Extended..
Biven's Arm
Total
No.15 min.
Feedinqs No. sec. of
No.
Sec.
Feedings
Intervals
Interval Feeding
Feedings
Feeding
82
7
11.7
225.5
49
4.6
77
6
12.8
125.5
39
3.2
38
3
12.7
90.0
20
4.5
144
7
20.6
503.5
no
4.6
120
10
12.0
315.5
69
4.6
221
13
17.0
629.0
149
4.2
341
23
14.8
944.5
218
4.3


94
The comparatively early onset of breeding on Sea Horse may reflect
the importance of making an early choice of nest site on the island,
despite the possible cold weacher and reduced food availability.
The Biven's Arm male is restricted in his choice of a nest site
and both sexes are restricted in choosing a mate. The displaying male
is fortunate if two females approach. Mate procurement is more difficult.
The most obvious characteristic of Sea Horse is its isolation.
Being three miles off shore helps to limit terrestrial predators but
it necessitates lengthy, energy consuming trips to the mainland for
food. The mud and grass flats around the island are used very little
until the end of the breeding season. The late growth of the grasses
and the high salt content of the invertebrates found there may be the
bases for this lack of use. For whatever reason, however, the lengthy
trip to the mainland results in a slowing of the feeding process. The
maximum of two exchanges and feedings at the nest each day is probably
the key reason for the 2.1 clutch size for the Sea Horse population.
The proximity of Paynes Prairie to the Biven's Arm population
makes at least three trips per day possible early in the season. The
2.9 clutch size reflects this increase in food availability. Late
nesters, however, demonstrate reduced rates of feeding and lowered
clutch size (2.2). This may reflect a reduction in the availability
of invertebrates in mid-summer.
The White Ibis, then, demonstrates local variation in clutch
size, apparently as a function of food availability, a phenomenon well
documented by Lack (1968) for other species. The degree of difficulty
in finding food, however measured, is translated into a rate of egg
production.


145
Kahl, M. P. 1973. Comparative ethology of the Ciconiidae. Part 6.
The Blacknecked, Saddlebill, and Jabir Storks (genera Xenorhynohus,
Ephippiorhynchus, and Jabir). Condor 75: 17-27.
Lack, D. 1968. Ecological adaptations for breeding in birds. London,
Methuen and Co., Ltd.
Lancaster, D. A. 1970. Breeding behavior of the Cattle Egret in
Colombia. Living Bird 9: 167-194.
Meanley, B. 1955. A nesting study of the Little Blue Heron in
eastern Arkansas. Wilson Bull. 67: 84-99.
Meyerriecks, A. J. 1960. Comparative breeding behavior of four species
of North American herons. Pub!. Nuttall Ornith. Club 2: 1-158.
Moynihan, M. 1955. Remarks on the original sources of displays. Auk
72: 240-246.
Nesbitt, S. A., W. M. Hetrick, and L. E. Williams. 1975. Foods of the
White Ibis from seven collection sites in Florida. Proc. 28th
Conf. Southeastern Assoc, of Game and Fish Commissioners (in
press).
Palmer, R. S. (Ed.) 1962. Handbook of North American Birds, Volume 1.
New Haven, Yale Univ. Press.
Selander, R. K. 1972. Sexual selection and dimorphism in birds. Pp.
180-230 in Sexual Selection and the Descent of Man (B. Campbell,
Ed.). Chicago, Aldine.
Skead, C. T. 1951. A study of the Hadedah Ibis Hagedashia h.
hagedash. Ibis 93: 360-382.
Tinbergen, N. 1952. "Derived" activities; their causation, biological
significance, origin, and emancipation during evolution. Quart.
Rev. Biol. 27: 1-32.
Tinbergen, N. 1959. Comparative studies of the behavior of gulls
(Laridae): a progress report. Behaviour 15: 1-70.
Tinbergen, N., and R. A. Hinde. 1958. The comparative study of species-
specific behavior. Pp. 251-268 in Behavior and Evolution (A. Roe
and G. G. Simpson, Eds.). New Haven, Yale Univ. Press.
Trivers, R. L. 1972. Parental investment and sexual selection. Pp.
136-159 in Sexual Selection and the Descent of Man (B. Campbell,
Ed.). Chicago, Aldine.
Verner, J. 1965. Breeding biology of the Long-billed Marsh Wren.
Condor 67: 6-30.


THE REPRODUCTIVE BEHAVIOR AND ECOLOGY OF THE
WHITE IBIS (EUDOCIMUS ALBUS)
By
THOMAS J. RUDEGEAIR, JR.
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1975


DISCUSSION
Comparison of the Study Areas
Sea Horse Key and Biven's Arm provide habitats for the nesting
ibises that differ in many potentially significant details. Those to
be considered here include: 1) vegetation differences such as tree
species, tree height (and resultant number of potential nest sites),
amount of raw materials available for the nests, nature of the under
story, and the amount of shelter provided (from rain, wind, sun and
predators); 2) proximity to food sources; 3) types of predators; 5)
number of interspecific competitors.
Before any discussion of these differences and their apparent
effects, the basic similarity of behavior between the two populations
must be stressed. All of the behavior patterns of pair formation,
copulation, greeting, nest building and care of the young are essentially
identical at the two sites with respect to the components and duration
of each motor pattern. In cases where differences exist between the
two sites, the behaviors involved are quite variable within one popu
lation or even one pair (e.g.3 rates of performance of the Snap display,
as shown in Table 5). It is the rate of performance of the various
behaviors that differs most widely.
The basic similarity in motor patterns suggests genetic continuity
or, at most, only recent separation of the two populations. It seems
likely that there would be considerable mixing of two populations
92


63
Table 17. Minutes off the eggs (inattentiveness) for the block
of time 1200-1500 hrs. Included here are data for the
warm and sunny days only (1971).
Date
Day of
Incubation
Total min. of
Inattentiveness
1200-1500 hrs.
# of
Pairs
Min.
Pair
8 May
3
95
6
15.8
9 May
4
203
6
33.4
11 May
6
189
6
31.5
18 May
13
159
5
31.9
22 May
17
101
3
33.7
25 May
20
193
4
48.2


135


50
In the clearing at Sea Horse males began searching on the ground
for material on the third day of building. While known males collected
twigs close to the nest in all observable areas, individuals were seen
flying over the clearing with material in rare cases, indicating that
collecting some distance from the nest does occur.
Males begin gathering materials at dawn and some males work until
nightfall. Lack of audible wing flapping at night indicates that they
discontinue this activity after dark.
The male grasps twigs firmly with the bill and employs a lateral
or a push-pull motion in loosening them. Once freed in this manner the
twig is adjusted in the bill until the male has grasped it firmly in
the center. He then flies with it to the nest. Long or bulky twigs
are occasionally dropped or get caught in the trees. Males typically
show great perseverence in the pursuit of these problem twigs. One
male that dropped a twig while roosting on a limb near its juncture
to the trunk, reached out quickly with his leg and trapped the falling
twig against the side of the tree. He then reached down with the bill,
grasped the twig firmly, and returned with it to the nest.
When the male returns to the nest with material the female greets
him with a brief Up-Down display. The male may simply place the twig
down next to the female or, if it is small and easily managed, he may
extend his head and neck over the female's and place the twig in that
manner. In either case the female immediately seizes the twig and
begins lateral bill shaking while slowly moving her head forward (the
"tremble shove technique" of Meyerriecks, 1960). The male at this time
may either release the twig immediately or perform tremble shove move-


25
thrusting. Usually such a bout will take the form of a Stab-and-
counterstab ritual in which male A thrusts toward the head of male
B, while the latter is simultaneously retracting his neck (Plate 3b);
then the process is reversed. This usually results in little physical
contact and continues until one of the combatants turns away or be
gins fighting.
Fighting. When individuals are highly motivated, for example,
during the initial encounter between neighboring males or an unmated
male's first attack of an approaching female, the Stab-and-counterstab
is not demonstrated. At these times aggressive individuals strike
independently at the opponent, frequently biting the head and neck.
It is only during this type of bout that injuries are a likely
possibility. Bill thrusts are performed in 0.3 seconds (n = 33;
s = 0.06).
In violent bill-thrusting bouts at the nest site, the resident
male attempts to move into a position above the intruder and direct
his thrusts downward. This is accomplished by climbing upward or by
actually mounting the intruder. This latter behavior occurs only if
the intruder is a female.
Aerial Aggression. Whereas several of the herons exhibit
aggressive, extended pursuit flights during this early period
(Meyerriecks, 1960), the male White Ibis never travels more than
10 to 15 feet to repulse an intruder and, once the intruder takes
flight, the resident male returns to his display site. Aerial combat in
this species is rare, seen only as a result of apparent accidents in the
timing of displacement attempts. On three occasions males 10 to 15 feet


Plate la. Female ibis, with guiar pouch well developed
Plate lb. Male ibis, with guiar pouch poorly developed


127


84
(Kahl, 1972e), in comparison with the White Ibis. Display descriptions
are taken from Kahl (1966, 1972b, 1972c, 1972d). Table 25 gives
similar data for the Green Heron, Snowy Egret, Cattle Egret, and the
Great Blue and Great White Herons. Descriptions are taken from
Meyerriecks (1960) who considers the Great Blue and Great White
Heron's as color phases of the species Ardea herodias, Blaker (1968),
and Lancaster (1970). These species were selected due to the range
of sizes they represent. Furthermore, the Snowy and Cattle Egrets
demonstrate breeding requirements similar to the ibises'.
A comparison of the two tables shows that the displays of the
White Ibis most closely resemble those of the storks. Each major
behavior pattern in the ibises' repertoire has an apparent counterpart
in at least one of the stork tribes. According to Kahl 's analysis,
the storks vary widely in the degree of ritualization of each behavior
pattern. The term ritualization, as applied in this study, refers to
the process of modification (through stereotypy, simplification, ex
aggeration, repetition, etc.) of a communicative signal (= display)
from original behaviors performed during times of conflicting motivation
(see the discussion of Pair Formation). The Marabou Stork performs the
most elaborate (and modified) displays and the Openbilled and Wood
Storks (Mycteriini) the least elaborate. The Openbills also have the
least number of displays. Most of the heron displays differ in appear
ance from those of the White Ibis.
The alert posture looks very similar in all species compared.
Only the Marabou Stork deviates, with the addition of wing spreading
to the posture. Kahl refers to the alert posture as the Anxiety


46
females on Biven's Arm leave the nest site on day three as well but,
unlike the Sea Horse females, they may feed two or more times by the
laying of their first egg.
Early in the copulation period vocalizations are audible at
night but wing flapping is much less evident than during pair formation.
Spot checks indicated that most pairs spend the night together at the
nest site, with approximately 15% of the pairs represented by only one
member after dark.
Allopreening was observed 10 times in the four years of data
collection, all 10 occurring during the copulation period. Performance
of preening was divided evenly between males and females (five each).
Allopreening occurred both before and after copulation and during
periods of nest material collection by the male, apparently independent
of copulatory behavior. Participating pairs ranged from newly formed
to four days old. In all cases the dorsal surfaces (the back and neck)
were the target areas.
Very few copulations occur after the first egg appears on the
fifth day of copulation.
Nest Building
Nesting begins on different parts of Sea Horse over several weeks.
Pair formation is rarely performed by a single couple at a given location
but, rather, by clusters of five to 20 pairs all synchronized within
24 hours of each other and clumped together spatially.
The island is not settled randomly. The earliest pairs each
year nest on the western side of the island, (Area 1, Figure 7).


109
of nest height, diameter, and tree species within the clusters. If
all the approaching males are from the same cluster, then they have
selected nest sites similar to the mate of the female. Since all
females were approached only by males in the same area and, con
sequently, from a nest site with many similar characteristics, the
disadvantage of accepting another male may be reduced if male nest
site preference is the criterion upon which the female bases her
selection of a mate (see the discussion of nest building). The
simplicity of the pair formation process for the ibis suggests that
the female may be selecting more on the basis of the quality of the
area the male has chosen. The Snap display may serve to inform the
female of a male's availability, followed by her close scrutiny of
the site he favors. Gilliard (1956) first discussed the idea of
transferral of female selection from the male to some inanimate object,
in his example, the bower of bowerbirds. Transferral to the nest site
has been suggested for the Long-billed Marsh Wren as well (Verner, 1965).
Perhaps, more accurately, the female may be choosing on the basis of
the male's observed ability to select a favorable area (or build a
suitable structure) rather than on the basis of his morphology or dis
plays. Site selection may be correlated with abilities during nest
building as well. 4) The female who accepts an interloping male and
is impregnated by him produces progeny who may inherit his stealth,
aggressiveness, and ability to form a pair (since all males involved
are paired). If these offspring in turn produce more young as a result,
then acceptance of the male is favored. A female who merely accepts
any male who approaches is receiving sperm from either an aggressive,


34
his bill, and instead of thrusting downward, slowly arches his neck
through 90 to a vertically downward position, simultaneously giving
a soft honking vocalization. He may lower his bill next to the
female's, or he may extend the arch over her, resulting in crossed
necks. The female, still holding her head low, may remain motionless
or join in by also arching the neck from the horizontal to the vertical
with the male. Often brief twig pulling with lateral bill movements
occurs as the bills reach the vertical position, especially in later
greetings by the pair. The pitch of the vocalizations given during
this ceremony are variable from the low "honk" of the male to the
high-pitched scream of the female.
Four males demonstrated the transitional behavior involved in the
change from rejection to acceptance of the female attempting to pair.
Due to the female's crouched posture, the blows to her head are
directed downward and the bill thrusts are administered with typically
rapid pumping motions. For these four males, the females left less
readily after several approaches and each had to attack more vigorously.
The first indication of their acceptance of the female was a redirecting
of the bill thrust adjacent to the female's head rather than at it.
At the end of these thrusts each male showed twig shaking with lateral
bill movements. Initially these redirected attacks were interspersed
with actual blows to the female's head. The next step in the acceptance
process was a reduction in the speed of the redirected thrust as the
males began arching their necks over that of the female. Not all males
demonstrated this transition from pure aggression to greeting. In 11
of 15 cases the male simply switched from one to the other in temporal
sequence.


17 Minutes off the eggs (inattentiveness) for the
block of time 1200-1500 hrs 63
18 Rate of performance of activities during incubation
period 65
19 Feeding rates of young for Sea Horse and Biven's Arm .... 71
20 Feeding intervals Sea Horse vs. Biven's Arm and
Biven's Arm early vs. late in season for young of
two age groups 73
21 Composite calculation of seconds of feeding/day at
Sea Horse and Biven's Arm, based on data from
Tables 18 and 19 74
22 Growth rates to 5 days for young from 6 nests on
Biven's Arm late in the 1973 season 76
23 Survival rates of young to 10 days 83
24 Comparison of the displays of the White Ibis and
four groups of storks (Ciconiidae) 85
25 Comparison of the displays of the White Ibis and
four heron species (Ardeidae) 86
VI


15
feathers are extended during this motion. With the wing held loosely
away from the side of the body, the ibis preens along its outer edge
with a smooth stroke directed posteriorly. With the wings similarly
positioned the bill is brought over the shoulder and pointed vertically
downward to preen the under surface of the wing. The back is preened by
merely turning the head posteriorly and erecting the back feathers.
The abdominal region and ventral tail feathers are preened by bending
the head down and reaching between the legs with the bill.
The bill is rubbed against the oil gland at the base of the tail
and subsequently the bill and the side of the head are rubbed along the
back feathers. This action often grades into rolling of the head from
side to side while keeping it in contact with the back. During preening
activity the head is often shaken from side to side with the bill
pointing vertically downward. This head shaking motion is typically
followed by preening of the ventral surface of the body. Feather
ruffling is performed following a preening bout or, less frequently,
from a motionless roosting posture. The wings are held away from the
sides and alternately shaken up and down, with simultaneous erection
of the back and neck feathers. Finally, the head and neck are shaken
rapidly.
The ibis scratches directly over the wing with the longest toe.
The head is lowered and cocked to bring the area to be attended into
position.
Two types of stretching are common. The wing and leg of the same
side are extended downward and posteriorly, or, both wings are cocked
over the back while the head and neck are extended out and downward.


101
the adaptive significance of possessing several different displays
that communicate different levels of motivation, and he briefly
mentions the variations sometimes observed within a given display.
The Snap of the ibis appears to be more effective as a signal with
these variations than without. The neck extension itself attracts
females (and repels males) initially. The frequencies of associated
Head Bobbing, twig pulling, and wing extensions may then serve to
inform the female of the male's particular motivation levels. This
is the only advertisement he has, and it appears to be rich in infor
mation. The Head Bobbing seems correlated with low motivation (recall
the abandonment of display sites by two of the three Head-Bobbing
males) and the wing extension seems correlated with high levels of
aggression. The rate of performance is itself a variable parameter
that may reflect underlying levels of motivation.
Head Bobbing (page 27). Head Bobbing appears to be a low
intensity Snap display. Perhaps the bobbing motion indicates the
intention of neck extension while revealing the lack of sufficient
motivation to perform it completely. Head Bobbing males did not
extend their wings or pull at twigs, further indicating lack of
intensity.
Head Rolling (page 29). This pair formation activity is
clearly derived from the more extensive head rubbing motions employed
during preening. The rolling motion is common to both, but the rate
of performance is greater in pair-forming individuals and initial oil
extraction from the uropygial gland is absent. The display has quite
variable duration, angle of the bill while rolling, angle through which


90
Unmated male Openbilled Storks also perform an Advertising Sway
in which they bend over with the bill low and pointed back 25 degrees
beyond the vertical, and shift their weight from one foot to the other
while swaying the bill slowly from side to side (Kahl, 1972c). It is
highly ritaulized, according to Kahl, and shows an "obvious relation
ship" to Swaying Twig Grasping. He reports that it is performed only
by unmated males who are apparently trying to attract females. The
Snap of the White Ibis has the same function.
Among the herons Head Rubbing has been reported for the Cattle
Egret only (Blaker, 1969). All of the herons show a Stretch display
in which the head is brought into contact with the back feathers, but
it is apparently derived from an intention movement for flight rather
than from preening (Daanje, 1950). Also, the heron Stretch does not
function in pair formation but, rather, functions in nest relief,
synchronizing nest construction, and as a pre-copulatory gesture by
the female (Meyerriecks, 1960).
The Snap display of the Green Heron and the Snowy Egret is
essentially identical to that of the White Ibis. It is performed only
by the male during pair formation, and there is considerable variation
in its performance (including Head Bobbing). Snowies sometimes perform
the Soap off the nest site but the Green Heron never does. Meyerriecks
(1960) believes the Snap originated in twig pulling movements for the
herons, but Baerends and Van Der Cingel (1962) disagree (see discussion
of diaplays).
Both the storks and herons demonstrate displays not seen in the
ibis. Among the storks, the Openbills show the fewest number of


118
harsh vocalizing and turning away indistinguishable from the behavior
of my artificially fed flocks (p. 78). The density of food particles
in the feeding situation I created is different from the usual wild
condition. On the mud flats the crabs are scattered and conflicts
are rare. Since these flocks of young apparently consist of the same
individuals each day, there is a potential for the development of a
linear dominance hierarchy of the type seen under the artificial con
ditions, which could potentially be useful if food sources become
scarce and competition increases.
Another possible application of this capacity for individual
recognition and establishment of dominance is during the adult feedings
in the treetops. Here young are observed supplanting others and
obtaining conspicuous roosts. If visibility increases as a function
of roost site then the efficiency of parent-young location would increase.
Nest mates competing for food from the same parent may also determine
access by a limited hierarchy of two or three individuals.
The loose flocks of the feeding ibises provide many eyes and
ears for potential predators in the open habitat of the marsh and grass
flats. Local concentrations of invertebrates are more efficiently
discovered by a mobile, probing group of birds than by individuals.
Unlike the slow, deliberate stalking of the herons, the ibis feeds in
constant motion: probing, withdrawing and relocating the bill.
The tidal effects on feeding intensity are obvious; the prey is
only accessible up to approximately four inches of water. The flocks
of young also show a distinct recession of feeding activities in the
afternoon, even at low tide, suggesting a temperature effect (their
dark plumage may facilitate overheating).


of establishing a linear dominance hierarchy that apparently determines
access to limited food sources. Their feeding activities through the
day are correlated with tidal and temperature fluctuations.
x


60
egg collection of the Florida State Museum. For all of these inland
populations the mean clutch size was > 2.8.
Between the laying of each egg, the female feeds while the male
tends the nest, and it is at this time that the alternation of adults
at the nest begins. This phenomenon occurs at both Sea Horse and
Biven's Arm, but the intervals between exchanges at the nest are quite
different (see Table 20).
Incubation
Consistent incubation begins with the completion of the clutch.
Figure 8 shows the relationship between the number of minutes off the
nest (inattentiveness) and the time of day. On the same graph is a
plot of the mean ambient temperature per hour interval, using only
the days of relatively uniform temperature. Both lines assume an
approximate bellshaped curve with maxima at 1500 hours. The smooth
shape of the curve showing the number of minutes off the nest per hour
is disrupted somewhat by the depressed value for the hour 1200 to 1300.
As the graph indicates, all six pairs were shaded over more than 80% of
their bodies at this time.
Figure 9 shows the mean number of minutes off the nest per hour
for each day of observations. Days on which rain occurred and days on
which observations were made only during the hours when temperatures
were highest are indicated.
Table 17 gives values for the number of minutes off the nest
per pair for the block of time 1200 to 1500 hours for each sunny day
in an effort to determine the change in attentiveness as the 21-day
incubation period progresses. Time off the nest is low on day three of


68
the parent. Until day seven all feeding is initiated by the adult that
returns with a crop full of food, positions its bill vertically, and
lightly grasps the bill of the young. This stimulates the young to
raise its head upward, sliding the bill up to the mouth of the adult.
At this point the adult gapes widely and the nestling's head literally
disappears into the parent's mouth. There follows a series of head
jerks as the food is regurgitated directly into the nestling's mouth
(Plate 10b). The process of transfer takes from three to 10 seconds
after the nestling's head is in position. Once fed initially the young
begin issuing a begging call--a rapidly oscillating scream of one to two
seconds in duration repeated as often as every two seconds. In the
first days the bill is held horizontally and not oriented in any par
ticular direction. The head bobs up and down as the nestling calls
with the wings extended and fluttered simultaneously. At about seven
days the young has grown large enough so that it can reach the bill of
the adult when begging (Plate 10a). At this time the bill is no longer
randomly oriented, but is aimed at the distal 1/3 of the adult's bill.
The head bobbing now brings the tip of the young's bill into repeated
contact with the adult's, stimulating the adult to move the bill to
the vertically downward position and gape while the bill of the nestling
slides up and into the adult's mouth. Feeding at seven days still
takes between three and 10 seconds, with head jerking more pronounced
than it is for newly hatched young.
The first young hatched is generally larger than his nestmate(s)
and can reach higher during this active begging. The adult attempts to
feed both by moving its bill away from the larger young once it has been


93
separated by only 60 miles in a species that migrates from as far as
Central America or Northern South America. It is possible, of course,
that the young return to the site of their birth to nest two years
later. The final answer to the question of genetic isolation lies in
an extensive tagging program.
Assuming gentic continuity, any differences observed in the two
populations must arise as a function of local conditions acting on
flexible behavior.
Habitat Comparison
The Sea Horse rookery is vast and diverse. Thousands of ibises
congregate and begin selection of sites and mates among trees with
potential sites of highly variable heights, exposure (to sun, wind, rain
and predators), proximity to each other, and understory. On Biven's Arm
in a typical year perhaps a hundred ibises must compete with several
other species for nest sites of much less apparent variability.
There are several consequences of these differences in the
vegetation and the resultant number and quality of the nest sites. Each
member of the Sea Horse population is presented with considerable choice.
The male must decide on a nest site. The timing of his cycle will
determine which areas of the island are available. Once there, the
microhabitat is a matter of individual selection and retention. The
female has tens or even hundreds of displaying males from which to choose
and the male is typically approached by several females. Mate selectivity
is possible and, for the female, the type of site chosen by the male
from the array of possibilities must be considered an important criterion.


80
thrown too close to the water's edge and escaped. In such a situation
the young were totally inept at pursuing the fish. Some young birds
even carried sand covered fish to the water, and submerged them. In
these cases the fish quickly escaped. The analysis of Nesbitt et at.
(1974) reveals that fish constitute only 1.0% of the ibises' diet.
Feeding activities are most pronounced at low tide during the
morning and evening hours. Figure 10 graphs the relationship between
the number of ibises feeding in the basin and the time of day, with
the tide extremes indicated. While low morning and evening tides
result in intense feeding, low tides in the afternoon fail to stimu
late much activity. Observations were made through a complete tidal
cycle but, as the graph shows, by 23 July most of the young had left
the island and few were seen even at low tide in the morning.
The young drink at any standing fresh water source, but were
never seen drinking salt water. They dip the head and neck, keeping
the bill horizontal until it enters the water. They then raise the
head, elevate the bill about 10 degrees above the horizontal, and open
and close the bill four to 10 times while swallowing. This action may
be repeated up to 20 times in a drinking episode.
Seven-week-old young showed a curious behavior on the white sand
of the clearing at Sea Horse. In a flock of 20 young birds, 10 turned
their backs to the sun, spread their wings, and laid down on the hot
sand while simultaneously guiar fluttering. After 13 minutes in this
position, the birds rose and walked into the shade, continuing to guiar
flutter. Tin's spreadwing posture was seen only once and never in the
shade.


2
Arm) provide contrasting habitats for nesting White Ibises. Con
sequently, they provide an opportunity to learn of the behavior of
a common but little-studied species and to simultaneously compare
that behavior in two distinct ecological settings.
The discussion emphasizes the adaptive significance of the basic
reproductive strategies employed and the environmental causes for the
differences observed in the two populations. The mating system of the
ibis (monogamy with subsequent mutual promiscuity) is discussed at
length and its possible merits reviewed. Also presented is a brief
summary of the ethological theory of the origin and evolution of
displays, and a consideration of the ibises' pair formation displays
in that context.


112
order in which nesting areas were occupied was constant (see Figure
7). The western end of the main ridge was settled first. At this
point the trees of Gardner's Arm (the site of heron nesting) probably
afford maximum protection from northerly winds. The same species of
trees are present on the western end of the main ridge, as in the rest
of the hammock, although the habitat appears less dense. Perhaps the
reason for initial nesting here may be simply that the birds become
familiar with this area while they are roosting during the two weeks
prior to the commencement of breeding.
Once settlement here has begun, new nesters simply spread
eastward into suitable sites. The clearing and its human population
interrupts the flow and the eastern end beyond it is settled first.
The data on nest site parameters (Tables 12 and 13) show the
variability of the nest sites selected on Sea Horse and the comparative
similarity on Biven's Arm. This variation on Sea Horse gives the male
a wide range of choices. On Sea Horse the nests are higher because
the trees are taller. There seems to be no advantage to high nests.
In the absence of ground predators low nests are in little danger.
As the height increases the effect of the wind increases, and the
distance which the young may fall and must subsequently climb to
return increases. The chief predators are in the air and presumably
the higher the nest, the more conspicuous it is to these predators.
The limited data from 20 nests support this hypothesis: a greater
number of young survived to ten days in the lower nests (Table 23).
Table 13 reveals that oak trees held only 12.2 per cent of the nests
while constituting 25.9 per cent of the trees in the rookery,


Plate 10a.
Young begging orientation.
Plate 10b.
Young receiving food.


123
This difference is apparently the result of the greater distance the
adults on Sea Horse Key must fly to obtain food (greater than three
miles, compared to 1.5 miles for Biven's Arm adults) and the associated
reduction in feeding rates of the young on the island.
Incubation begins with the completion of the clutch and adults
alternate at the nest site. Attentiveness to the nest varies with
environmental conditions. The incubation period is 21 days.
The young are fed by direct regurgitation and are attended by
one of the parents at all times until 10 days old, while the other
parent gathers food (primarily crustaceans and insects). Prior to
10 days of age, the young are susceptible to predation from Fish Crows
and Black-crowned Night Herons. At four weeks the young can fly
short distances. At five weeks they no longer return to the nest site,
but are fed in the tree tops. Independence is achieved in seven weeks.
The young ibises are capable of establishing linear dominance hierarchies
in all-young feeding flocks. These flocks are active primarily at low
tide in the morning and evening hours.
The courtship activities of the White Ibis most closely resemble
those of the Openbilled and Wood Storks. Heron courtship is characterized
by a greater number of activities, most of which have no apparent
homologue in the White Ibis or the storks.


67
Behavior of Young
The young escape the egg by pecking a hole at one end of the egg
(usually the blunt end). Adults were never observed assisting in the
process, although when the young has emerged the adult removes the
shell from the nest and discards it with a lateral bill shake. This
same bill movement is seen throughout the cycle when debris falls
into the nest itself. The behavior of the adults changes very little
for the first day of the nestling's life; they rise, reach into the
nest as if turning eggs, shake twigs, preen and sit precisely as before
hatching.
In the first few days of life, the young ibises on Sea Horse are
susceptible to predation by Black-crowned Night Herons. On two occasions
the herons were observed flying with young in their mouths, and their
presence in the rookery is common. Adult ibises defend against
intrusion by the Black-crowns with threat displays and actual bill
thrusting if the heron attempts to land at the nest. Fish Crows also
are capable of taking one-day old birds and their presence also alerts
the adults.
One rather unusual predator destroyed my study site in 1971. An
immature Bald Eagle landed among five nests, resulting in immediate
flight by the adults. Of the seven young present (10 days old) two
were killed outright, two fell to the ground and were lost, one was
displaced from the nest five feet, and the others were unharmed.
The newborn ibis is covered with a soft black down, is blind,
and for the first day is barely capable of raising its head. By the
second day, however, the nestlings can raise up and accept food from


13
of the five-day copulatory period. For each copulation the time,
duration, pre- and post-copulatory events, and associated behaviors
were recorded. From these data a detailed description of the White
Ibises' behavior during the copulation period was possible, including
copulation rates, intercopulatory intervals, and the extent of
promiscuity.
During the 1971 season six nests on Sea Horse were observed on
10 of the 21 days of the incubation period, and all activities of the
adults were recorded. From this record, taken as early as 1/2 hour
before dawn until darkness, a complete description of incubation
behavior could be generated. The data reveal when each bird stood
over the eggs, what he or she did while up, and when each one resumed
incubation. The rate and dynamics of the exchanges of the adults at
the nest site were also recorded.
Unless otherwise stated, the descriptions of the behavior of
the White Ibis are a result of data from both study areas, and general
izations apply to both. Details are presented for behaviors that differ
between the populations.


95
The ibises of Biven's Arm run the risk of complete destruction
of the nest if a raccoon should gain access to the rookery. It seems
unlikely that fine adjustments in nest position or construction would
reduce the threat. Nest vigilance also seems pointless against such
an aggressive predator. On Sea Horse the problem is different. There
is no threat from the ground, but crows and Night Herons are effective
predators on eggs and young from the air. Crows approach only exposed
eggs, however, and the Night Heron, while more aggressive, will retreat
before an aggressive ibis. Subtle nest positioning that would reduce
conspicuousness from the air and an increase in nest vigilance by the
adult ibises would seem beneficial under these conditions. This type
of predation, therefore, further increases the importance of male nest
site selection and the female's consideration of it.
Differences in nest attentiveness at the two sites may also be
attributable to the differing intensities of predation by visually
orienting avian predators. During incubation and the early days of
the care of the young, the Biven's Arm parents spend portions of time
roosting several feet from the nest, leaving its contents in view. Such
a deliberate exposure is extremely rare on Sea Horse. Even when not
incubating or brooding, the adult stands directly over the nest itself.
The highly synchronous nature of the nesting on Sea Horse is
perhaps related to predation as well. Being one of several nests in
an area, each providing the same potential food source for a predator,
may reduce the possibility of any individual nest being selected. While
most of the ibises were synchronous on Biven's Arm, isolated pairs were
observed in both 1973 and 1975. Such isolation was never seen on Sea
Horse, in four years of observations.


88
Stretch display, emphasizing the social signalling function of this
response to disturbance. The neck extension and head cocking serve
the individual more directly, however, by increasing its field of
vision. I choose to stress this apparent function in the naming of
the posture.
All species demonstrate the Forward Threat as well, although in
this display the ibis differs from all others by extending the neck.
The more intense Full Forward display of the Green Heron does include
extension of the neck, however.
Ritualized fighting is performed by the White Ibis, Cattle Egret,
and all but the "typical" storks (Ciconiini). Kahl gives the name
Forward Clattering Threat to this activity for the storks, whereas I
prefer the more descriptive Stab-and-counterstab, used by Blaker (1968)
in his description of ritualized fighting for Cattle Egrets. This
display in the Marabou Stork is least similar to the ibises' while
the Openbills and Wood Storks show the greatest similarity. Pictures
of the Forward Clattering Threat of the Wood Stork (Kahl, 1972b, Plate
3) look very much like the ibises' posture (Plate 3a). Stab- and counter
stab is not described by Meyerriecks for any of the herons he studied
(1960).
The Up-Down greeting display is remarkably similar between the
storks and the White Ibis. All storks perform it, and the description
and pictures of it for the Openbills fit the ibises' pattern precisely,
including the honking vocalization of Anastomus osoitans, the neck
extension of the male over the female, and the frequent twig pulling
at the end of the display. The Wood Storks add a side-to-side motion


44
Table 10. Intercopulatory intervals. The 63 values are grouped
as to locality, time of season and stage of the
copulation cycle.
Intercopulatory
(x min)
Interval
Range n
Locality
Sea Horse 75.5
Biven's Arm 59.7
Time of Season
Early 80.0
Late 58.3
Overall 73.2
Stage of Copulation
1-2 days 65.9
3-4-5 days 77.9
11-191 54
22-124 9
11-186 43
21-191 20
63
21-140 32
11-191 31


137


different activities. Among the herons, the Cattle Egret shares the
most displays in common with the ibis, and has the fewest extras.
The Snowy Egret, Green Heron and Great Blue (= Great White) Heron
perform several unique patterns.


Figure 5. Approach routes of returning flocks as indicated by arrows and principal roosting
areas.(modified from Wharton, 1958).
no
CO


29
Two of these three males abandoned their display sites within two
hours after I began observing them.
Only unpaired males perform the Snap and Head Bobbing. All
other pair formation activities by both sexes are apparently intact or
slightly modified preening movements, with only the frequencies of
performance altered.
Head Rolling (new terminology). Head Rolling is performed
by both sexes during pair formation and is the dominant activity of
unpaired females searching for a mate. The bird orients its bill
horizontally and perpendicular to the body. The side of the head is
laid against the back feathers. From this position the head is rolled,
raising the bill above the horizontal. The bill may be carried a
full 180, through the vertical, to the other side, or as little as
30. A normal roosting posture can be assumed after one roll, or the
head may be rolled back and forth for several seconds. A single roll
takes 1.1 seconds to perform (n = 21, s = 0.31). Plate 5a shows an
example of bill orientation when it passes through the vertical position.
The male performs this activity in temporal sequence with the Snap at
a rate of 1.5/min (n = 430, s = 1.4). The female, in response to the
Snap displays of the male, will land within 15 feet of him, face him
directly, and perform the Head Roll at a rate of 3.8/min (n = 404;
s = 2.5).
This behavior appears quite similar to the rolling movements
performed during head rubbing, the preening activity described earlier.
There is little rubbing during the Head Roll, however, and there is
no temporal association between rolling and the oil extraction from
uropygiai gland, as there is during head rubbing.


no
opportunistic interloper or, if he is thwarted, by a vigilant arid efficient
mate. If her partner cannot effectively prevent her promiscuity this
may constitute a shortcoming in the male that would be passed on to
their sons, consequently reducing their fitness. 5) The female may
also benefit from the insurance of multiple partners. All of the
females in this study copulated predominantly with their mates, and
he still seems to be the likely father of the young. In the event of
sterility, however, the promiscuous female could still produce a
viable clutch. The possibility of sperm competition should be
mentioned here as well.
In the absence of data on the relationship of the timing of in
semination to ovulation and the efficacy of sperm transfer and use in
promiscuous interactions, conclusions must be speculative. The extent
of male persistence at interrupting a partner's promiscuity, even though
this slows nest building,suggests that completed promiscuous copulations
are effective. This being the case, these data suggest an interesting
and complex selection process involving perhaps one or more of the
above considerations. The simultaneous selection for monogamous pair
bonding followed by mutual promiscuity is the apparent result.
I believe these considerations suggest a possible reevaluation of
the extent of monogamy among birds. The number of avian species that
are presently considered monogamous perhaps is inflated due to a lack
of extensive observation and quantification of copulations particularly
among species in which pairs nest in close proximity. Many studies of
breeding behavior emphasize pair formation activities, aggressive displays,
territoriality, nest building, etc., but deal with actual copulation only


Plate 8a. Male descended -
ill positions.
Plate 8b. Female cradling male, male tail depressed.


Table 8. Pre-copulatory activities, both sexes. The larger sample size for the
female is a result of closer observation of her at this time.
o*Pre-Copulatory Behavior 9Pre-Copulatory Behavior
Year
Locality
Twig Pulling
Inactive
Preen
Twig Pulling
Inactive
Preen
1971
Sea Horse
2
0
0
2
1
0
1972
Sea Horse
0
0
1
1
2
1
1973
Sea Horse
5
0
0
5
11
0
1973
Biven's Arm
8
1
0
8
9
0
Total
15
1
1
16
23
1
Per Cent
88.2
5.9
5.9
40.0
57.5
2.5
CO


75
Arm), the Biven's Arm adults could provide approximately 27/ more
feeding time per day (224 versus 175 seconds for Sea Horse) by virtue
of the shorter interval between visits (3.1 versus 6.7 hours for Sea
Horse). Table 20 further shows the increase in the interval for
Biven's Arm late in the season (up to 5.1 hours).
These tables, divided into data for young birds 1 to 5 days and 6
to 10 days old, also reveal changes in rates of feeding with age. Both
Biven's Arm and Sea Horse adults fed the older young more often and at
the same time, more quickly. The data for each year, however, reveal
that these changes did not occur in all years.
Changes in the intervals between feeding visits with the age of
the young were opposite at the two sites. At Sea Horse in both 1971 and
1972 the interval increased with age, while at Biven's Arm it decreased.
Comparisons between male and female feedings reveal little
difference. Sea Horse males and females fed young at the rate of 17.4
and 17.6/15 min respectively and Biven's Arm males and females at a
rate of 15.9 and 14.2/15 min respectively. Table 22 gives data on the
growth rates for the young from six nests on Biven's Arm late in the
1973 season. The rate of growth was highest for the single nestling
on nest six (37.8 g/day). On the nests with two offspring, the first
born grew faster (26.8 versus 15.0 g/day for the second-born). However,
growth is more rapid after the first few days and the data for the
second-born are primarily from these early days. On the only three egg
nest measured, there was no observable depression of the growth rate of
the first and second nestlings (30.9 and 31.4 g/day).


103
the greeting display was the resultant compromise. Twig pulling again
appears in a display that involves a conflict of mating and aggression
motivation.
In comparison with the herons and egrets on Biven's Arm, the most
conspicuous aspect of the White Ibises' pair formation is its simplicity.
The Snap of the male performs the necessary advertisement. The female's
Head Roll and associated guiar pouch provide the necessary sexual
identification. The herons employ several vocalizations and a variety
of aerial and stationary displays during pair formation. The number
of closely related sympatric heron species may account for the difference.
Historically, individual herons of similar but gentically incompatible
sympatric populations had to identify conspecifics. Those for whom
faulty communication resulted in fruitless interspecific pairing,
failed to make a contribution to the next generation. Selection favored
the development of unambiguous signals. The elaboration of several
displays for each species, identifying and isolating individuals in
it from the others, is the apparent result. The White Ibis has only
one close relative, the Scarlet Ibis (Eudocimus ruber) whose breeding
range is confined to South America. Without the disadvantages of
possible ambiguity, the simple signal system seems more desirable.
It attracts less attention from potential predators, conserves energy,
and involves a minimum of genetic information to both perform and
interpret the motor patterns. This simple sysem, then, probably
represents the primitive pattern in the order (see the discussion of
Comparisons Within the Order).


9
select sites and have similar nesting requirements. An estimated
maximum of nesting White Ibis pairs on Biven's Arm was 200 in 1972.
Nearby Lake Alice on the University of Florida campus provided
nesting sites for the ibises until the degredation of the area in the
early 1960s, at which time the birds discontinued nesting. Simultane
ously, the previously unused Biven's Arm area became the site of an
active rookery. In recent years, however, the lake has attracted land
developers. As a result, the buffer zone between the birds and the
human population has decreased and human use of the lake has increased.
In 1974 an estimated 30 pairs of ibises fledged young from the Biven's
Arm rookery.
Whereas the number of ibises in the area is low, the pairs nest
in close proximity (nearest neighbor 1.8 feet) and, with the addition
of nesting Little Blue Herons, Louisiana Herons, Snowy Egrets, and
Cattle Egrets (Avdeola ibis), there is considerable competition for
space and materials. Despite this density of nesting birds, Biven's
Arm has at least one advantage. The vast feeding grounds on Paynes
Prairie reduce the time and energy that must be spent flying to gather
food for the young.
The only predators observed on the nesting grounds were two
mammalian species. Raccoons (Pvocyon Lotov) and domestic cats (Felis
domestica) were both observed near the rookery and are presumably
responsible for the large scale nest abandonments and destruction that
occur periodically. The stunted nature of the vegetation prevents escape
from such predation. There is apparently very little avian predation
of the ibises' eggs or young on Biven's Arm. Although Fish Crows are


49
brief as they are close to the nest, the mean duration of male absence
from the nest when returning with a twig being 2.8 min (n = 127). Even
when unsuccessful at obtaining any material, collecting males return to
the nest every 4.2 min (n = 42).
At the height of nest building in an area any nest left unguarded
is pirated, usually within 15 min if active males are present. Males
visit abandoned sites repeatedly (as often as 17 times in 30 min) and
whole nests can be disassembled in an afternoon. Throughout nest
building activities, which continue well into incubation, the pair
alternates absences from the nest. Males usually do not steal material
from tended nests, although on two occasions on Sea Horse males from
nearby nests have been observed pulling twigs from beneath an incubating
female.
Males collecting nest material usually interact little with each
other. Aggression occurs when two males simultaneously select the same
twig. This was only observed on Sea Horse when males were on the ground
and covering large areas in search of twigs. Interactions were brief.
One male administered a bill thrust to the head of the other and the
latter turned away and walked off. The first male to the twig was the
aggressor in the few cases observed (n = 4). A single rasping vocali
zation accompanied the bill thrust in all four encounters. Males on the
ground at Biven's Arm were almost impossible to observe, but they did
show considerable movement and wing flapping, suggesting that, in the
limited area in which they were collecting material, competition for
twigs on the ground during nest building and aggression of the type
described above may have been more pronounced than on Sea Horse.


Figure 1. Sea Horse Key and surrounding area. Snake, North and Sea Horse Keys comprise
the Cedar Keys wilderness study area (from Wharton, 1958).


Table 25. Comparison of the displays of the White Ibis and four heron species (Ardeidae).
Apparently equivalent displays are listed in the same horizontal row.
White Ibis
Forward Threat
Stab-Counterstab
Alert Posture
Up-Down Greeting
Cop. Bill Shake
Display Preen
Head Roll
Snap
il
Green Heron
ti
Snowy Egret
*2
Cattle Egret
+1
Great Blue Heron
Forward Threat (FT)
FT
FT
FT

--
Stab-Counterstab

Alert Posture (AP)
AP
AP
AP
--

Wing
Touch
?

Head
Rubbing

Snap (S)
S
--
S
Crest Raising (CR)
CR
CR
CR
Stretch (ST)
ST
ST
ST
Upright (UPR)
UPR

UPR
Flap Flight (FIF)
Aggressive Upr. (AU)
FI F
AU
Full Forward (FF)


FF
Advertising Calls (AC)
AC
AC
AC
Bittern Stance (BS)
BS
--

Bill Snapping
--
--
--


36
Table 7. Initial behavior of displaying male when female
approaches and immediately prior to her departure.
Initial cT Behavior
n
& Behavior Prior
to ? Departure
n
(-)* Bill thrust
20
(-) Bill thrust
18
(+) Inactivity
2
(+) Greeting
50
(-) Bill thrust
23
(+) Inactivity
20
(-) Other
7
(+) Inactivity
10
(-) Bill thrust
6
(+) Inactivity
2
(+) Twig pulling
2
(-) Totals
20
(-)
18 (90.0%)
(+)
2 (10.0%)
(+) Totals
60
(-)
29 (48.3%)
(+)
31 (51.7%)
+ denotes acceptance
- denotes rejection


INTRODUCTION
The behavior of the members of the avian order Ciconiiformes
has been extensively studied in recent years. Andrew Meyerriecks
(1960), for example, has closely examined the breeding behavior of
four species of herons (Ardeidae) and M. P. Kahl (1966, 1972a, 1972b,
1972c, 1972d, 1973) has studied the reproductive displays of the storks
(Ciconiidae). A third family in the order has been largely ignored,
however. The behavior of the ibises (Threskiornithidae; subfamily,
Threskiornithinae), represented worldwide by some 26 species, has
been studied by only a few workers. The published reports contain
only brief qualitative descriptions of breeding activities; e.g.,
ffrench and Haverschmidt (1970) on the Scarlet Ibis (Eudcoimus ruber),
Skead (1951) on the Hadedah Ibis (Hagedashia hagedash), Beebe (1914)
on the White Ibis (Eudocimus albus) in captivity, and Meyerriecks
(in Palmer, 1962) on the White Ibis.
This study reveals the reproductive behavior of the White Ibis
in quantitative detail including arrival at the breeding area, aggression
and pair formation, details of the mating system, copulation, nesting
strategies, incubation, and raising of the young. Also examined are
the effects of such ecological parameters as varying predation pressure,
food availability, and nest site availability.
Two sites close to the University of Florida campus, an isolated
island in the Gulf of Mexico (Sea Horse Key) and an inland lake (Biven's
1


21
Whereas single individuals fly to and from the island, flocks
of four to 20 birds are most common. During the evening returns early
in the season flocks of 200 individuals are not uncommon. The ibises
often fly in a Vee formation with individuals equally spaced, but this
structure is quite flexible and changes in a few seconds to an undulating
straight line either parallel or perpendicular to the direction of flight.
Figure 4 illustrates the changing profile of a returning flock sketched
from movie film. The ibises glide frequently and often a wave of
gliding will pass down a column. As a line of birds moves it encounters
local air currents and updrafts, creating undulations like a ribbon in
the wind.
All flocks arriving early in the season fly to the western end
of the island and roost there. Bare mangrove branches in close proximity
to other roosting birds are the most popular sites. Figure 5 shows the
island with its principal approach routes and roosting areas employed
during this period. At dawn the birds fly either directly to the main
land from the western end of the island or east across the island and
off its eastern end. The first indication of the onset of breeding
occurs when several hundred of these individuals fail to leave at dawn.
Aggression
The behavior of individuals that return for the commencement of
breeding activities is noticeably altered. Many do not show character
istic headlong flight but, rather, fly with their bills pointed downward
(examining the vegetation?). Loose flocks land periodically, roost
briefly, and depart. At this time there is virtually no site attach-


69
fed one or two times. If the size difference is great, however, the
larger young often climbs over the smaller and succeeds in obtaining
several consecutive feedings. In these cases the differences between
young are augmented further. At times when the adult is attempting to
feed the smallest young, both nestlings often reach for the adult's
mouth simultaneously. This results in the abortion of the feeding
attempt via the assumption of an erect posture by the adult; the nestlings
then revert to the begging vocalization.
Returning adults do not all begin feeding the young immediately.
A period of inactivity may precede the onset. If the young are large
enough to reach the horizontal bill of the adult, the bill is often
placed on the back and out of the nestlings' reach. This behavior also
occurs when the adult has finished feeding the young but they continue
to beg.
Up until approximately 10 days of age, the young locomote poorly
and remain on the nest site, although they do climb onto immediately
adjacent limbs. On two occasions five and seven-day-old young were
accidentally displaced from their own nest by the parent and crawled
into a neighboring one. In both cases they were fed along with the
resident nestlings but subsequently returned to their own nests.
Several young of ages 10-20 days were in a neighboring nest when the
adult returned and these were immediately attacked and driven off.
Young ibises at age 10 days move freely from nest to nest in an area
but are fed only by their own parents. Individual recognition of young
by parents apparently develops at the time the nestlings gain mobility.
Up until the age of 10 days parents continue to alternate at the
nest site. The young are fed by the returning parent intermittently for


51
ments with the female. The twig pulling at the end of the greeting
display is now functional. The latter activity occurs most often with
larger twigs in the initial stages of construction.
Table 11 shows quantitatively the division of labor for actual
construction of the nest. The data reveal that while the female is the
principal builder the male makes a considerable contribution, assisting
the female in placement of material in 27% of the cases observed (n =
165). Release of the twig by the male is followed either by his
preening or departure for more material. Males that characteristically
help the female very little still demonstrate twig pulling with her
prior to copulation. Following copulation these males revert to merely
dropping twigs on the nest and departing. Males continue supplying
material through at least the first half of the incubation period.
When relieved at the nest site by the female during incubation,the male
collects for a time before departing for the feeding grounds. Males
have been observed returning up to 15 times with material before
leaving to feed. The female always departs immediately for the feeding
grounds when relieved.
Males show considerable variation in the timing of their gathering
efforts. Some begin collecting twigs immediately after pair formation
and, with the females, build a considerable structure by the third day
of copulation. Others collect very little until the third or fourth
day of copulation and then work intensively for 24 to 48 hours, complet
ing a structure sufficient to hold the first egg on day five. This
variation in the timing of nest building occurs on both Sea Horse and
Biven's Arm.


ACKNOWLEDGMENTS
I would like to express my gratitude to my advisory committee,
Jack Kaufmann, Jim Lloyd and David Johnston, who guided me during the
collection of data and the writing of this dissertation. Thomas Emmel
and Thomas Patton, who reviewed my work have also been of particular
assistance.
My work on Sea Horse Key was greatly aided by Edward Collingsworth,
who granted me permission to work there, and Frank Maturo, Lee Belcher,
and A. D. Folks who provided transportation and made living on the
island comfortable.
Study of the Biven's Arm rookery was made possible through the
kindness of Jim Wing, who donated the use of his boats.
I must also include thanks to my friends for their moral support,
especially Donna Gillis and all who assisted me with data collecting.
My wife, Frannie, deserves special mention. She helped me in the
field, in the preparation of rough drafts, and in solving all resultant
problems. She was my inspiration.
Support for my research was provided by the Department of Zoology
of the University of Florida, an estuarine studies grant from the
Division of Biological Sciences and a grant from the Frank M. Chapman
Memorial Fund of the American Museum of Natural History.
I


Table 21. Composite calculation of seconds of feeding/day at Sea Horse and Biven's Arm,
based on data from Tables 18 and 19.
Mean No. Sec.*
Feedings*
No.15 min. Feedings^
Seconds Feeding
Locality
Feeding
15 minutes
Day
Day
Sea Horse
4.8
18.2
2
=
175
Biven's Arm
4.3
14.8
3.5
=
223
'fc
From Table 19.
^From intervals between feedings; the number of feedings possible through the day
is approximated (also, on Sea Horse, two feedings/day is the observed maximum).


PLATES


Table 18. Rate of performance of activities during incubation period. Included are
rates overall, on rainy days, and on days on which data were collected
during hot hours only.
Pair
Hours
(Pr. Hrs.)
Mo. Times
off the
eggs
Na Min. up
Preen
Twig Pull
Feather
Ruffle
Head Shake
Tail Flick
Stretch
Scratch
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Pr. Hr.
Overal 1
365
3.5
6.9
2.6
1.9
0.20
0.12
0.26
0.24
0.56
Rainy Days
90
1.9
1.9
1.3
0.83
0.36
0.20
0.11
0.07
0.27
Sun Days *
70
4.3
13.9
3.3
2.7
0.13
0.13
0.22
0.29
0.71
*days when data were collected only during warmer hours (1100-1600).
CT>
cn


22
Figure 4. Changing profile of a linear ibis flock, broken into two
sections. Time scale appears on left (n ~ 100). Sketched
from super 8 mm movie film. Picture taken from Sea
Horse of flock returning from the mainland.


24
ment, overt regression is minimal, and mobility is high. Passive
displacement, the departure of one bird when another lands nearby, is
the most noticeable form of interaction.
By noon of the first day some males select sites from which they
will display and on which the nest will be constructed. As attachment
to this single site increases, aggression toward intruders becomes
more pronounced. Initially males are aggressive toward any individual
that approaches within six to 10 feet. Aggressive behavior takes one
of the following forms.
Forward Threat (after Meyerriecks, 1960, for the Green Heron,
Butorides viresaens, and Kahl, 1966, for the Marabou Stork, Leptoptilos
crumeniferus). Active displacement is accomplished by walking or
flying toward an intruder with the body horizontal and the neck
extended in the Forward Threat posture (Plate 2a). In most instances
this approach results in flight, with the intruder turning his back
to the attacker, compressing the body plumage and lowering the head
(Plate 4a), and walking or flying off. This is less likely to occur
if the other individual is also a resident male with some site
affinity.
Stab-and-counterstab (after Blaker, 1969, for the Cattle Egret).
If the intruder does not retreat, the attacker recoils his neck,
raises the bill above the horizontal, and begins thrusting the
head outward, striking with the gaped, pointed bill. These aggressive
males consistently show erection of the scapular feathers. If the
intruder at this point is equally tenacious he faces the attacker,
assumes a similar recoiled posture (Plate 3a) and also begins bill


Table 2.
Dates of key nesting
Arm (1973).
events for
12 specific
nests on
Biven's
First Day
Last Observed
Egg
Young
Nest
of Pair
Copulation
1st
2nd
3rd
1 St
2nd
3rd
1
26 Apr
30 Apr
1 May
3 May
5 May
22 May
23 May
7
2
26 Apr
30 Apr
1 May
3 May
5 May
22 May
23 May
?
4
26 Apr
?
30 Apr
2 May
4 May
20 May
21 May
22 May
6
11 Jun
14 Jun
15 Jun
18 Jun

6 Jul
7

7
11 Jun
?
15 Jun
17 Jun
--
5 Jul
7 Jul

8
11 Jun
?
15 Jun
17 Jun
19 Jun
5 Jul
8 Jul
?
9
11 Jun
15 Jun
16 Jun
18 Jun
?
N. H
N. H.
N. H.
13
11 Jun
7
7
?
?
7
?
7
18
11 Jun
?
?
15 Jun
7
7
?
7
20
11 Jun
14 Jun
15 Jun
17 Jun
7
6 Jul
?
?
30
11 Jun
7
16 Jun
18 Jun
?
N. H.
N. H.
N. H.
10
11 Jun
15 Jun
?
?
7
?
?
7
--not laid
N. H. not hatched
? date unknown


26
apart flew toward each other simultaneously in apparent mutual dis
placement attempts. The result was a mid-air collision in all three
cases with single bill thrusts exchanged, followed by landing and
turning away by one of the combatants.
Female Aggression. Females demonstrate the same postures,
movements, and feather erection as males, but less readily. Lone
females confine their attacks to other females exclusively and
administer bill thrusts to males only when mated and on the nest
site. Even under these conditions intersexual female aggression is
rare in the absence of her mate. Intrasexual female aggression is
most common during pair formation when females, attracted by the same
male, land close to each other.
Pair Formation
Once a male has succeeded in establishing himself on a display
site, he begins the performance of pair formation activities. All
displaying is conducted at this site and, when displaying, he is mobile
only in the pursuit of an intruder. The following are the principal
activities of pair-forming individuals.
Snap Display (after Meyerriecks, 1960, for the Green Heron;
Kahl, 1966, uses this terminology for a different behavior pattern of
the Marabou Stork). The unmated male White Ibis performs one con
spicuous advertising display, the Snap. The male, from a stationary
position, crouches and simultaneously extends the head and neck out and
downward (Plate 4b). At the apex of the display he may close the
slightly gaped mandibles over a twig and shake it briefly (occurred in


Figure 2. Sea Horse Key, showing vegetation and sites of rookeries (modified from
Wharton, 1958).


5
ing season, but the bulk of the food for the young must be obtained
from the brackish marshes along the mainland coast. The round trip
is a minimum of eight miles and feeding flocks have been observed
as far inland as Otter Creek, 20 miles east of Cedar Key.
Nesbitt et al. (1974) report stomach contents of 46 White
Ibises nesting near salt water in Florida (30 from Sea Horse).
Crayfish (Pvocambarus sp.) were found in 44.1% (by volume) of the
stomachs, crabs (primarily Uoa spp.) in 23.4%, and insects (eight
orders) in 24.3%. Vertebrates were less prevalent; fish were found
in 1.0%, reptiles (primarily snakes) in 3.0%, and no amphibians.
Sea Horse Key slopes upward from the north and south shores to
a central ridge running in an east-west direction. Wharton (1958)
describes the flora of the island and the micro-habitat differences
of the northern and southern slopes. His work is the source for the
scientific names of the trees mentioned in this study. The ibises
nest on the slopes in the trees of the oak and bay-dominated hard
wood hammock that thrives there (Figure 2). These 60 acres of
potential nest sites have supported as many as 200,000 White Ibises
(in 1972, according to the staff of the Chassahowitzka Wildlife
Refuge) since the island was first used for nesting in 1960. Nests
are constructed in six species of trees at heights ranging from 2.5
to 40 feet. The forest floor is open in most areas and its wealth
of fallen twigs readily accessible to nest-building birds.
There was virtually no interspecific competition for nest sites
or materials observed on Sea Horse. The ibises nest only on the central
ridge whereas the herons and egrets, including the Great Egrets


55
Table 13. Data on nesting trees. Number and per cent of nests
in each species and number and per cent of each species
in hammock on Sea Horse.
Trees in x
Nesting Nest
Nests in t Areas % Height
Species* n Total n Total (feet)
Sea Horse:
Tmala littoralis (Bay) 706
Quercus virginiana (Oaks) 128
Quercus lauri folia
Sabina silioioola (Cedar) 44
Sabal palmetto (Palm) 42
Ilex vomitoria (Yaupon) 41
"vines" 91
Biven's Arm:
Sambucus canadensis (elder) 61
Acer rubrum (Red Maple) 10
67.1
154
36.0
11.6
12.2
111
25.9
18.0
4.2
45
10.5
11.26
4.0
89
20.8
14.19
3.9
29
6.8
5.93
8.6
--


85.9
14.1
*species names from Wharton (1958)


Plate 2a.
Forward threat.
Plate 2b. Biven's Arm rookery.


RESULTS
The Season
The breeding season of the White Ibis in central Florida
extends from as early as mid-March until the end of August, by which
time all of the young birds are fully independent of the parents.
Table 1 shows the dates for first occurrence of several key events
for each year of the study at both of the study areas, and Table 2
pinpoints precise dates for 12 nests on Biven's Arm in 1973. Table 3
shows the mean ambient temperatures at the Apalachicola weather station
for January through April in the years the study was conducted, and
the date of the first observed copulation for each year.
Numerical Increase on Sea Horse Key
The early increase in White Ibis numbers in March is apparent
on the island from late afternoon until nightfall. Most birds leave
the island at dawn in the direction of the mainland and its extensive
marshlands. At 1500 hours flocks begin returning to the island and
continue to do so until nightfall. The number of birds that returns
at this time increases steadily for at least two weeks prior to any
actual breeding activity. Figure 3 shows the pattern of numerical
increase for a day during this period prior to pair formation (14 March
1974).
16


17
Table 1. Dates of first occurrences of nesting events
for both localities.
Sea Horse Biven's Arm
1971
1972
1973
1974
1973
1974
First signs of
numerical increase
3 Mar
10 Mar
19 Mar
12 Mar
First copulation
17 Apr
20 Mar
31 Mar
28 Mar
27 Apr

First egg

24 Mar
4 Apr
--
30 Apr
1 Apr*
First young

15 Apr

23 Apr
21 May

First young alone
at nest
_ _
26 Apr
..
4 May
31 May
*abandoned
--no data


8
Biyen's Arm
Biven's Arm is a 200-acre lake in Gainesville with drainage
onto Paynes Prairie to the southeast. Surrounding the lake is a zone
of small red maples [Acer rubrum) and elders (Sambucus canadensis)
approximately 30 feet in width. On the southwest side of the lake,
this zone takes the form of a series of small floating islands, most
of which are separated from the shore by a narrow water or mud barrier
(depending upon rainfall). Numerous fallen trees, however, usually
render these islands accessible to mammalian predators. Immediately
behind this zone of small trees, on the shore itself, are towering
oak trees (Quercus sp.). While often roosting in these trees, the
ibises nest exclusively in the small maples and elders near the water
(Plate 2b).
Paynes Prairie is an extensive 9,000-acre fresh water marsh
that lies approximately 1.5 miles south of Biven's Arm. It provides
feeding grounds for the ibises near the nesting a^ea. Nesbitt et at.
(1974) also report stomach contents for 125 White Ibises nesting near
fresh water (21 from Biven's Arm). Crayfish were found in 45.3% of
the stomachs, insects (six orders) in 36.7%, and no crabs at all were
found. Fish constituted 0.7%, reptiles, 3.3%, and amphibians 1.2%.
Unlike the segregation observed on Sea Horse Key, the herons and
egrets nest in the same areas as the ibises on Biven's Arm. The entire
nesting area for all Ciconiiform birds is less than 10 acres. The red
maples reach a height of about 15 feet and the elders are less than 10
feet. This initial limitation on the number of potential nest sites
is accentuated by the presence of the competing herons, all of which


53
Nests were painted prior to the breeding season in the clearing
on Sea Horse in 1972. Of 25 painted nests, 22 were completely dis
assembled so that only the painted branch upon which they were constructed
the previous year remained. The remaining three were built upon and
used during the 1972 season. Along the south shore 25 nests were also
painted but the entire area was unused.
Over two winters 1000 nests were examined on Sea Horse and a
variety of parameters measured. Similar data were collected for all
available nests on Biven's Arm. Table 12 shows mean values and standard
deviations for nest heights, diameters, and nearest neighbors for the
two areas. Table 13 shows the percentages of nests in the various
tree species for both areas and the percentage of the total flora each
species constitutes. On Sea Horse the development of the vegetation
beneath the nests is extremely variable, ranging from a dense tangle of
vines to complete absence of flora. The branches upon which the nests
are constructed ranged from under 1/4 inch (for the clusters of vines
in which nests were found 8.6% of the time) to over three inches in
diameter (for the oak trees). Since the Biven's Arm birds nest in only
two species of trees, there is less variation here.
When local clusters of nests are considered on Sea Horse, however,
the variations in height, diameter, tree species, and nature of the
vegetation beneath the nest are much lower. Tables 14 and 15 show the
mean values and standard deviations for the nest height and diameter with
in each cluster, and the species of tree in which each cluster occurred.
In all 44 clusters the standard deviation of the height is less than the
overall value, and in 37 of the 44 clusters the standard deviation of the


Plate 7a. Male mounting female.
Plate 7b. Male treading (with back feathers erected).




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