THE BREEDING ECOLOGY OF FOUR SPECIES
OF HERONS AT LAKE ALICE, ALACHUA
DONALD ALISON JENNI
A DI.SERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARIHAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
PREFACE ANID ACKN OWLEDGI.C-ETS
In 1957, Florida was emerging from a severe drought. Tne long dry
period, coupled with the continuing destruction of long-legged wading
bird habit-it which has accompanied the development of Florida, seemed to
be bringing the numbers of long-legged wading birds to dangerously low
Officials of the Florida Audubon Society were greatly concerned over
this decline and as a result established a three year research grant to
support a study of the basic ecology of herons. Tr.eir interest made this
study possible and to this conservation organization I am deeply indebted.
I.-. John H. Storer and Miss Lisa Von Borowsky, president and vice-
president of the Florida Audubon Society generously shared with me the
benefits of their rany years of heron observations in Florida. Tne
National Wildlife Federation was also concerned and in 1959 awarded the
study a research grant, and to them I am. also indebted. The Florida
Acade.ry of Sciences awarded the study a research grant in 1959.
Access to Lake Alice was arranged with the cooperation of the staff
of the ALricultural Experiment Station. I appreciate the help of several
fellow graduate students who assisted in identifying food items and
accompanied ne on trips.
Chairr.an of my supervisory cormittee, Dr. J. C. Dickinson, Jr., was
of assistance thlroujout my work and I gratefully acknowledge his help.
Other members of my committee gave willingly of their time and counsel and
I especially appreciate their critical reading of tr.is dissertation.
Mary Jenni provided financial and moral support.
TABLE OF CONTENTS
PREFACE AND.ACKNOWLEDGMENTS. . . . . . .. ii
LIST OF TABLES ................... iv
LIST OF FIGURES . . . . . . . . .. v
INTRODUCTION .............. ...... 1
STUDY AREAS AND METHODS . . . . . . . 3
REPRODUCTION .................... 16
FEEDING . . . . . . . . . . . 58
COMPARISON OF REPRODUCTIVE HABITS OF TEE SPECIES . 78
COMPARISON OF THE FEEDING HABITS OF THE SPECIES . 95
CONCLUSIONS . .............. . 106
LITERATURE CI'ED . . . . . . . 113
BIOGRAPHICAL SKETCH . . . . . . . . 116
LIST OF TABLES
1. Frequency Distribution of Clutch Size of Snowy
Egrets, Lake Alice, 1960 . . . . . 25
2. Frequency Distribution of Clutch Size of Cattle
Egrets, Lake Alice, 1960 . . . . . 36
3. Frequency Distribution of Clutch Size of Little
Blue Herons, Lake Alice, 1960 . . . . 45
4. Frequency Distribution of Clutch Size of Louisiana
Herons, Lake Alice, 1960 . . . . . 53
5. Analysis of Fifty Pellets Regurgitated by Young
Snowy Egrets . . . . . . . . 63
6. Analysis of Fifty Pellets Regurgitated by Young
Cattle Egrets . . . . . . . . 68
7. Analysis of Fifty Pellets Regurgitated by Young
Little Blue Herons . . . . . . . 71
8. Analysis of Fifty Pellets Regurgitated by Young
Louisiana Herons . . . . . . . 75
9. The Species of Trees and Bushes Used By Four
Species of Herons for Nest Building at
Lake Alice, 1960 . . . . . . . 82
10. Nesting Statistics of Four Species of Herons at
Lake Alice . . . . . . . . . 84
11. Mortality of Eggs and Nestlings of Four Herons,
Lake Alice, 1960 . . . . . . . 93
LIST OF FIGURES
1. Temperature-rainfall relationships at Lake Alice,
averages of data gathered 1954-1961 (Anonymous,
1961) . . . . . . . . . . . 4
2. Map of peninsular Florida showing location of
heronries and other major points mentioned
in text . . . . . . . . . . 5
THE BREEDING ECOLOGY OF FOUR SPECIES OF HERONS
AT LAKE ALICE, ALACHUA COUNTY, FLORIDA
There is a large literature dealing with the herons and egrets.
Most of this literature consists of: (1) examples of unusual feeding
behavior in this highly adaptive group; (2) unusual geographic records
of these birds, which wander extensively after the breeding season;
(3) records of soft part colors, which appear to vary with the season
in at least some species; (4) discussions of their all-white coloration;
and (5) general observations on the location, size, and species composi-
tion of local and, sometimes, newly established heronries. In the last
decade the literature has been swelled by reports on the remarkable
range expansion of the Cattle Egret (Bubulcus ibis). But all this
literature does little to clarify the total biology of these birds.
Although we may never know as much about them as we know about the birds
that nest in more readily available places, there have been some recent
studies that aid greatly in our understanding of these birds.
Mayerriecks (1960) published a detailed discussion of the breeding
behavior of the Green Heron (Butorides virescens) and made an interest-
ing introduction to the comparative ethology of the Ardeidae by compar-
ing the Green Heron with four other species. Valverde (1955) studied
the large mixed heronry at Camargue, France, and has published the best
account of ardaid ecology to date. There have been a few reports on the
breeding behavior of various species. Noble and Schmidt (1938), Allen
- 1 -
and Mangels (1939), and Noble (1942) wrote about the Black-crowned
Night Heron (Nycticorax nycticorax), and Verwey (1930) published on the
Gray Heron (Ardea cinerea). Weller (1961) discussed certain aspects
of the post-laying breeding biology of the Least Bittern (Ixobrychus
exilis). There has been no systematic study of the ecology of a
mixed breeding colony.
Purpose of the Study
The most common herons of the Gainesville, Florida area, are the
Snowy Egret (Leucophoyx thula), Little Blue Heron (Florida caerulea),
Louisiana Heron (Hydranassa tricolor), and Cattle Egret. At the start
of my study these appeared to have basically identical ecology, except
for the conspicuously different feeding habits of the Cattle Egret.
My purpose was to gather information on the virtually unknown basic
breeding biology of these four species, to study their feeding behavior,
and finally to study the food habits. The aim was not only to learn
the facts, but also to learn something about the birds' interspecific
relationships, and their relationship to their environment, especially
to the most interesting but least known part of their environment, the
heronry. I hoped that such a study would provide information that
could help explain what a heronry is, what it provides the birds, and
would perhaps eventually help solve the intriguing problem of why even
undisturbed ardeids will abandon one area long used as a heronry to
breed in another as yet untried area. Though progress has been made,
a full and deep understanding of the heronry is still distant. We
need still to learn a great deal more about the lives of the individual
birds as well as the individual species, and especially we need to
learn the role of the heronry in their lives.
STUDY AREAS AND METHODS
Most of the observations reported here were made near Gainesville,
Alachua County, Florida, primarily at Lake Alice and Payne's Prairie,
but observations were made in many other areas. The climate of the area
is nearly semi-tropical and the long summers are hot and wet with high
relative humidity. The winters are short, mild, and considerably drier
than the sugars. The temperature usually goes below freezing several
times during the winter months. Figure 1 shows the temperature-rainfall
relationships based on averages of data obtained from 1954 through 1960
at the weather station adjacent to Lake Alice (Anonymous, 1961).
The Gainesville Area
Gainesville, just southeast of the center of Alachua County, Florida,
is located in the Central Highlands near the northern end of the Florida
Peninsula (Cooke, 1945) and is about midway between the Atlantic Ocean
and the Gulf of Mexico (see Figure 2). The area around Gainesville
supports a large number of herons. The terrain is mostly gently rolling
hills with innumerable ponds and sinks and with several large wet
prairies and lakes south of Gainesville. Pine flatwoods extend northeast
of the city. The elevation varies from a maximum of about 200 feet to
about 50 feet near which latter level lie the large wet prairies in the
southern part of the county. The area is underlain by limestone and part
of the uplands show karst topography. Practically all the soils are fine
sand originally derived from Coastal Plain sediments (Taylor et al., 1954).
AVERAGE MONTHLY RAINFALL IN INCHES
Figure 1: Temperature-rainfall relationships at Lake Alice, averages
of data gathered 1954-1961 (Anonymous, 1961).
SEA HORSE KEY
K LAKEPORT SPOILBANKS
Figure 2: Map of peninsular Florida showing location of heronries
and other major points mentioned in text.
There are three major types of vegetation: hardwood hammocks, pinelands,
and wet lands. The more hydric hammocks around the prairies and lakes
are characterized by magnolia (Magnolia grandiflora), water-oak (Quercus
nigra), laurel-oak (quercus laurifolia), and cabbage palm (Sabal
palmetto), and the more open upland hammocks by live-oak (Quercus
virginiana), hickory (Carya aquatica, and sometimes longleaf (Pinus
australus) or loblolly pine (Pinus taeda). There is practically no mesic
hammock in the area today; most of it has been cut over, and much of it
has been cleared for agricultural or other development. Northeast of
Gainesville there are extensive pine flatwoods dominated by slash pine
(Pinus palustris) and saw-palmetto (Serenoa repens) with numerous bald-
cypress (Taxodium distichum) and loblolly-bay (Gordonia lasianthus) ponds.
There are also flatwoods scattered throughout the area and a few undulat-
ing areas of longleaf pine (Laessle, 1942, and Taylor et al., 1954).
The extensive wetlands are responsible for the large heron population
in the Gainesville area; and the most important of these wetlands is
Payne's Prairie or Alachua Lake, which in recent years has been the
principal feeding area for herons around Gainesville. This nearly level
prairie varies from permanently flooded to, especially around the edges,
dry land. Much of it is covered with between one inch and two feet of
water, but during the wet summer season the water rises and covers
practically all the prairie. The vegetation of the deeper parts of the
prairie include water-hyacinth (Eichhornia crassipes), pickerel weed
(Pontederia lanceolata), arrowhead (Sagittaria spp.), and others, while
the shallower and seldom flooded parts of the prairie support dog-fennel
(Eupatorium spp.), maidencane (Panicum hemitomum), and a wide variety of
There are other wet prairies in the area.,,Levy Lakel-Ledvith Lake,
Tuscawilla Lake, Kanapaha Prairie, and Hogtown Prairie are the larger
and more important of these areas. They are all similar to Payne's
Prairie and they are covered with similar vegetation. The differences
between them are primarily due to different water depths. In addition
to these prairies there are extensive marshes and wetlands surrounding
Orange Lake, slightly farther south; and there are innumerable small
prairies, ponds, sinks, and marshy shore lines with vegetation similar
to the Payne's Prairie throughout the region. Practically all of these
areas are used by the herons for feeding, at least occasionally.
Heronries near Gainesville
Social herons have nested in at least three separate colonies in
the Gainesville area. A floating island, Bird Island, in Orange Lake
has supported a heronry for many years (Baynard, 1912). A moderate
sized group of herons bred in emergent trees and bushes in Bivin's Arm
Just south of Gainesville for many years (Dickinson, 1946). Since 1948
there has been a large mixed heronry at Lake Alice on the University of
Florida campus. In 1948 the herons failed to breed at Bivin's Arm and
have apparently never made any effort to re-establish themselves there.
These appear to be the birds that occupied Lake Alice. The vegetation
of these three areas is quite similar. The trees and bushes for the
most part are the same species. Besides their vegetation these three
heronries have other things in common. They are surrounded by water at
least several feet deep, there are alligator populations, and there is
practically no predation, and human disturbance is minimal. It is
apparently these factors plus the presence of suitable nest sites and
nesting material that were of prime importance in the original establish-
ment of these heronries. The less social Green Heron and Least Bittern
nest at several other localities around Gainesville in addition to these
Description of Lake Alice
Because most of the observations presented later in this report are
based on data gathered at Lake Alice, I shall describe this heronry in
more detail. Lake Alice was originally a small pond of about 10 acres,
but it fluctuated considerably (Dickinson, 1940). As the University of
Florida campus grew, surface runoff increased. In 1948 an earthen dam
was built just west of the "lake." The hollow where lay Jonah's Sink,
as it was formerly called, was flooded and the water spread out over an
area of about 90 acres. Included in this newly flooded area were a low
lying buttonbush (Cepalanthus occidentalia) marsh and the margins of an
extensive hammock of live oak, loblolly pine, and sweet-gum (Liquidamber
styraciflua), all of which were killed by the water. Buttonbush replaced
the hammock trees and wax myrtle (Myrica cerifera), willow (Salix spp.),
red maple (Acer rubrum), and elder (Sambucus simpeonii) invaded areas of
shallow water. Water pennywort (Hydrocotyle spp.) grew over the top of
the water throughout the swamp area, water-hyacinth grew over deeper but
still sheltered water. Pickerel weed, broad-leafed cattail (Typha
latifolia), smartweed (Polygonum spp.), and many other emergents invaded
the periodically flooded lake margins. What attracted the herons to
Lake Alice, at least what they used when they first arrived at the lake,
were the bushes and trees in which they nested. The species of bush or
tree did not appear to be of any importance; it appears that the only
thing the trees or bushes must provide the herons is a physically
suitable nest site. To be acceptable to herons for nest sites, the trees
must be located in a place difficult of access to predators. Thus
Florida heronries are usually on islands or over deep water.
Besides nesting in red maple, buttonbush, elder, wax myrtle, and
willow in Lake Alice, they nest elsewhere in Florida, in such diverse
vegetation as mangroves, cabbage palms, black gum, bald-cypress, maiden-
cane, and others. Thus it must be reasons other than the kinds of nest
trees available that caused the herons to nest at Lake Alice for the
first time. It appears most likely that what the lake offers is an
abundance of suitable nest sites sufficiently high above the lake surface,
over or surrounded by deep water, and with sufficient twigs for nests.
What caused the birds to abandon the other breeding area, Bivin's Arm,
is not clear (Mb6ht#,?l949).
During the years 1958, 1959, and 1960 the woody growth of Lake Alice
continued to die back; the only remnants of the old hammock being a few
huge oak stumps. Most of the buttonbush that was rooted in more than a
couple of feet of water was in poor condition and put out only a few new
twigs each year. By far the best woody growth in the lake during those
years was on the west bar, a shallow bar in the west end of the lake, in
other shallow areas near the middle of the south shore, and on the float-
ing islands. There are several floating islands in the southeast bay of
Lake Alice. It is on these islands and on the west bar that nearly all
of the birds have nested during these three years.
It was on the largest of these floating islands that most of the
quantitative data on the breeding ecology of the herons was collected in
1960. The island was anchored by the tree roots and was surrounded by
water six or more feet deep. The island raft was composed of living and
dead roots, which acted as the principal binding agent, and decayed and
decaying organic matter, which made up the bulk of the sub'rate. The
living plants, especially their roots and tubers, played a most important
role in maintaining the integrity of this island. Water pennywort grew
over most of the area and was the only ground cover in the heavily
wooded portions. A begonia (Begonia semperflorens) grew where there
was partial shade, and broadleafed cattail and water willow (Decondon
verticillatus) grew in exposed places. The water pennywort grows out
over the water for several feet around the edge where it is invaded by
water-hyacinth. Lush growths of water-hyacinth marks the positions of
ponds and channels which transected the study area. Red maple is the
dominant tree and occurs throughout the middle of the island. Button-
bush is as numerous but does not attain the size of the red maple and
occurs over the entire area, least abundantly around the edges. Wax
myrtle is not abundant and is scattered through the middle. Willow
grows mostly around the edge of the island where its large, irregular
trunks grow out over the water. Elder grows only in maximum sunlight
and occurs around the edges.
Ardeidae of Lake Alice
The ardeids that are known to have nested at Lake Alice include:
Green Heron, Little Blue Heron, Cattle Egret, Common Egret (Casmerodius
albus), Snowy Egret, Louisiana Heron, Black-crowned Night Heron, and
the Least Bittern. In addition Glossy Ibis (Plegadis falcinellus) and
White Ibis (Eudocimus albus) have nested there. The Anhinga (Anhinga
anhinga) also nests in association with the heronry. The Cattle Egret
first nested at Lake Alice in 1954 (Rice, 1956), and has nested there
each year since. Common Egrets have not nested there since at least
1958, and in 1960 for the first time the White Ibis did not remain at
Lake Alice to breed although they did appear early in the spring. Other
long-legged wading birds found at Lake Alice, but which are never known
to have nested there include Great Blue Heron (Ardea herodias), Yellow-
crowned Night Heron (Nyctanassa violacea), and Wood Ibis (Mycteria
During the 1960 breeding season, when the quantitative data on
reproduction and food habits were gathered, the populations of the
ardeids at Lake Alice were conservatively estimated as: Green Heron,
8 pairs, Little Blue Heron, 225 pairs; Cattle Egret, 300 pairs; Snowy
Egret, 275 pairs; Louisiana Heron, 150 pairs; Black-crowned Night
Herons, 2 pairs; and Least Bitterns, 12 pairs. Thus there were nearly
2,000 adult ardeids in the heronry during the nesting season. About
200 Glossy Ibis and 2,000 White Ibis roosted at the lake for a few days
early in the 1960 season, but only 2 pairs of Glossy Ibis built nests.
A few herons are found in the Gainesville area during the winter.
Although there was a winter roost at the east end of Payne's Prairie,
these birds roosted primarily at Lake Alice. During the three years, the
population began to build up after mid-February, and the adult population
reached its peak during April when most nesting was initiated. A few
birds fed at Lake Alice until nesting started, but after that the
adults no longer fed there. Later, the young fed around the edges of
the lake, especially near the heronry, but they continued to be fed by
the adults during this period. In the main most of the herons fed on
Payne's Prairie from the time they first arrived. One or two birds
usually fed at nearby sewage settling ponds. In addition, sinks, small
woods marshes, streams, roadside ditches, and other waters are occasionally
visited by foraging herons. When there was a sudden concentration of
food at one of these latter places, large numbers of herons congregated
As the young started flying and were able to move away from the
lake to feed, there was a movement of herons away from the Gainesville
area. The increase in the local heron population which must be expected
as a result of that season's production, was never more than temporarily
attained. Their numbers dwindled during late September and October,
and during late November or early December their numbers fluctuated
sporadically, probably as the result of southward migration. By mid-
December their numbers were greatly reduced and remained lower through
the winter than at any other season.
Although most observations were made at Lake Alice, Payne's Prairie,
and elsewhere in the Gainesville area, I studied herons at several other
places in Florida during 1958, 1959, and 1960. The more important of
these localities are shown in Figure 2. I made repeated observations
on the feeding behavior of herons breeding at Orange Lake, Marion County;
at Lake Griffin, Lake County; and at Snake and Sea Horse Keys, Levy
County. In addition I made three visits into the heronry at Lake Griffin
in 1960 and one visit each into the heronries at Lake Butler, Orange
County; Lake Okeechobee, Glades County; Tampa Bay, Hillsborough County;
and Snake Key, Levy County. Many additional casual observations not
included in this report were made at these and other Florida localities
outside the breeding season.
The method employed most was observation, often with binoculars or
telescope. Observations of adult behavior throughout the breeding
season were made from several vantage points around Lake Alice during
1958, 1959, and 1960. In 1960 detailed observations were made inside
the heronry. As each nest was found it was tagged with a number. The
tagged nests were visited daily and the condition of the nest, number
of eggs, or number of young was recorded. A piece of chrome plated tin
was attached at an angle to the end of a ten-foot pole and was used to
see into overhead nests. The eggs in nests that were low enough to reach
were marked with waterproof ink as they were laid and the fate of each
individual egg was followed. Two blinds were placed on the island and
were used occasionally.
During the 1960 season a total of at least 495 nests were tagged.
There was no way of identifying the owners of these nests at first, but
since they were kept under daily observation most of them were eventually
identified. However, many of these nests were not completed by the
adults, many others were destroyed before the identity of the adults
could be determined, and ownership of many nests was not determined until
the young hatched. At the end of the season, daily observation had been
made on a total of 275 successful, marked, and identified nests. This
niu*er included 102 Snowy Egret nests, 85 Cattle Egret nests, 58 Little
Blue Heron nests, and 35 Louisiana Heron nests. Observations on prac-
tically all of these nests extended from early nest building through
rearing of the young.
Observations of feeding adults were made primarily on Payne's Prairie
where most of the birds that nested at Lake Alice fed, and although it
was relatively unimportant as a feeding area, at Lake Alice. Study of
the herons' food habits was based on the analysis of material obtained
from nestlings and older, but still flightless, herons. These young
birds regurgitated their last meal when they were disturbed. The
amount of disturbance necessary to make them regurgitate varied not
only between species, but also between broods. Pellets of identifiable
food were preserved immediately in 10 per cent formalin. From one to
several days later the pellets were washed and transferred to 30 per
cent isopropanol. Later the food items were identified, counted, and
their volume determined by absorbing excess water with paper towels and
then measuring the volume of water the food displaced. Because of
possible distortion, volume is discussed as per cent of total volume.
Although many more pellets were collected, the discussion of food in
this report is based on the analysis of 50 relatively undigested pellets
recovered from young of each of the four herons.
Numerical data are usually presented as mean data. These figures
are followed by parenthetical statements of the size of the samples,
the range of the observations, and their standard deviations (abbreviated
as S.D.). Where it would be redundant, this parenthetical information
is not given. The standard deviation is included as a measure of the
dispersion of the observations about the mean. The inclusion of these
data serve as an indication of the biological significance of the means,
and give the reader additional information, and it was urged by Davis
(1955) for one, that when available this information always be included.
The "t" test is used to compare two means. In these tests, the
hypothesis is made that the two means are equal. The level of significance
is .05. When the hypothesis is rejected, it is assumed that the two
means are from different "populations." Statements regarding the
significance of the means are accompanied by the "t" values.
One species or several species may nest in a given heronry. When
more than one species nests, as at Lake Alice, it is called a mixed
heronry. The term rookery, though often applied to heronries, is the
name of a place where Rooks (Corvus frugilegus) nest and is not properly
applicable to herons. In this chapter the breeding activity of the
four most numerous herons at Lake Alice is described. Following the
three introductory sections which deal with all four species of herons,
are individual accounts in which the statistics of each species are
Winter Status and Spring Arrival
Herons winter in large numbers in south Florida, but are noticeably
less abundant along the northern Florida coasts and along the Central
Highlands. Although the Gainesville area is marginal as a wintering
area for ardeids it is not far distant from acceptable wintering habitat.
The abundance of ardeids in the Gainesville region during the winter
fluctuates drastically and appears to be related to the weather espec-
ially temperature. During December and early January there are fewer
birds in the area than at other times. After a few days of lowered
temperature, or two or three nights of freezing temperature, practically
no Snowy Egrets, Little Blue Herons, or Louisiana Herons can be found.
After about a week or ten days of average temperature, or after several
days of above average temperature, and later, with the approach of
spring, their numbers gradually increase and mixed flocks of 100 to 300
or more roost at the lake. Present observations indicate that the
Cattle Egret is not going to follow this general pattern, but rather
will use Lake Alice as a regular winter roost. Through the winter
of 1959-1960 approximately 100 Cattle Egrets, and in 1960-1961 approxi-
mately 250 Cattle Egrets roosted at Lake Alice. These wintering birds
fed in different places than did Cattle Egrets during the breeding
season; they followed different local flight paths, and roosted in a
part of the lake not used for breeding by any species of heron during
the 1958, 1959, or 1960 seasons.
During February, or even as early as late January, the number of
herons roosting at Lake Alice begins to increase. There is a gradual
build-up until a maximan is reached about the time nesting begins.
Throughout this period the birds fly directly to the roost where the
individuals remain quiet and seldom move about except for an occasional
conflict over a perch. Occasionally a whole group of birds will take
flight and move to a different part of the lake to roost, but in the
evening later in the season, the individuals are very active when they
arrive at the roost.
Onset of Breeding
The first activity which seemed to be related to the onset of
breeding was the increased restlessness of roosting birds. In mid-March
individuals started flying around within the roosting area. There did
not appear to be any directiveness to this new behavior. The birds did
not seem to be engaged in any productive effort and their behavior
apparently only reflected a general restlessness. Another change at this
time was the return of a few birds to the heronry as early as two hours
before sunset, and, in the morning, a few stayed long past the departure
of most of the other birds. These individuals perched in the bushes
and trees part of the time but spent most of their time "exploring"
the heronry, hopping from limb to limb and making short flights from
one part of the heronry to another. After only one or two days the
males centered their activities around a particular bush or tree and
their short flights brought them back to this place. They directed
threat displays at every heron that approached them closely, regardless
of species. Here they eventually performed the courtship displays.
The males did not feed in these areas and had to leave them unoccupied
when they left to feed. After pair formation one of the pair always
remained in the now established territory.
When they first became more sedentary, the males spent most of
their time defending that place by directing threat postures at and
attacking other individuals. Although this primarily hostile behavior
has sexual implications, the males' behavior changed and became primarily
sexual after one to several days of hostile behavior. It is not clear
whether this shift in behavior was due to other birds avoiding the area
defended by males or to continued development of the males' sexuality,
but it was probably brought about by both. The most impressive and
most complex sexual display is the Stretch Display, described in detail
by Meyerriecks (1960). The male has established his territory when he
begins performing the Stretch Displays, but may leave during mid-day and
in so doing he runs the risk of losing that territory. The Stretch
Display is apparently common to all herons, but there were interesting
differences.in the way the display was performed by each of the four
species studied. This was the primary sexual display that attracted
females. A male of any of these species which performed a series of
Stretch Displays with vigor and with bold movements was soon surrounded
by a group of his kind (although sexes of the individuals in the group
were unknown to the observer later behavior indicated that the group
usually included at least one female.) When an individual approached
too close, the male interrupted the displays long enough to drive that
individual away and then returned to his perch and resumed the Stretch
Displays. A female ready for pair formation would repeatedly approach
the male and then retreat from him as he came at her in a threatening
attitude. The male would eventually not threaten the female and the
pair bond was established. Within a few days of pair formation the
birds started distinguishing between individuals flying through the
territory and those actually invading the territory, and they ignored
The breeding behavior of herons has been investigated by others and
a detailed discussion of their comparative breeding behavior is beyond
the scope of this study. Published reports on heron breeding behavior
include Meyerriecks' comparison of several species (1960), detailed
descriptions of Black-crowned Night Heron behavior by Noble and Schmidt
(1938) and by Allen and Mangel (1940), and an exhaustive report on the
Gray Heron by Verwey (1930).
Sequence of Nesting
Although most of the birds arrive four to eight weeks before the
start of breeding, and there appears to be no substantial difference in
the time the four species arrive at Lake Alice, the species do start
nesting at slightly different times. Practically all Louisiana Heron
nesting is confined to the early part of the season. In 1960, 94 per
cent of all clutches were completed before April 28, most of them
during the first two weeks of April. Most Little Blue Heron nesting
was also confined to the early part of the season. Sixty-seven per
cent of the Little Blue Heron clutches were completed by April 28 but
about 30 per cent of the Little Blue Heron clutches were not completed
until between mid-May and early July, mostly during the last three
weeks of June. Snowy Egrets also started nesting early in the season,
but unlike the Louisiana and Little Blue Herons which had completed
most of their clutches during the first two weeks of April, the Snowy
Egrets completed most of their clutches during the last two weeks of
April. Eighty-seven per cent of all of their clutches were completed
by April 28, and although a few new nests were built throughout the
season, the rate of new nest construction decreased rapidly after the
first peak. Cattle Egret nesting started about the time the Snowy
Egrets reached their peak, that is about two to three weeks after the
other species started nesting, and the Cattle Egrets reached their
peak two weeks later than did the Snowy Egrets; 64 per cent of all
Cattle Egret clutches being completed by May 12. Additional Cattle
Egret clutches were completed throughout the season and there was
a second peak of activity during the first half of July. Cattle Egret
nesting effort was more equally distributed throughout the season
than were nesting efforts of the other species. The last Cattle Egret
clutch in the study area was completed July 15. Some were completed
even later elsewhere in the heronry.
Snowy Egrets built their nests on the sturdiest sites available in
the territories which had been established by the males. The first
territories established in each new area of the heronry as it expanded
during the season were those few areas that included remnants of old
nests. Old nests offered especially sturdy places to preen, court,
copulate, and eventually nest, and were consequently in great demand
by all species of herons. If available in the territory a neat left
over from the previous year was used as the base for a new nest.
Next in importance as nest sites were limbs. The main trunk of
the tree was used as a support for one side of the nest, and the
structure was built out on two limbs.
The third most common nest site was in the basket-like growth that
had formed at the stubby end of some trunk as a result of herons break-
ing off nesting material in previous years. Some species broke twigs
off living trees, and when the terminal shoot, especially of wax myrtle,
is thus pruned, growth of limbs immediately below that point is stimu-
lated. The result is the basket-like structure which makes a very
sturdy nest site. Less exploited nest sites included horizontal limbs
such as those commonly used by Little Blue Herons.
The average height at which 96 Snowy Egret nests were built in
1960 was 5.7 feet above the heronry floor or the lake surface (range
3-11 feet, S.D. 1.33). Snowy Egrets built more of their nests in
red maple (43 per cent of all nests in 1960) than in any other tree or
bush. Buttonbush was second (26 per cent) in importance and elder, willow,
and wax myrtle were used for 18, 7, and 6 per cent of the nests respec-
The nesting substrate of Snowy Egrets in Florida is described as
cypress and mangrove swamps and buttonbush ponds (Howell, 1932) and
willow islands (Bent, 1926). Elsewhere they build their nests in red
eedar (Wilson in Bent, 1926), prickly pear and huisache and reeds
(Bent, 1926). The nests are placed on the lower limbs from 8 to 12
feet above the water (Howell, 1932), in willows of 8 to 15 feet (Bent,
1926); but nests on Vingt-une Island, Texas, were built very close
to the ground or at heights up to 5 or 6 feet. In coastal mangrove
heronries, such as Snake Key or the Alafia River spoilbanks on the
west coast of Florida, the nests were much higher than at Lake Alice
and higher than those mentioned in the above reports; the lowest
nests were about 8 to 12 feet above the ground.
Nesting material was gathered only by the male and brought to the
female who worked it into the nest. When the twig-carrying male was
a few feet from the female he elevated his crest, drew his neck into
an "s" curve and elevated his aigrettes. The female responded with
a similar feather movement, reached out and took the twig in her bill.
Both birds immediately sleeked their plumage as the female turned
directly to the nest with the twig. As nest building progressed the
intensity of this display diminished until the birds no longer elevated
the aigrettes, but they usually continued to elevate the crest. The
female normally held the stick near the middle. Several efforts were
usually needed to push it into the nest, pushing, sometimes getting it
part way lodged and pulling it out again, until it was well anchored.
The twig was dropped frequently, but the male usually found it on one
of his later trips.
All the sticks were gathered from the ground or shallow water
beneath the heronry. Howell (1932) commented that Snowy Egret nests
are built of dead twigs. The usual pattern followed early in the
season before vegetation became rank was for the male to return directly
to the ground from the nest and walk around until an acceptable twig
was located. Often several were picked up and rejected and on occasion
attempts to pick up tree roots or branches of large limbs were observed.
The male walked back to the nest tree and climbed up to the nest if
there were suitable footholds, otherwise a big hop and a short flight
of two or three wingbeats brought him close enough to the nest so
that he could pass the twig to the female. Increased growth of vegeta-
tion altered this pattern later in the season, and the male had to fly
a short distance.
All the twigs in some nests were coated with mud. As the season
progressed, females of all species accidentally dropped sticks which
they were working into their nests, and some nests were torn apart by
the wind or other herons and scattered on the ground beneath the heronry.
Wresh twigs, some still with green leaves, became as abundant on the
heronry floor as were the old mud-coated ones, and later in the season
they were more available than the other twigs. These new twigs were
used according to their availability and Snowy Egret nests built later
in the season were easily distinguished from older nests.
The pair spent from three to six days, rarely as many as eight
days, building the nest before the female started laying; the average
for 21 nests was 4.1 days (range 3-8, S.D. = 1.15). Nest building
continued through egg-laying, especially the first two or three days,
but the nest was usually completed by the time the last egg was laid.
The gradual but continual loss of twigs during incubation was offset
by the addition of new material.
Egg Laying and Clutch Size
Snowy Egrets laid their eggs before 9:00 in the morning. The
first egg was laid from three to eight days after the adults started
building the nest but the nest was seldom completed by then. The first
egg often passed down into or through the nest; and occasionally the
second egg was lost this way. The second egg was laid an average of
1.8 days after the first egg, and the other intervals were 2.0 days
between the second and third eggs, 1.9 days between the third and fourth,
and 1.8 days between the fourth and fifth eggs. The over-all average
was 1.9 days between eggs (114 intervals, range 1-2 days, S.D. = 0.34).
This data is in agreement with Dawson (1915) who on the basis of
hatching pattern, concluded that the eggs are laid on alternate Adays.
At Lake Alice the most frequent two-day interval was between the second
and third eggs. Intervals of more than two days were not recorded.
Typically there was only one, one-day interval per nest, and the fifth
egg was the egg most frequently laid one day after its predecessor.
The adults spent an average of 7.3 days in egg laying (average number
of eggs laid times the average interval).
Snowy Egret clutches at Lake Alice (see Table 1) contained an
average of 3.9 eggs (102 clutches, range 2-5, S.D. = 0.67). Howell
(1932) reports the clutch as three or four, but Bent (1926) says the
clutch is ordinarily four or five, sometimes only three and rarely six.
Early clutches, that is those completed between April 4 and April 28,
averaged 4.1 eggs (89 clutches, range 3-5, S.D. a 0.48), but late nests
contained substantially fewer eggs. Clutches completed between April
Table 1.--Frequency Distribution of Clutch Size
of Snowy Egrets, Lake Alice, 1960
April 4 to April 28
April 29 to June 16
29 and June 16 averaged 2.9 eggs (13 clutches, range 2-4, S.D. 0.62).
These late nests are probably all renesting attempts of birds whose
earlier attempts failed. The difference between the means of the
early and late clutches is significant at the .01 level ("t" = 7.79).
The average number of eggs laid in nests that eventually contained
complete clutches was 4.1 (100 nests, range 2-8, S.D. 0.64), but
some eggs were lost before the clutch was completed and additional
eggs were certainly lost before they were recorded.
There is no evidence that any of the Snowy Egrets raised two
broods at Lake Alice. The nesting season is sufficiently long for
raising two broods, but nesting activity decreased rapidly and contin-
uously after the initial peak, and there was no evidence of a late
second peak of activity. At least one brood of two young was raised
from the age of a few days by only a single parent at Lake Alice during
1960, and it might be reasoned that one parent could be relieved from
care of the first brood and start a second. However, even nest building
behavior demands two birds: a male to hunt twigs and deliver them to
the nest site and a female to take the twigs and fashion a nest from
them. Protecting a nest against depredations of other nest building
herons and protecting the eggs from predators also require the presence
of two individuals.
Snowy Egrets usually started incubating the day after the second
egg was laid, or sometimes they started the day the third egg was laid.
Although there was considerable variation, the adults seldom incubated
one egg, sometimes incubated two eggs, but always started incubating
by the time the clutch contained three eggs. The pattern of hatching
of the young indicates that effective incubation may actually have
begun somewhat earlier than observations of adult behavior indicated.
These observations conflict with Dawson's (1915) statement that, on
the basis of hatching pattern in three nests, incubation starts with
the laying of the first egg.
The incubation period averaged 22.4 days (39 nests, range 21-24
days, S.D. 0.75). The most frequent incubation periods were 23 and
24 days with 21 and 12 observations respectively. Three nests hatched
in 22 days. The incubation period of 18 days reported by McIllhenney
(1912) is the only one quoted by Bent (1926), and is the figure given
by Sprunt and Chamberlain (1949). Eighteen days is approximately the
duration from the laying of the last egg to the hatching of the first
young at Lake Alice. At Lake Alice both sexes incubate, and Bent (1926)
has reported this for other localities. Although the Snowy Egret nest
is an open network of twigs offering little protection from below
against cold or wind, there appears to be no correlation between clutch
size or weather and length of incubation period. The nest is important
to the adults for several activities, but all it offers the eggs is
protection from falling to the ground.
Hatching and the Young
The chicks could usually be heard calling inside the egg for two
or more days before they pipped. The young may hatch completely in
less than 24 hours, but most young pipped at least one day before they
hatched. The young are covered with a moderate amount of white down
which dries in a short time.
On the first day of hatching, the nests contained one or two,
rarely three chicks, and they averaged 1.5 (80 nests, range 1-3, S.D.
= 0.62). The second day of hatching most nests contained two or three
chicks, a few contained one, and about half as many contained four as
contained one. They averaged 2.4 chicks the second day (68 nests,
range 1-4, S.D. = 0.76), an average of nearly one per nest hatched
between the first and second day. About half the nests had three on
the third day and most of the others had two or four. They averaged
2.9 chicks on the third day (59 nests, range 1-4, S.D. = 0.85). How-
ever Dawson (1915) found three nests in California in which the young
hatched on alternate days, a sequence not observed at Lake Alice.
An average of 3.3 young hatched per nest (91 nests, range 1-5,
S.D. 0.96). It took an average of 3.2 days (75 nests, range 1-6,
S.D. 1.14) for all to hatch. The hatchlings were able to lift their
heads for only a moment at a time during the first two days. On the
third day they could keep the head elevated for considerable time and
were often heard peeping. After a few days they became silent when
The parents brooded the young for several days, one parent nearly
always on the nest. Bent (1926) reported that both adults care for
the young, but one of them always remains at the nest. At Lake Alice
especially during mid-day and in June and July broods, the adults spent
much of their time standing over the young shading them. Mcllhenny
(1912) provides an excellent photograph of an adult shading young. Both
parents feed the young, but until the young were old enough to hold
their heads up and strike at foreign objects that came to the nest, one
of the parents always stayed at the nest while the other hunted and
brought food to the chicks. After the young were about one week to 10
days old, the parents no longer stayed on the nest through the day.
After this time both parents started hunting and bringing food to the
young at the same time.
At first the young picked food off the floor of the nest where
it had been regurgitated by the adults. After a few days, they quickly
passed through a stage of taking the food from the parents' bills, the
several young grabbing for the bill at one time. The young next pro-
gressed to the procedure of sticking their heads into the bill and
mouth, reaching down into the throat and intercepting the regurgitated
food on its way up. In broods that hatched over a period of several
days the oldest young might thus be taking fish out of its parents'
throat while its youngest sibling was still too weak to hold its head up.
Mortality of Eggs and Young
The loss of eggs from nests between the time of laying and the
start of hatching was at least 5.4 per cent. During the hatching process
there was a mortality of 14.7 per cent. From egg laying through hatch-
ing there was an over-all minimum mortality of 19.3 per cent.
The average number of hatchlings surviving until two days after
the last young hatched was 3.0 (86 broods, range 1-5, S.D. = 0.97),
this is significantly fever than hatched ("t" 1.67). The brood size
was reduced still further to an average of 2.7 chicks by seven days
after hatching (77 broods, range 1-5, S.D. z 0.86), and two weeks after
the last young hatched, an average of only 2.2 young survived per nest
(65 broods, range 1-4, S.D. = 0.84). These losses are greater than
those of the first two days. After two weeks the first hatchlings were
often able to leave the nest and later estimates of mortality are
unreliable. The reduced number of observations of older broods is due
in part to intentional termination of observations at some nests. The
total mortality during the first two weeks of nest life was 32.6 per
cent. The over-all loss exceeded an average of one chick per nest;
of the 3.3 that hatched, an average of 2.2 chicks per nest survived
for two weeks. Practically all this loss was due to starvation. The
last chick to hatch was considerably behind the earlier ones in
development and size and was incapable of successfully competing with
four siblings and often incapable of competing with three. As each
day passed the older nest mates developed and grew while the youngest
waned until eventually it died of starvation.
Nests that contained four chicks two days after hatching had an
average of only 2.5 chicks two weeks after hatching. Broods that
contained three chicks two days after hatching were reduced to an
average of 2.3 by the end of their second week, and broods of two were
similarly but much less drastically reduced to 1.8 checks. Thus 1.5
young were lost from broods of four, 0.7 were lost from broods of
three, and less than 0.3 were lost from broods of two. It appears
that the adults were able to feed and raise a maxim=w of about 2.5
young per nest. Of the 31 nests in which four or more young hatched,
only two nests held as many as four two weeks later. The young that
started were usually trampled into the nest by their siblings, but were
occasionally ejected from the nest. The minimum over-all loss of both,
eggs and young from egg laying through the first two weeks of nest life
was 45.6 per cent.
There was a sharp increase in mortality when the young first left
the nest and started climbing around in the bushes and trees. At Lake
Alice the trees and bushes were short and scrubby, and those young
who fell to the ground were usually, but not always, able to get
back to their nests. The young were extremely agile and used their
heads and necks as prehensile aids in climbing. Nevertheless, during
1960 I found two large Juveniles hanging dead. One was upside down
with the foot caught and the other was caught by the wing. Young
that wandered into the nest site of nearby birds were attacked,
especially if the neighbor was a Cattle Egret, and were driven or
knocked from the tree.
Old nests were seldom available in Cattle Egret territories
because other species had already established territories to include
the old nests before the Cattle Egrets started nesting. But Cattle
Egrets occasionally built on top of a nest formed earlier in the
season by some other heron and later abandoned by it. Some of the
Cattle Egrets which started nesting as late as June or July were able
to use nests recently abandoned by young Snowy Egrets or Little Blue
Herons. Cattle Egrets were the last to breed and generally acquired
territories and nest sites higher in trees and bushes than did the
other species. As a result there was less stable support for their
nests. Heron territories at Lake Alice had definite vertical as well
as lateral limits. The most favored nest site appeared to be in the
basket-like growth of limbs which resulted from the breaking off of
terminal twigs for nest material in previous years. Cattle Egret nests
were often built against the tree trunk on a pair of small limbs, in
the fork of a horizontal limb, which gave support in three directions
from the nest center; or between the two branches just beyond the
fork. These nests were quite stable. Another frequent site was on a
cross formed by two limbs, often where a dead tree had fallen over on
a live one.
The average height of 76 Cattle Egret nests in 1960 was 7.8 feet
(76 nests, range 5.5-12.0, S.D. = 1.39). Many of their nests were
placed in either red maple (33 per cent of all nests) or in buttonbush
(29 per cent). Elder was also used frequently (19 per cent of the
nests) and wax myrtle and willow were used least (12 and 7 per cent,
Cattle Egrets breed in a variety of sites throughout their extensive
range. This species builds its nests in reed beds in East Africa
(Mackvorth-Praed and Grant, 1957) and from 50 to 80 feet up in eucalyp-
tus trees in South Africa (Skead, 1956). Whistler (1949) says that
in India they often nest at considerable heights. However, in Africa
and India and throughout their range they most commonly nest at less
than 20 feet. In Japan they nest 10 to 20 feet from the ground in the
low branches of trees, shrubs, or bamboos (Austin and Kuroda, 1953),
and in their generalization Witherby et al. (1947), say Cattle Egrets
usually nest in trees and bushes growing in water but that they also
nest in big cork-oaks on dry ground, on rocky islets, and in big trees
in towns in Egypt.
Nest material was brought to the females by the males. This was
the typical sequence: the male landed near the female, stretched his
neck, and proffered the twig to the female; the male usually landed
quite close to the nest but sometimes had to take a step or two, or
hop down one more limb, before passing the twig. The male elevated the
crown and back feathers and sometimes the chin feathers as he offered
the twig; the female elevated her feathers, took the twig, sleeked her
plumage as did the male, turned to the nest, and pushed the twig into
the nest. The female laid the first few twigs in a little pile, but
worked later twigs into the nest by trial and error. She accidentally
dropped many. Although Witherby et al. (1947) say that both sexes
build the nest, Skead (1956) says that one bird gathers the nesting
material, but the other does the actual building, my observations
confirming the latter.
The male flew directly to the upper parts of trees and bushes after
delivering a twig to the female. He broke off twigs, but unlike the
Snowy Egret never descended to the heronry floor to pick up twigs lying
there. Skead (1956) says that in South Africa they gather material from
the ground or pull it from the trees. The dead, brittle twigs were
broken off by the earliest nesting Cattle Egrets and Little Blue Herons.
The twigs broken off by later nesting individuals were live and tough.
The male spent much time looking for a twig he could reach. He would grab
it in his bill, pull back on it, jerk it, pull back, lean back precar-
iously flapping with his wings, recover his perch, give it another jerk,
and often fail to break it off.
At first the males gathered twigs from the bushes and trees within
the heronry. They soon exhausted this supply, and started foraging
farther from the nest site. By mid-season, Cattle Egrets were gathering
twigs from bushes and trees around the lakeshore and from distant parts
of the lake. Late in the 1960 season a few males gathered sticks more
than a half mile south of Lake Alice and flew back to the lake with them.
The birds gathered a few twigs about the heronry throughout the season as
the vegetation continued to grow.
Nest building continued for an average of 6.6 days (26 nests,
range 3-11 days, S.D. = 1.88) before the first egg was laid. There
was considerable variation in the rate at which sticks were added to
the nest. In some nests a few sticks were gathered and nothing more
was added for several days, while in others the bulk of the nest was
completed within two or three days. The adults continued to add a
few twigs to the nest during early incubation; nests were essentially
complete early in the egg-laying period, and subsequent twigs were
added for repair and maintenance of the nest.
If one member of each pair was not always present at the nest
throughout and following construction other herons, which were always
on the prowl for nest twigs, dismantled the nest. Many birds added
substantially to their nests every day up to egg laying. A few birds
completed their nests several days before the female laid the first egg.
Egg Laying and Clutch Size
Cattle Egret nests were fairly complete when the females laid their
first eggs, and they seldom lost these first eggs because of poor nest
construction. The eggs were typically laid before 9:00 in the morning.
The interval between egg laying was two days; the interval was deter-
mined between the first and second eggs 29 times, second and third eggs
38 times, third and fourth eggs 20 times, and fourth and fifth eggs
The clutches averaged 3.5 eggs (85 clutches, range 1-6, S.D. -
0.69). The number of eggs in each nest is summarized in Table 2.
Clutches completed between mid-April and mid-May averaged 3.6 eggs (64
clutches, range 3-5, S.D. = 0.58), and those completed between mid-May
and mid-July averaged 3.4 eggs (31 clutches, range 1-6, S.D. = 0.99).
The late clutches thus are both slightly smaller in average size and
slightly more variable in size (see also Table 2), however they are
not significantly smaller ("t" = 0.84). Cattle Egret clutch size
appears to vary throughout its range, it is given as: three to five
in Japan (Austin and Kuroda, 1953), one to three in East Africa,
three to five in South Africa (Mackworth-Praed and Grant, 1957), two
or three in South Africa (Skead, 1956), four or five in India (Whistler,
1949), and four or five, six occasionally, is given as a generaliza-
tion by Witherby et al. (1957).
Late broods were not smaller than the early ones. There was no
evidence that any of the Cattle Egrets raised two broods. Although
nesting extended over a long enough period to allow a few of the
earliest to nest again, very few pairs did nest at the end of the
season, and they were more likely pairs which started late in the first
place and failed with their first attempts.
Incubation at Lake Alice, as in South Africa (Skead, 1956), was
by both sexes. Observations indicate that incubation began in all
nests with the first egg. Typically however, one young hatched in each
nest the first day. The second day a second one hatched in about half
the nests. Since the second egg was always laid two days after the
first, it follows that if incubation started when the first egg was
laid the second egg should have hatched two days after the first.
Effective incubation apparently began the day the first egg was laid
in about half the nests, and the day after the first egg was laid in
the other half. This was probably delayed in many nests because the
adults spent much of the first day adding twigs to the nest.
Table 2.--Prequency Distribution of Clutch Size
of Cattle Egrets, Lake Alice, 1960
1 2 3 4 5 6
Total number of nests 1 3 41 33 6 1
April 15 to May 12 0 0 28 22 4 0
May 13 to July 15 1 3 13 11 2 1
The average incubation period of the Cattle Egret was 22.9 days
(30 nests, range 22-23, S.D. = 0.24). Incubation was 22 days in two
clutches and in the remaining 28 nests required 23 days. According to
Witherby et al. (1947) the incubation period is 21-24 days. Skead
(1956) gave the incubation period as 26 days, which would be about the
time from the laying of the first egg to the hatching of the last young
in clutches of two or three which he observed.
Hatching and the Young
The young could be heard calling inside the egg for a day or two
before they hatched. They often pipped the day before they hatched.
Sometimes they pipped two, or rarely three, days before hatching. The
young dried off rapidly. They were covered with a moderate amount of
white down, and had a fairly well pronounced crown.
The first day of hatching the Cattle Egret nests averaged 1.1
young (49 nests, range 1-2, S.D. = 0.28); 45 of 49 nests contained one
and the other four nests held two chicks each. The second day of hatch-
ing the nests averaged 1.6 young (41 broods, range 1-3, S.D. = 0.58);
they averaged 2.1 on the third, 2.6 on the fourth, and 3.0 on the fifth
day. In general terms, the nests averaged one chick the first day and
increased at an average rate of one every other day thereafter. This
correlates with the rate at which the eggs were laid. About half the
first-laid eggs hatched one day before, and half hatched two days before
the second egg hatched, but all later eggs hatched one every other day.
An average of 3.2 young hatched per nest (73 nests, range 1-5,
S.D. = 0.81). The average hatching time was 4.7 days per nest (41 nests,
range 1-8 days, S.D. = 1.83). The adults continued to brood the young
for several days after hatching started. Skead (1956) also noticed that
there was little change in adult behavior when the young first hatched.
In many nests the last young hatched seven or even eight days after the
first one, and the adults were not able to incubate continuously during
the day for that period of time because the oldest siblings were large
and required considerable food. The combination of high air tempera-
ture and large siblings was obviously sufficient to provide warmth to
carry the eggs through the last few days of incubation. The "peck-
order" that Skead (1956) noted in Cattle Egret broods was probably
the simple dominance of larger over smaller nestlings. During mid-day
brooding of the young chicks and eggs consisted mostly of shading them
in practically all the late nests. The parent stood over the nest with
the body at a right angle to the sun's rays, often with the wing nearest
the sun drooped and shading the young.
At first the young were too weak to do more than lift their heads
momentarily. They spent their time resting and picking food up from the
floor of the nest. After a few days they could hold their heads up and
take food directly from the parent's bill. From this time on they spent
most of the daylight hours sitting up in the nest with the wings partly
extended, the bill open, and the gular pouch fluttering. As with the
Snowy Egret, the young were soon able to reach down into the parent's
gullet and remove food before the parent could regurgitate it.
Mortality of Eggs and Young
Adult Cattle Egrets were extremely attentive and seldom lost any
eggs from their nests. From egg laying to the day before hatching
mortality was only 3.9 per cent. Occasionally a predator took all the
eggs from a Cattle Egret nest, but these nests could have been ones
that had been abandoned already, or the adults might have abandoned
them when they did lose an egg to a predator. Very few clutches were
so lost. The hatching mortality was 7.0 per cent, and the minimum
over-all mortality of eggs from laying through hatching was 10.7 per
There was little loss of nestlings (2.5 per cent) during the first
two days that followed the hatching of the last individual. The brood
was reduced to 3.0 young (66 broods, range 1-4, S.D. = 0.79) at the
end of the first week, and further reduced to 2.9 young (52 broods,
range 1-4, S.D. = 0.80) by the time the youngest chick was two weeks
old. The differences between the numbers alive at hatching, two days
later, one week later, and two weeks later are not significantly differ-
ent, but the number alive two weeks after hatching is significantly
less than the number hatching ("t" = 1.78). The mortality of nestlings
during their first two weeks was 8.2 per cent. The minimum mortality
from egg laying through two weeks of age for the youngest nestling was
17.9 per cent.
There was considerable loss of young when they started climbing
around in the trees. If they climbed into the nest of an incubating
Cattle Egret they were peaked until they left or fell from the tree.
Although I never saw the adults kill a young bird, I occasionally saw
blood on the young, especially their wings, after such encounters. The
nesting vegetation was low and dense at Lake Alice, and young Cattle
Egrets that fell to the ground were usually able to get back to their
nests. Those that wandered about before attempting to return to the
trees frequently fell prey to alligators. In South Africa, young Cattle
Egrets that fell to the ground were unable to get back to their nests
(50 feet and higher) and starved (Skead, 1956). In 1960, at least five
young Cattle Egrets between three and four weeks old were eaten by
alligators around one small pond in part of the Lake Alice heronry.
Skead (1956) says that in South Africa "eagles" take the young and
"cause great consternation in the colonies." Another unusual cause
of mortality was the paralysis of many nestlings which occurred only
during one year in the heronry which Skead (1956) observed.
Little Blue Heron
Little Blue Herons built their nests in the territories established
by the male, and they usually built them on the perch he had used for
courtship. The favored site for both courtship and nest building was
an- old nest. However, Meanley (1955) says the Little Blue Herons
he studied did not use the old nests that were available. At Lake
Alice Little Blue Herons were often the first birds to move into and
breed in previously unoccupied parts of the lake. The males moved into
these areas, established territories that included the few nests of the
previous year, using them as platforms where they performed their
stretch displays, and preened. Those unable to find such favored
sites usually built their nests on small horizontal limbs wedging it
against the main trunk. Less common nest sites included forks of
large horizontal limbs, places where two branches crossed, or some
place where they could lodge the first few twigs.
The average height of Little Blue Heron nests in 1960 was 7.2 feet
(49 nests, range 4.5-10.5, S.D. = 1.41). However, Little Blue Herons
had two distinct peaks of nesting activity in 1960: in the early peak,
clutches completed before April 28, the average nest height was 6.7
feet; in the later period, most clutches completed between June 10 and
June 30, the average nest height was 8.5 feet. Little Blue Herons
showed strong nest site preferences; they built 49 per cent of their
nests in red maple and 36 per cent in buttonbush. They built few
nests in elder (11 per cent) or willow (4 per cent) and built no nests
in wax myrtle.
According to Howell (1932) Little Blue Herons build their nests
in willow, wax myrtle, and, in northern Florida, in titi (Howell, 1932).
Willowv and other bushes (Bent, 1926), buttonbush and swamp privet are
used in Arkansas (Meanley, 1955). Box elder, water maple, overcup oak,
and elm are sites in Tennessee (Ganier, 1960), and nests are built in
catalpa in Oklahoma (Tomer, 1955). Most of the nest sites just described
are over water or on islands, but the catalpa tree heronry in Oklahoma
was on dry land. Bent (1926) says that on the willow islands of the
upper St. Johns River in Florida the Little Blue Herons nest in bushes
on the outer edges of the islands, from two to four feet above the
ground. Howell (1932) says the nests are built from four to eight feet
above water. In the woods described by Ganier, most nests were between
16 and 25 feet up. In Arkansas Little Blue Herons build their nests
closer to the shore than do the other species, and build them at an
average height of eight feet (range 3-15 feet) with other nests placed
up to 25 feet (Meanley, 1955). In the catalpa woods they nested 9-18
feet above the ground (Tomer, 1955).
The males gathered the nesting material, twigs and small branches,
and brought it to the females who built the nests, and Meanley (1955)
reported the males gathering sticks and passing them to the females in
Arkansas. At Lake Alice the male flew to nest, and landed close enough
to it that he could pass the twig to the female. The male lowered the
head, extended the neck, and pointed his bill toward the female who
reached out and took the twig in her bill. The male usually turned
around immediately and left, but would sometimes remain near the nest
and preen or would sometimes move over into the nest with the female.
The female turned to the nest with the twig, and if the nest was just
being started she would lay the twig on top of the others. If the
nest was nearly complete she pushed the twig into the nest from the
side. While working twigs into the nest, she frequently dropped them,
and at the peak of building the ground beneath Little Blue Heron nests
was often littered with twigs.
The male collected nest material by breaking twigs off bushes and
trees. Male Little Blue Herons collected twigs at all levels throughout
the heronry, but primarily from the upper halves of the trees and bushes.
In Arkansas, Meanley (1955) found they occasionally break off twigs,
but usually gather twigs from the shallow water beneath the nest. At
Lake Alice the males few from tree to tree, grabbing, pulling, shaking,
and attempting to break off any one of several twigs before successfully
getting one. Each flew directly to his territory with the twig,, landed
near and usually above the nest, hopped down to the nest, and passed the
twig to the female. Because Little Blue Herons nested earlier than the
Cattle Egrets, practically all their nests were complete before twigs
became scarce, and the males were able to gather all their nesting
material in the general vicinity of their own territory. As they wandered
about searching for nesting materials, the males took twigs from any
nests that were left unguarded by other birds. Only a few twigs could
be pulled from any nest before the whole thing came apart and fell to
Nest construction continued into the egg-laying period but was
generally completed by the time incubation started. The bulk of the
material was added to the nest before the first egg was laid. The
adults worked on the nest for 4.8 days (12 nests, range 3-8, S.D. .
1.41). Meanley's (1955) statement that nest construction requires,
"three to five days, occasionally six or seven days," falls within
the range for the Lake Alice birds. Nests were built fairly rapidly
at a rather uniform rate, but the birds occasionally had to abandon
one site in favor of another a foot or two distant because the place
first selected offered an inadequate base for the nest. The first egg
was often laid in a very small nest, and in such cases the nest was
usually completed with two more days of building. Most nests were
obviously "completed" on the third or fourth day. Sticks added later
merely reinforced the structure.
Egg Laying and Clutch Size
The female Little Blue Heron laid the first egg from three to eight
days after starting the nest. Although a small proportion of nests were
not complete at that time, eggs were lost through the nest only occasion-
ally. The eggs typically were laid before 9:00 in the morning. They
were laid at a rate of one every 1.7 days (48 intervals, range 1-2 days,
S.D. = 0.47). The interval between laying the first and the second egg
was 1.7 days, the interval between the second and third egg was 1.7
days, and the interval between the third and fourth egg was 1.7 days.
There was one interval of one day in 12 of the 18 nests that eventually
held three or four eggs, in the other six nests all intervals were two
days, and in one nest with five eggs the intervals between the first
and second and the fourth and fifth eggs were one day. Meanley (1955)
seems to have noted that eggs are sometimes laid on consecutive days
and not always on alternate days because he says that they are,
"deposited on an average of one nearly every other day."
The clutches contained an average of 3.7 eggs (58 nests, range
2-5, S.D. a 0.73). An average of at least 3.8 (56 nests, range 2-6,
S.D. 0.69) eggs were laid in nests that eventually held complete
clutches, but some were lost before incubation started. The number of
eggs in each clutch is summarized in Table 3 According to Bent
(1926) the Little Blue Heron usually lays four or five eggs, sometimes
only three and occasionally six, and according to Howell (1932) they
usually lay four or five eggs. Meanley (1955) gives an average of
4.04 eggs for 50 nests with a range of from three to five eggs. Few
Little Blue Heron clutches were completed between April 26 and May 21,
1960, any place in the heronry, and there was no new nesting activity
in the study area during this period. Clutches completed earlier,
from April 3 to April 26, averaged 4.1 eggs (39 clutches, range 3-5,
S.D. = 0.48). Clutches completed between May 21 and July 4 averaged
2.9 eggs (19 clutches, range 2-4, S.D. : 0.45). This difference is
also seen in Table 3. The late clutches were significantly smaller,
"t" 9.07. The reasons why there were no new nesting efforts for a
three-week period are vague. The small size of the late clutches is
common to many species and was discussed by Lack (1954), and although
the adults brought different food to their nestlings after mid-June, the
Table 3.--Frequency Distribution of Clutch Size of
Little Blue Herons, Lake Alice, 1960
Total nest for the season
April 1 to April 28
April 29 to July 4
explanation for the smaller clutches is unknown. Most of these late
nesting efforts were apparently renesting efforts.
It is highly improbable that Little Herons raised two broods at
Lake Alice. A few late nest efforts were started about the time the
parents of the earliest broods finished feeding their young. Chronologi-
cally it was barely possible, but it is not likely that only the few
pairs nesting earliest might raise a second brood, and that they could
do so immediately after the first brood became independent. There
were more early nesting efforts interrupted than were there late
nesting efforts started.
In many nests the first egg laid was the only egg which opened on
the first day of hatching; but by the second day of hatching three
eggs had usually hatched. It appears then that incubation started the
day after the second egg was laid or the day the third egg was laid.
Adult behavior at the nest indicated that they did not begin to incubate
until after there were two eggs in the nest, and that they nearly always
were incubating a nest with three eggs. These observations agree with
Meanley's (1955) observation that incubation virtually always begins
after the laying of the second egg. At Lake Alice, however, the frequent
hatching of the first egg one day before the others indicates that it
had received at least one more day of effective incubation than had any
of the others.
The incubation period for 19 clutches averaged 22.8 days (range
22-25 days, S.D. = 0.73). Eight clutches had an incubation period of
22 days, eight had a period of 23 days, one took 4 days, and two clutches
required 25 days. The two clutches that required 25 days were the only
five-egg clutches for which I obtained incubation periods; but there
appears to be no correlation between clutch size and duration of
Both parents incubated the eggs. Published incubation periods
agree with the Lake Alice data, Meanley (1955) saying that incubation
is done by both sexes and is 22 to 24 days, 22 or 23 days is the rule,
and Sprunt and Chamberlain (1949) give the incubation period as 21 to
Hatching and the Young
The young called in the egg for a day or two before they hatched.
They usually pipped one day before they hatched. However, they occasion-
ally hatched the same day they first pipped, and rarely pipped two or
three days before hatching. The young dried shortly after hatching as
did young of the other species. They are covered with a moderate amount
of down which is white except for the short crest which is a dingy, pale
The first day of hatching most nests contained one young, some had
two, and a very few had three. The first day the nests averaged 1.6
chicks (37 nests, range 1-3, S.D. 0.69). The second day most nests had
three, a few still had one or two and a very few had four; the nests
averaged 2.5 young (33 broods, range 1-4, S.D. 0.95). The third day
the frequency of nests with four increased and the broods averaged 2.9.
An average of 3.2 Little Blue Herons hatched per nest (51 nests,
range 1-5, S.D. = 1.00). Hatching of the entire brood required an average
of 3.2 days (31 nests, range 1-7, S.D. 1.42). The young were weak
and inactive for the first few days, and were unable to raise their
heads more than briefly. Within a few days they could hold their heads
up for long periods, and called frequently. The adults continued brood-
ing until the young could hold themselves upright. The most obvious
change in adult behavior at hatching was an increased restlessness,
some individuals stood up and looked at the young, moving around a
great deal. Others changed behavior but little. The young first fed
by picking up food the adults regurgitated into the nest, but later took
food from the adult's bill, and at about 10 to 14 days reached down into
the adult's gullet for the food.
Little Blue Herons lost few eggs once they started incubation. The
mortality from egg laying until just before hatching was 3.9 per cent.
There was a loss of 12.1 per cent during hatching. The total mortality
from egg laying through hatching exceeded 15.6 per cent. Meanley (1955)
does not give comparable data for the Arkansas heronry he studied, but
he says that robbing the nests of sticks by other herons and egrets is
the principal cause of egg loss.
Although an average of 3.2 eggs hatched per nest, there were only
3.0 young per nest two days after the last egg hatched (47 nests, range
1-5, S.D. = 0.91). This is not significantly less than the number at
two days ("t" = 0.98), and they were still further reduced to an average
of 2.4 by the end of the second week (40 nests, range 1-4, S.D. 0.76),
the difference between the last two figures is significant ("t" 2.17).
Some of the young started leaving the nest at this time. An average of
nearly one young per nest (0.8 young, 47 nests, range 0-4, S.D. = 0.65)
was lost during the two weeks following hatching. The nestling mortality
was 26.2 per cent. Practically all these losses were due to starvation
of the smallest and youngest hatchlings. Young that hatched as late as
four or five days after the first young had hatched seldom developed
rapidly enough to be able to successfully compete with their older
siblings. Of 30 Little Blue Heron nests that lost young, 23 nests
lost one, and 6 nests lost two, and 1 lost four. Meanley (1955) says
that their nest mates push them out. He also implicates raccoons,
house cats and Black Vultures as predators, none of which appeared to
be so at Lake Alice.
Causes of high mortality that occurred when the young left the
nest were difficult to evaluate. Most of those that fell out of the
trees were able to get back into them. The day after an extremely
heavy rainfall, (3.55 inches on June 18, 1960) I found two nearly dead
young on the floor of the heronry. Their feathers were wet and packed
with mud and their wing feathers had been pounded into the mud by the
rain. The next day they were gone and had not returned to the nest
tree. One chick about three weeks old was attacked by nearby adult
herons of several species when it invaded their nesting territories.
It was bleeding on the wing and back and appeared to be very weakened;
and it disappeared during the next night.
Louisiana Herons also built their nests in the territories estab-
lished by the males. It was usually placed where the male held his
courtship displays. This is probably because the male selected the
steadiest site available within the territory. The nest site was often
an old nest if one occurred in the territory. Such relatively scarce
sites were preferred by most other herons at Lake Alice. However, the
Louisiana Heron was the first species to start nesting and established
its territories to include most of the few old nest platforms available.
Birds renesting later in the season were often able to take over
abandoned nests. If the territory did not include an old nest, they
usually built in the sturdiest place available. Louisiana Herons
established territories with comparatively secure perches and seldom
The average height of Louisiana Heron nests in 1960 was 5.7 feet
(30 nests, range 3.5-7.5, S.D. 0.96). Louisiana Herons built 39
per cent of their nests in elder. They also nested frequently in button-
bush (29 per cent) and in myrtle (18 per cent of all nests) but they
seldom nested in red maple, or willow (11 and 7 per cent, respectively).
In Florida, Louisiana Herons are said to nest in willows, mangroves,
buttonwoods, and rushes (Bent, 1926, Howell, 1932). In Texas, Bent
(1926) records them nesting in these, and also in cane, mesquite,
husiache, and occasionally in prickly pear. The nest height in one
Texas heronry is given as one to two feet; and in another heronry as 10
to 15 feet (Bent, 1926). Howell (1932) gives the nest height of Florida
birds as 2 to 20 feet, but on the upper St. Johns River Bent (1926)
says they build their nests in the middle of the heronries at heights
of 2 to 12 feet, and in the Cuthbert Lake heronry they build their
nests throughout the heronry at 6 to 12 feet above the ground.
Nesting material was gathered and brought to the female by the
male. When returning with nesting materials the male alighted next
to the nest and usually a little above it. As he settled to the perch
and folded his wings he elevated his aigrettes and offered the twig to
the female. She elevated her aigrettes as the male landed, and took
the twig from him. They both then lowered their aigrettes. The male
occasionally remained at the nest to preen and rest before going after
more twigs. The female immediately turned to the nest with the twig,
and by trial and error usually found a place for it. Huxley (notes
quoted in Bent, 1926) says that in Louisiana, the male "usually,
perhaps always," finds the sticks, and the female does the actual build-
Early in the season, nesting material was gathered from the ground
beneath the heronry. The male usually picked up dead twigs, and often
several were picked up and rejected before one was carried to the nest
site. He occasionally broke twigs off large fallen limbs and small
bushes and would wander quite far from the territory in this search.
After passing the twig to the female he immediately searched far.other
twigs, and having found a good place to gather them would fly directly
to that spot from the nest. Late nests included twigs with fresh
leaves. These could have been broken off by the male, or they could
have been wastage from nests of other species, which was not determined.
Nest construction was a continuing affair with Louisiana Herons,
but the bulk of construction occurred during a period of four to six
days, (occasionally up to eight days early in the season, or later as
short as three days). Usually five days passed before the eggs were
laid. The male brought the bulk of the nest material during the first
three days. By the end of the third day most nests were nearly of
their maximal size. The birds added fewer sticks to the nest during
the next two days. During this time the nest became more compact as
they worked the twigs into the nest structure, and it acquired a more
bowl-like shape. The adults continued to add to the nest during egg
laying and incubation, but the amount of material brought in waned as
incubation progressed. A bird might grab a nest twig and jiggle it
or force it farther into the nest whenever it was on the nest.
Egg Laying and Clutch Size
Louisiana Herons laid the first egg about four or five days after
the nest was started. The nest was large and nearly complete by this
time. Eggs were laid before 9:00 in the morning. The average interval
between laying was 1.7 days (40 intervals, range 1-2 days, S.D. = 0.65).
The first and second eggs were laid on consecutive days about half the
time and on alternate days about half the time (average 1.6 days), but
the frequency of two-day intervals increased with each successive egg.
The average interval was 1.7 days between the second and third eggs
and 1.8 days between the third and fourth.
The Louisiana Heron clutches averaged 4.1 eggs (35 nests, range
3-6, S.D. 0.66). A few eggs were lost before incubation started and
an average of at least 4.3 eggs were laid (35 nests, range 3-9, S.D. z
1.04). The number of eggs in each clutch is shown in Table 4. Howell
(1932) gives the clutch as three to five which agrees well with the
Lake Alice data, but Bent (1926) says they "usually lay four or five
Table 4.--Frequency Distribution of Clutch Size
of Louisiana Herons, Lake Alice, 1960
3 5 6
Total nests 4 22 9 1
eggs, sometimes three, occasionally six or very rarely seven" which is
more than they lay at Lake Alice. There was an indication that late
clutches at Lake Alice tended to be smaller, but only a few late nests
were found, not enough to permit any generalization. The Louisiana
Heron was the first ardeid to start nesting, and a high per cent of its
early nests were successful. Egg laying was finished in 33 of 35 nests
by April 27. The two late clutches were finished May 2 and May 20.
Louisiana Herons did not raise two broods.
Louisiana Herons at Lake Alice seldom incubated one or two eggs,
but were usually incubating when the nest held three or more eggs.
The start of incubation, which was variable for all four species, was
most variable in the Louisiana Heron. The first day of hatching a few
nests contained three young. In some clutches only one chick hatched
on the first day, and in a few of these the pattern of hatching indicated
that incubation started the day before the second egg was laid. In
clutches of five eggs there were usually four chicks by the third day
of hatching, and most of those that did not have four had three. Incu-
bation most frequently started the day before the penultimate egg was
The incubation period for 10 clutches averaged 23.8 days (range
23-25 days, S.D. = 0.60). Three clutches hatched in 23 days, six
clutches in 24 days, and one took 25 days. The 25 day clutch contained
five eggs as did two of the 24 day clutches, but no conclusions can be
drawn from the data. The widely given incubation period of 21 days is
credited to Audubon (1840) by Bent (1926). Both parents incubated.
Hatching and the Young
The young called inside the egg for a day or two before they hatched.
Typically they pipped the day before they hatched. The adults dropped
the empty shells over the edge of the nest. The young dried off quickly.
They are covered with a moderate amount of white, dark brown, and
almost black down. The down faded slightly before the young acquired
The first day of hatching most Louisiana Heron nests contained one
young, but some nests held two or three. They averaged 2.2 chicks the
first day (25 nests, range 1-3, 8.D. = 0.86). The next day most nests
held three, a few had two or four, and a very few still had one. They
averaged 2.7 chicks on the second day (23 nests, range 1-4, S.D. = 0.86).
On the third day most nests had three or four, a few still had two, and
they averaged 3.1. The fourth day they averaged 3.1 young, and finally
on the fifth day the fifth young hatched in some nests.
An average of 3.7 young hatched per nest (29 nests, range 2-5, S.D.
* 0.78). Hatching took an average of 3.4 days per clutch (24 nests,
range 2-5, S.D. = 1.11). Four was the most frequent number of young
hatching, three was next most frequent, and a few broods contained five
or two young. At least one young was lost from every nest in which five
young hatched. Considering broods of all ages three was the modal number
Louisiana Herons brooded continuously until the young were several
days old. Since they bred early in the season they only occasionally
needed to shade either the eggs or the hatchlings. There was little
apparent change in adult behavior at hatching except that the birds seemed
to move around on the nest more. Both parents continued brooding. When
the young were several days old, by which time the youngest was large
enough to hold up its head, the adults left them alone while they both
hunted for food. The adults continued to brood the chicks at night.
Until the young were a few days old they were unable to hold up
their heads more than momentarily. During this period they spent most
of their time resting. They fed by picking up food the adults regurgi-
tated into the nest. After they became able to hold their heads up
they were able to take food directly from the parent. By the time they
were about two weeks old they could reach into the adult's gullet and
seize the food on its way up.
Mortality of Eggs and Young
Although some eggs were lost before incubation started only a few
eggs were lost during incubation. From laying until just before hatch-
ing egg mortality was only 3.9 per cent. The hatching mortality was
10.5 per cent, and the minimum mortality during laying, incubating, and
hatching was 14.0 per cent.
The average number of hatchlings surviving until two days after the
last one hatched was 3.4 per nest (30 nests, range 1-5, S.D. 1.08),
this is not significantly less than the number that hatched ("t" =
1.31). The number was further reduced to 3.1 by the seventh day after
hatching (31 nests, range 1-5, S.D. = 0.85), which is not significantly
less than the number alive at two days ("t" = 1.09). Two weeks after
hatching an average of 2.8 young survived (31 nests, range 1-4, S.D. -
0.77), which is not significantly fewer than were alive at one week
("t' = 1.63). However, the number of young alive decreased significantly
between the second day after hatching and two weeks ("t" = 2.59). Some
older young started leaving the nest when the youngest was about two
weeks old and later estimates of losses were less reliable. One chick
(0.94) was lost per nest (27 nests, range 0-3, S.D. 0.71) during the
first two weeks of nest life, a nestling mortality of 18.3 per cent.
Most of this loss was due to the starvation of the youngest chick in
many clutches. When the last chick hatched as late as five or more
days after his oldest sibling he started nest life at a severe disad-
vantage. While the young were small and feeble the adults regurgitated
food onto the floor of the nest from which the young picked it up.
When two or three of the nestlings developed to the point where they
went to the parent, reached down into its throat and took the food, the
nestling only strong enough to pick food off the nest floor usually got
none. Typically only one young starved in a nest (17 of 19 nests in
which young starved) but in two nests two did; and in about one out of
every three nests none starved.
Another peak in mortality occurred when the young left the nest and
started climbing about in the bushes and trees. In spite of their
agility and tenacity a few fell to the ground, but at Lake Alice where
the vegetation was low and bushy most of those individuals got back into
the nest trees. Occasionally one became hung in the trees. One I found
dead in 1960 had fallen during a storm from the top of a particularly
high nest and landed on its back in a narrow fork of a branch where it
died. Bent (1926) also found young that had become entangled in the
vegetation and died, but he also notes that the young climb and swim well.
A cursory comparison of the feeding behavior of the herons on
Payne's Prairie and in other feeding areas around Gainesville indicates
that these birds are all feeding essentially the same way; that is,
they are wading around in shallow water catching and eating small
animals. The notable exception is the Cattle Egret which regularly
feeds in company with cattle on higher and usually drier ground. How-
ever, any comparative generalization on their foods must be based on
an analysis of food habits.
When they become excited or are disturbed, young herons often
regurgitate their last meal, which they cast up as a pellet. By
systematically collecting these pellets it is possible to acquire a
series of heron meals without collecting the birds. The technique has
two distinct advantages. (1) Because a large series of pellets is
potentially available, the collector can reject pellets which show
advanced or even moderate digestion, and (2) especially with less common
species, pellets can be repeatedly taken from the same individuals. When
the heronry is full of flightless young it should be an ecologically
significant time to study the food habits of the herons, because in order
to feed themselves and their young the adults must gather substantially
more food per day than at any other time of the year.
- 58 -
Food apparently is abundant in the Gainesville region during the
time of year the adults were feeding young because at that time plant
growth was rapid, temperatures were high, Band water levels were up.
In spite of a probably adequate supply of food, an average of nearly
one young per nest starved to death in nests of three of the four
heron species studied. The adults' need for food for themselves and
their ravenous young exceeded their food catching ability. It seems
reasonable to assume that the birds were operating near their maximal
efficiency. If this is true the birds were probably catching the kind
of food they could catch the most of and were searching for it in the
places where it was most often available to them. Differences in
feeding behavior and in food habits would probably be amplified during
this period of stress while the adults are feeding young.
Feeding Behavior of Adults
The feeding behavior of the various herons was strikingly similar.
In most of their feeding activities they employed certain basic techniques
which are common to all species. Each species employed its own varia-
tions of these techniques and the frequencies with which each of the
several techniques was used varied among the four species.
The Ardeidae are opportunistic birds, not only as a group, but also
as individual species and as individuals. They take advantage of a wide
variety of food sources and employ a variety of feeding patterns to
catch food. They are quick to take advantage of an abnormal bounty, and
groups composed of several species would gather around any temporary
concentration of food. Although there are many interesting variations,
practically all feeding behavior of adult herons around Gainesville falls
into three general, though not necessarily distinct categories.' (1)
Stand and Wait; (2) Wade or Walk Slowly; and (3) Active Pursuit. The
first two categories (names from Meyerriecks, 1960) are specific types
of feeding behavior and are typical of the herons. These two types show
several modifications; but the more unusual and dramatic means of
gathering food are mostly variations of Active Pursuit.
In the Stand and Wait type of feeding, the heron finds a likely
place, poses his body in readiness, and remains motionless. The heron
remains immobile and eventually makes a strike if food approaches; if
not it moves to a new place. The body may be held low and horizontal
with the ankles flexed and the neck slightly withdrawn in a soft "s"
curve; or the body may be held upright, the feet and legs straight,
and the neck extended. Herons will hold these positions for many minutes,
but may sometimes change from one of them to the other.
) The Walk or Wade Slowly type of feeding has many elements in
common with the Stand and Wait type, and resembles a slow moving variant
of Stand and Wait. Walk or Wade Slowly is the fundamental stealth
technique and is an important part of the feeding repertoire of many
herons. The body may be held horizontal with the neck slightly with-
drawn and the bill pointed forward; or the body may be upright with
the neck straight and the bill pointed downward at about a 45 degree
angle. The body, neck and head are usually held rigid as the heron
moves, but the neck sometimes bobs slightly with each step, or Just
before making a strike the head may be withdrawn slightly or it may
be undulated sideways. As the bird moves, each foot is lifted, extended,
and lowered quite deliberately; the body is simultaneously moved
smoothly forward. The bird may "freeze" Just before a strike. Birds
hunting by the Stand and Wait technique often feed in the Wade and Walk
Slowly technique while they are moving from one stand to another.
Active Pursuit includes Meinertzhagen's (1949) type, Disturb and
Chase; but the most frequent form of Active Pursuit in the Gainesville
region is simply walking or running in shallow water, chasing fish and
making strikes here and there. A frequent ploy of several species is
to walk through fields, or along the edge of a pond, or any likely
place catching insects, frogs, or fish that flush at the heron's approach,
This differs from Wade or Walk Slowly in that the body is not held
horizontal or rigidly, the neck is not necessarily held rigid but typi-
cally moves forward and backward with each step; in other words the
bird is not "sneaking up" on anything, but only catching what it sees
and this is most often something which is moving out of the heron's way.
The birds use many other types of Active Pursuit, and these form the
basis of the many notes published on "unusual" heron feeding behavior;
but these more unusual feeding patterns are used only infrequently by
the Lake Alice birds during the breeding season. Reaching down and
taking food from the water while on the wing (Hovering of Meyerriecks,
1960) is one of the more frequent of these unusual types, and has been
reported in the Gainesville area (Dickinson, 1947).
Adult Snowy Egrets employ the Stand and Wait techniques of feeding
more than any other feeding method. They also commonly feed by use of
the Wade or Walk Slowly technique, sometimes feeding thus in grasslands
away from water. During the suniers Snowy Egrets occasionally associated
with cattle. They would walk along near a cow and catch prey disturbed
by it very much the way Cattle Egrets feed. While with cattle, Snowy
Egret behavior appeared to be intermediate between merely walking along
and flushing prey and Wade or Walk Slowly. Snowy Egrets, more often
than any of the other herons, fed by some form of Active Pursuit.
They would frequently dash about through very shallow water twisting,
turning, stopping and taking off in new directions, striking here and
there at the fish. Snowy Egrets would often interrupt more deliberate
types of hunting to chase after fish in shallow water and sometimes
would run along a fairly steep canal or stream bank.
Snowy Egrets are social feeders and many individuals would gather
to feed in a small area where there was a local abundance of food. Groups
of 5 to 25 or sometimes more, often congregated around culverts and
along small streams following heavy rains and a rise in the water level.
Young Snowy Egrets readily regurgitated their last meal when dis-
turbed. Nestlings only a few days old did not become as distressed as
did one to two week old young when they were disturbed, and they did
not usually regurgitate. If one sibling was much less developed than
his nest mates, he often ate the food his older and more excitable
siblings regurgitated into the nest. Snowy Egret pellets were compact
and held together rather well. If the young had been fed recently, each
typically produced two pellets when disturbed.
The contents of the 50 analyzed pellets were: fish 87.8 per cent
by volume, invertebrates 7.1 per cent, and amphibians 4.8 per cent.
Table 5 lists the prey taken, the total number found in all 50 pellets,
and the per cent of the total volume of each prey item. A total of 46
amphibians were eaten and 35 of them were tadpoles. These were particu-
larly small tadpoles and taken altogether they comprised only 2.9 per
Table 5.--Analysis of Fifty Pellets Regurgitated by
Young Snowy Egrets
Number Per Cent of
Oligochaeta 1 tr.
Astacidae 6 0.70
Palaemonetes spp. 7 0.28
Zygoptera 7 0.06
Anisoptera (5 nymph) 18 1.00
Locustidae 188 2.78
Tettigoniidae 99 1.47
Gryllidae 32 0.47
Hydrophilidae 15 0.17
Corixidae 4 0.04
Arachnida 1 0.04
unidentified tadpoles 19 1.21
Acris gryllus 10 1.06
unidentified Hylid tadpoles 14 1.28
unidentified Rana spp. tadpoles 2 0.43
Rana pipiens 1 0.85
f-lasoma spp. 42 1.08
Enneacanthus gloriosus 2 1.49
Enneacanthus obesus 12 5.31
Esox americanus 15 8.29
Etheostoma barratti 21 1.06
Fundulus chrysotus 37 6.80
Gambusia affinis 456 36.14
Heterandria formosa 224 3.08
Jordanella fToridae 195 20.83
Lepomis macrochirus 8 2.34
Leptolucania omuata 1 0.04
Lucania goodei 9 0.21
Micropterus salmoides 3 1.23
cent of the total diet. A few cricket frogs (10 Acris gryllus) and one
leopard frog (Rana pipiens) were taken.
Grasshoppers and crickets (Locustidae, Tettigoniidae and Gryllidae
combined, 4.8 per cent) were only about as important in the over-all
diet as were the amphibians. Most of the pellets contained a few
insects, and 2 of the 50 contained no fish but were composed entirely
of insects and amphibians. Dragon-flies (Anisoptera) were also import-
ant invertebrate food; five nymphs and 13 adults being taken. A few
crayfish and fresh-water shrimp (Astacidae and Palaemonetes spp.) were
included, especially early in the season.
Mosquitofish (Gambusia affinis) was the most important as well as
the most numerous prey taken. Flagfish (Jordanella floridae) was second
most important. Each of the other prey species was much less important
in the total diet than were these two. Redfin pickerel (Esox americanus)
was third, the golden topminnow (Fundulus chrysotus) was fourth, and the
banded sunfish (Enneacanthus obesus) was fifth in over-all importance.
Six other species were less important, comprising from 1.1 to 3.1 per
cent of the diet. One of these, the least killifish (Heterandria
formosa) was the second most frequently taken prey species, 224 indiv-
iduals were included in the 50 pellets.
The pellets averaged 29.0 individual prey items. They included an
average of 0.9 amphibians, 7.6 invertebrates, and 20.5 fish. The most
important prey species, mosquitofish, flagfish, redfin pickerel, golden
topminnow, and banded sunfish, comprised 77.2 per cent of the total diet.
Mosquitofish were included 456 times in the 50 pellets and the least
killifish was the second most numerous prey with 224 individuals taken.
In addition to the 50 pellets discussed above, at least 200 other pellets
were studied in the heronry, but were not collected, and another 24
pellets that were collected are not included in the analysis. These
additional gross observations tend to verify the preceding observations.
According to Baynard (1912), 50 pellets regurgitated by young
Snowy Egrets at Bird Island, Orange Lake, contained 120 small suckers,
762 grasshoppers, 91 cut-worms, 2 small lizards, 29 small crayfish,
and 7 small moccasins. Because Snowy Egrets from Orange Lake feed in
places similar to those where the Lake Alice birds feed, it is diffi-
cult to explain the differences in food. Baynard's taxonomic categories
are too vague to allow careful comparisons.
During the breeding season Cattle Egrets fed in grasslands and
open meadows, and although they occasionally fed in wet places, they
mostly fed away from water. They fed by walking along near the head or
side of a grazing cow and caught prey flushed by the cow. However, they
would occasionally wander from cow to cow, or even less frequently they
would take short excursions away from a cow, and at these times they
caught food they disturbed themselves. Individual Cattle Egrets would
occasionally feed by themselves, independent of large ungulates, but
although frequently noted during the winter this method of feeding
was relatively uncommon during the breeding season.
Cattle Egrets are social birds and nearly always fed in small
groups. Early in the season they usually fed in groups of 5 to 25
individuals, but in the middle of the nesting season, when many of the
adults were feeding young, they most often fed in small groups of up
to five or six individuals.
Young Cattle Egrets readily regurgitated their last meal when they
were disturbed, and they were more easily disturbed than were the other
species. When one young started regurgitating, the other young in the
tree immediately started regurgitating, and 25 or 30 pellets would
quickly rain down out of a tree. The pellets appeared to be composed
almost entirely of grasshoppers with an occasional small frog or snake.
The pellets were very neatly packed and were held together by mucous.
If they had been fed recently, most young Cattle Egrets would produce
The 50 pellets studied were composed of invertebrates 63.2 per
cent by volume, amphibians 32.3 per cent, and reptiles 4.4 per cent.
The analysis of the 50 pellets on which this discussion is based is
presented in Table 6. Reptiles are relatively unimportant, only three
snakes are included in the 50 pellets.
Amphibians were an important part of the diet of young Cattle Egrets.
The 50 pellet sample included 101 frogs and toads. The leopard frog
was the most important amphibian volume-wise although it involved only
23 individuals as compared with 69 individuals of the volumetrically
second ranked cricket frog. One eastern spadefoot (Scaphiopus holbrooki)
was included. Eight other individual amphibians were recorded: four
treefrogs (Hyla spp.), two narrow-mouthed toads (Microhyla carolinensis),
and two unidentified frogs. Together these eight individuals contri-
buted only 2.0 per cent to the total diet. These, as well as the
spadefoot were probably accidental and incidental in the diet.
Short-horned grasshoppers (Locustidae) are the most important prey
of Cattle Egrets. Locustids were found in 48 of the 50 pellets. The
other two pellets were each composed of one large leopard frog. Crickets
(Gryllidae) were the second most important invertebrate prey, but
contributed less volume to the diet than did leopard frogs. The third
most important invertebrate, long-horned grasshoppers (Tettigoniidae)
were less important than even the cricket frogs. Collectively, the
orthopteran insects contributed 56.6 per cent of the diet by volume.
Spiders (Arachnida) were taken regularly; 88 were included in this
sample. The other invertebrate groups (Table 6) each contributed less
than 1 per cent of the diet and appeared to be taken accidentally.
The pellets contained an average of 34.1 prey items: 0.1 snakes,
2.0 amphibians, and 32.0 invertebrates. The four most important prey
groups, short-horned grasshoppers, leopard frogs, crickets, and
cricket frogs, comprised 78.8 per cent of the total diet.
In addition to the 50 pellets discussed at length above, 50 more
were collected, and about 500 more pellets were studied in the heronry,
but not collected. For the most part these observations essentially
verified what has been already said and only add a few species to the
list of prey. The most unusual pellets found were a group of about
eight pellets collected on June 23, 1960. They were composed entirely
of 30 to 50 mm., terrestrial beetle larva (Coleoptera).
Except for occasional single-stomach analyses, there appear to be
no previously reported quantitative reports on Cattle Egret food.. Their
diet is described as very varied, practically omnivorous (Mackworth-
Praed and Grant, 1957). Other than this one report, the Cattle Egret is
recognized as primarily being a grasshopper feeder. Grasshoppers are
noted as being of first importance in India (Whistler, 1949), in South
Africa (Skead, 1956), and throughout its range (Witherby et al., 1947).
Table 6.--Analysis of Fifty Pellets Regurgitated
by Young Cattle Egrets
Number Per Cent of
Zygoptera 1 0.01
Anisoptera 5 0.58
Locustidae 679 36.21
Tettigoniidae 279 6.85
Gryllidae 523 13.50
Coleoptera 10 0.17
Elateridae 1 0.01
Curculionidae 2 0.01
Diptera 3 0.12
Tabanidae 5 0.54
Lepidoptera 2 0.12
Arachnida 88 5.15
Scaphiopus holbrooki 1 1.25
unidentified frogs 2 0.83
unidentified Hylidae 2 0.42
Acris gryllus 69 13.29
Hyla spp. 2 0.42
Rana pipiens 23 15.78
Microhyla carolinensis 2 0.42
Thamnophis sauritus 1 2.08
Thamnophis sirtalis 1 1.66
Tantilla coronata 1 0.62
Most reports on its food habits describe the beneficial aspects of
Cattle Egrets removing ticks from grazing animals, but Skead reports
that in South Africa the Cattle Egret only rarely removes engorged,
conspicuous ticks from cattle even when the ticks are abundant, and
no ticks were found in Lake Alice pellets. Besides a wide variety
of insects, Cattle Egrets eat arachnids (Solfuges et al.), centipedes,
frogs, toads, clawed toads (Xenopus spp.), lizards, and mice. There
is even one second-hand report of a Cattle Egret eating a bird (Zosterops
spp.) in South Africa (Whistler, 1949, Skead, 1956, and Witherby et al.,
Little Blue Heron
The principal feeding technique employed by Little Blue Herons was
the Wade or Walk Slowly, but they also used the Stand and Wait technique.
Little Blue Herons would frequently "freeze" while wading, they would
slowly lower the head and neck, then strike. Although a few individuals
fed far from water, especially late in the season, most Little Blue
Herons fed in water a few inches deep around the edges of ponds and on
the prairies. The Little Blue Heron did not feed in social groups as
often as the Snowy and Cattle Egrets did, but several individuals often
fed in the same general area.
Young Little Blue Herons readily regurgitated their last meal at
the least disturbance. The very young sometimes dropped the pellet into
the nest and later re-ate it. Older individuals, generally, spewed a
rather neat pellet over the edge of the nest, or, later, from their
perch on a limb. These pellets appeared to be composed of a wide
variety of food stuffs. A conspicuous feature was the frequency with
which relatively large prey items were eaten. A redfin pickerel of
12 cm. or more, or a bullfrog (Rana catesbeiana) with a snout-vent
length of 6 to 8 cm. frequently composed the entire pellet.
The contents of the 50 Little Blue Heron pellets was: amphibians
nearly 54 per cent by volume, fish 32.5 per cent, invertebrates 12 per
cent, and reptiles nearly 1 per cent (see Table 7 for detailed analysis).
Reptiles were represented by two snakes.
Crayfish and spiders were the only invertebrates that contributed
substantially to the total food. Most of the spiders, dystiscsids,
and orthopterans listed on the table were from 10 pellets collected on
June 10 and 13. These mid-June pellets were also unique in other ways
and are discussed later.
The golden topminnow was the most important fish prey; it comprised
nearly as much volume as the other eight fish species combined. The
very similar banded topminnow (Fundulus cingulatus) was second in
importance, and the least killifish was third. Although the least
killifish was slightly less important volumetrically, in the diet of
the Little Blue Heron young than was the banded topminnow, it was noted
10 times more often than was the banded topminnov. The other six
species of fish eaten each contributed from 1.0 to 2.6 per cent of the
total volume of food.
Large ranid tadpoles (Rana spp.) and adult bullfrogs were the two
most important prey in this sample of 50 pellets. Although the sample
included 27 ranid tadpoles, the four bullfrogs nearly equalled them in
volume and together they comprised 34.1 per cent of the diet. Leopard
frogs were about half as important, and the green treefrog (Hyla
cinerea) was fourth in importance. Small unidentified ranids and one
pig frog (Rana grylio) were next in importance. Six newts (Diemictylus
Table 7.--Analysis of Fifty Pellets Regurgitated by
Young Little Blue Herons
Number Per Cent of
Hirudinea 1 0.02
Astacidae 6 5.13
Palaemonetes spp. 3 0.10
Anisoptera (5 nymph) 15 0.91
Locustidae 11 0.53
Tettigoniidae 8 0.30
Gryllidae 10 0.08
Gryllotalpidae 1 0.12
Ephemeridae 2 0.12
Coleoptera (larvae) 4 0.34
Dystiscsdae 12 0.55
Belostomatidae 4 0.10
Hydrophilidae 1 0.02
Tabanidae 1 0.02
Arachnida 73 3.96
Diemictylus viridescens 6 1.18
unidentified tadpoles 2 0.18
Acris gryllus 2 O.18
Hyla spp. 2 0.59
Tyla cinerea 6 4.73
u-identified Rana spp. tadpoles 27 17.15
Rana spp. 17 2.60
Rana catesbeiana 4 16.95
Rana grylio 1 2.37
Rana pipiens 7 7.88
Seminatrix pygaea 1 0.69
Thamnophis sirtalis 1 0.08
Chaenobryttus gulosus 2 2.60
Enneacanthus obesus 2 0.99
Esox americanus 3 2.37
Fundulus chrysotus 50 14.78
Fundulus cingulatus 10 4.53
Gambusia affinis 28 1.58
Heterandria formosa 105 3.15
Jordanella floridae 8 0.99
Micropterus salmoides 7 1.38
virideacens) were found in pellets from three different nests. There-
fore, this supposedly noxious amphibian was of moderate but regular
occurrence in the diet of young Little Blue Herons at Lake Alice.
The pellets averaged 8.9 prey items and were composed of an
average of 3.0 invertebrates (including 1.5 spiders), 1.5 amphibians,
less than 0.1 reptiles, and 4.3 fish. The most important prey in
volume were: ranid tadpoles, bullfrogs, golden topminnows, leopard
frogs, crayfish, green treefrogs, banded topminnows, and spiders, in
that order. These eight forms comprised 75.1 per cent of the diet.
Three items stood out as being of prime importance: tadpoles, bull-
frogs, and golden topminnows.
Many additional pellets, at least 200, were studied in the heronry
but were not collected or preserved. These pellets verified the
material collected and added one very interesting observation. Late
in the season, from mid-June through July, when few young Little Blue
Heron, remain in the heronry, there was a major shift in their food.
Fish became much less important; tree frogs, spiders, and orthopterans
became predominate. The general trend was away from aquatic and toward
more terrestrial prey. Many adults fed in open grasslands and pastures
during mid-summer. Little Blue Herons wading through the grass and
"peering over" in their typical Wade or Walk Slowly technique were as
frequently seen as those wading in water.
Baynard (1912) analyzed the contents of 50 pellets regurgitated by
young Little Blue Herons at Orange Lake. They contained 1,900 grass-
hoppers, 37 small frogs, 149 cutworms, 8 lizards, and 142 small crayfish.
E. A. Chapin analyzed 46 Little Blue Heron stomachs (Howell, 1932)
and although the source of the birds was not stated the stomachs
were probably from several localities and probably collected throughout
the year. Crustaceans (principally crayfishes) composed 45 per cent
of the total food, small fishes (mainly minnows and killifishes with a
few catfishes and sunfishes) composed 27 per cent, insects composed
16.5 per cent and frogs, small snakes, and turtles made up 8.5 per cent.
Meanley (1955) analyzed 50 Little Blue Heron pellets which he
collected in Arkansas. He presented his data as frequency of occurrence.
A wide variety of insects, primarily aquatic forms, were eaten. Frogs,
especially leopard frogs, appear to have been quite important (found in
14 of 50 pellets). Crayfish vere very important (12 pellets). Fish
appear to have been less important, only a few species were taken:
Lepomis spp. (7 pellets), Esox spp. (2 pellets), and undetermined fish
During the breeding season Louisiana Herons usually fed by stealth,
both the Stand and Wait, and Wade or Walk Slowly techniques being used.
In addition to feeding in ponds and on the prairies, Louisiana Herons
were often seen standing immobile along the edges of canals and ditches.
When wading they often held the body parallel to the water, and the head
slightly retracted, and the neck shortened in an "a" curve. They
typically waded in deep water and often waded in water so deep that it
came up to their thighs, and sometimes to the belly.
The Louisiana Herons occasionally feed by employing some form of the
disturb and chase technique. A Louisiana Heron would run through shallow
water herding fish toward shore and trying to prevent their escape to
deep water by waving its wings. It sometimes hovered or flew low across
open water and reached down into the water with the bill to grab some-
thing as it flew by.
In the Gainesville area the Louisiana Heron is a solitary feeder.
Feeding individuals were widely scattered across the prairies and
many of them fed along streams and in ponds away from the prairie.
Young Louisiana Herons regurgitated their last meal much less
readily than did young of the other species at Lake Alice. When
disturbed, the older young readily moved out of the nest and climbed
up into the tree, but they often failed to regurgitate. Sometimes
they could be forced to regurgitate by shaking their tree, yelling,
banging on the limb and generally annoying them for 5 or 10 minutes,
but most of the time this too failed. When they did regurgitate they
did not usually produce a neat pellet, but typically scattered individual
fish about the ground beneath the tree. It was often impossible to
collect more than a few pellets from a brood throughout its whole nest
The 50 pellets were composed of fish, 95.4 per cent by volume,
various invertebrates, 4.2 per cent, and amphibians, 0.2 per cent (see
Table 8 for a detailed analysis). Only one frog, a cricket frog was
included in the 50 pellets. This one record shows how unimportant
amphibians were in the diet of young Louisiana Herons, and frogs are
here regarded as accidental.
The only invertebrates of importance in the over-all diet were
odonates. Of 58 invertebrates eaten 28 were dragon-flies and 8 were
damsel-flies (Zygoptera). Together they represented 3.2 per cent of the
total diet. One of the dragon-flies was a nymph and the other 27 were
adults. Because of their long membranous wings these insects were
Table 8.--Analysis of Fifty Pellets Regurgitated by
Young Louisiana Herons
Number Per Cent of
Palaemonetes spp. 2 0.23
Zygoptera 8 0.25
Anisoptera (nymph) 28 2.92
Tettigoniidae 4 0.20
Gryllidae 9 0.17
Belostomatidae 2 0.20
Hydrophilidae 1 0.03
Dystiscsdae 2 0.08
Diptera 1 0.03
Arachnida 1 0.08
Acris gryllus 1 0.17
C-aenobryttus gulosus 9 1.27
Elassoma spp. 30 0.79
Enneacanthus glorious 1 0.57
Enneacanthus obesus 1 0.42
Fundulus chrysotus 81 22.37
Fundulus cingulatus 19 7.93
Fundulus notti 8 1.13
Gambusia affinis 205 13.88
Heterandria formosa 143 4.53
Jordanellae floridae 210 36.82
Leptolucania ommata 1 0.08
Lucania goodei 4 0.11
Micropterus salmoides 5 1.98
Molliensa latipinna 11 2.83
Pomoxis nigromaculatus 4 0.91
conspicuous in the pellets. Their occurrence was sufficiently frequent
to preclude the assumption that they are taken rarely or by accident,
as is assumed for the other invertebrates. It would be interesting to
learn whether they were taken opportunistically or whether the birds
made a concerted effort to catch them. Their inclusion in the regular
diet may be of further significance in understanding the Louisiana
Heron's total ecology. The other 22 invertebrates showed wide variety
and altogether comprised 1.0 per cent of the food.
The flagfish was by far the most important prey species taken.
More individual flagfish, 210, were taken than any other species.
Golden topminnows were extremely important in the diet although only
81 of them were included as opposed to 205 individuals of third in
importance mosquitofish. The banded topminnow was fourth in importance,
and the least killifish was a relatively poor fifth in importance
although a total of 143 individuals were taken. Sailfin mollies
(Molliensa latipinna), fingerling largemouth bass (Micropterus salmoides),
warmouth (Chaenobryttus gulosus), and starhead topminnows (Fundulus
notti) composed from 2.8 to 1.1 per cent of the diet and were next in
importance. The remaining seven fish species each contributed less
than 1 per cent to the diet and involved from one to four individuals
each except for 30 individual pygmy sunfish (Elassoma spp.).
The pellets averaged 15.8 food items: amphibians less than 0.1,
invertebrates 1.1, and fish 14.6 individuals. The three most important
prey species, flagfish, golden topminnow, and mosquitofish, comprised
73.1 per cent of the diet.
Young Louisiana Herons regurgitated so infrequently that probably
no more than another 50 pellets were seen but not collected in the
heronry. These observations generally substantiate what is written
above, and none of these other pellets contained frogs.
Baynard (1912) analyzed 50 pellets regurgitated by young Louisiana
Herons at Orange Lake and found 2,876 grasshoppers, 8 small frogs,
17 cutworms, 6 lizards, and 67 small crawfish. These results are
inconsistent with my finding at Lake Alice and cannot be explained.
The findings of E. A. Chapin (Howell, 1932) who analyzed 48 Louisiana
Heron stomachs, were more consistent with my data. Although not
stated the stomachs he analyzed were probably collected at all seasons
throughout their range: killifish composed 68 per cent of the total
food in these stomachs, crustaceans (mainly prawns and a few crawfish)
composed 20 per cent, and the balance included clam worms, spiders,
weevils, grasshoppers, giant water bugs, dragon flies, water beetles,
and ground beetles.
COMPARISON OF REPRODUCTIVE HABITS OF THE SPECIES
The breeding histories of Snowy Egrets, Cattle Egrets, Little Blue
Herons, and Louisiana Herons are quite similar, but there are differences
in the details and these vary from the most trivial to some of real
ecological significance. Some of these differences amongst species are
the direct result of their interspecific relationships within the
heronry during the breeding season, and others are the result of differ-
ences in the total biology of the species. Unfortunately there are
practically no qualitative studies on any phase of the biology of these
birds with which the data from Lake Alice can be related. In this
chapter, the breeding of each of the four most abundant species at
Lake Alice will be compared.
In 1958, the various species of herons appeared to be selecting
slightly different nest sites. The result of these differences was a
vertical stratification of the nests. In 1958, Snowy Egrets nested at
lower and more exposed sites than did the other species. Most of their
nests were between three and five feet above the heronry floor, with
a few up to a maximum of about ten feet. The birds built their nests
around the edge of the heronry and around openings in the vegetation
throughout the middle of the heronry. Little Blue Herons built their
nests higher than did Snowy Egrets, mostly around ten feet and occasionally
still higher. Little Blue Heron nests were always built in better
sheltered, sturdier appearing locations than were the Snowy Egret nests.
Many Little Blue Heron nests were built against the main trunk of the
nest tree. The Louisiana Heron nested at heights of 2 to 5 feet, much
lower than any of the other species, but in contrast to the Snowy
Egret, the Louisiana Heron nests were always in well sheltered places.
Cattle Egrets started nesting in the middle of the heronry in the
denser vegetation of the larger maples. Their nests were usually from
4 to 8 feet above the heronry floor in a variety of sites. Later in
the season as the heronry spread, Cattle Egrets started nesting around
the edge and openings of the new heronry as well as in the middle. It
appeared that Cattle Egrets were selecting about the same type of nest
sites as the Snowy Egrets did earlier in the season and that they
differed from the Snowy Egret sites only in being slightly higher. The
net result of this stratification was a reduction of interspecific
In 1959, there did not appear to be any really systematic stratifi-
cation of nests at Lake Alice. Most Louisiana Herons nested low in the
bushes and some Cattle Egrets appeared to nest higher than did any of
the other species. For the most part there appeared to be so much overlap,
so many birds nesting from four to six feet above the heronry floor, that
there was little effective separation of the species.
In 1960, more detailed observations were made. The heights of all
nests in the study area and the species of all nest trees or bushes were
recorded. The heights of the nests revealed some interesting features.
Snowy Egrets and Louisiana Heron nests were consistently the lowest;
nests of both these species averaged 5.7 feet above the water or ground.
Cattle Egrets nested substantially higher and their nests averaged 7.8
feet above the heronry floor. The Little Blue Herons nested at an
average height of 7.2 feet throughout the season. The difference in
nest height between Cattle Egrets and Little Blue Herons was signifi-
cant ("t" 2.08). As pointed out earlier there was a substantial
difference in clutch size between early and late nesting Little Blue
Herons. The Little Blue Herons that completed egg-laying by April 28
built their nests at an average height of 6.7 feet, but those that
completed their clutches after April 28 nested at an average height of
8.5 feet. There was an obvious trend for the earliest breeding herons,
regardless of species, to establish territories which included the
lowest nest sites. These low sites tend to be sturdier than the high
sites. The situation was somewhat confused by Little Blue Herons,
because even the early nesting pairs selected slightly higher sites
than did the contemporaneous Snowy Egrets and Louisiana Herons. How-
ever, the primary factor causing the stratification appears to have
been the differences in the time of nesting. The general trend being
for the earliest nesting pairs to build their nests in the lowest,
and probably sturdiest sites available and for later nesting individuals
to build their nests higher.
In 1960, the heron nests at Lake Alice were built only in shrubs
or trees. The birds built their nests in red maple, buttonbush, elder,
myrtle, or willow. Red maple was the most important nest site; 37.5
per cent of all heron nests were placed in red maple. Buttonbush was
very important and held 28.4 per cent of all nests. Elder with 19.8
per cent of the nests is third in importance. Myrtle and willow with
8.2 and 6.0 per cent are considerably less important to the heronry as
A summary of the herons' nesting substrate is presented in Table 9.
It is interesting that red maple is the most frequent nest site of all
species except the Louisiana Heron. Buttonbush is the second most
frequent choice of all the species. Louisiana Herons use elder more
frequently than they use any other bush or tree and they use it much
more frequently than do the other herons. The two tree species most
frequently used for nesting by each heron species hold about two-thirds
of the nests of that species, except for the Little Blue Heron. The
Little Blue Heron shows stronger nest site preference than do the three
other herons and builds 85 per cent of its nests in maple and buttonbush.
The four heron species do show differences in their nest site.
There are three average nest heights: 5.7, 7.2, or less, and 7.8 feet.
These effectively divided the four species into three groups. The two
species that nest at lower elevations use different trees for nesting.
One of them, the Louisiana Heron, uses elder most frequently and button-
bush next most often and builds many nests in myrtle. The other, the
Snowy Egret, uses maple, buttonbush, and elder in that order, and only
occasionally builds in-myrtle and willow. Thus, although they both
nest rather early, these species tend to have reduced interspecific
competition because of the differences in nesting substrate. The Little
Blue Heron builds its nests higher than these two species do, and the
Cattle Egret builds its nest the highest of any of the herons.
Table 9.--The Species of Trees and Bushes Used by Four
Species of Herons For Nest Building at Lake Alice, 1960
Little Blue Heron
Per Cent of Nests in
Each Type of Tree
In all four species the females build the nest with twigs and sticks
that are brought to them singly by the males. Male Little Blue Herons
and Cattle Egrets gather their twigs from bushes and trees near the nest
site. The Little Blue Heron tends to hunt for twigs at all levels in
the bushes and trees while the Cattle Egret tends to limit its collect-
ing to the upper and outer reaches of trees and bushes. In general
the Cattle Egret gathers smaller twigs than do the other species. Male
Snowy Egrets gather all their twigs from the ground or from the water
beneath the heronry. Some Snowy Egret nests, especially early ones,
are built entirely of sticks that have lain beneath the heronry for a
year or more and are weathered smooth and often covered with mud. But
females of all species frequently drop twigs which they are attempting
to work into the nest, and incomplete nests especially, and a few com-
plete ones too, may be dismantled and the twigs scattered on the heronry
floor. These twigs, including ones broken off by male Little Blue
Herons and Cattle Egrets, are found and picked up by the male Snowy
Egrets. The Louisiana Heron picks up twigs from the heronry floor in
the manner of the Snowy Egret, but it also breaks twigs off low bushes
and large fallen limbs. In all species there is a brief twig passing
ceremony which generally involves elevating certain feathers, especially
those of the crown. All species but the Cattle Egret spend an average
of four to five days building the nest before the first egg is laid,
at which time the nest is typically incomplete. The nest is completed
during the egg laying period. Cattle Egrets spend an average of between
six and seven days building the nest before they lay their first egg, or
an average of about two days longer than the other herons. Most Cattle
Table lO.--Nesting Statistics of Four Species
of Herons at Lake Alice
Days to build nest
Days between laying
Number eggs laid
Number eggs in clutch
(4 or 5)
(days) 22.4 23.8 22.8 22.9
Number eggs day before
hatching 3.8 4.1 3.7 3.5
Number hatching 3.3 3.7 3.2 3.1
Egret nests are complete when the first egg is laid or are at least more
nearly complete than are nests of the other species.
E Layi and Clutch Size
Most eggs were laid at two-day intervals, that is, the eggs were
laid on alternate days. There were no intervals of more than two days.
All Cattle Egret eggs were laid at two-day intervals. But occasionally
Snowy Egrets, and even more frequently, Little Blue Herons and Louisiana
Herons (see Table 10) laid eggs on consecutive days. Typically there
was never more than one one-day interval per nest; exceptions tended
to be limited to larger clutches.
Snowy Egrets, Louisiana Herons, and Little Blue Herons lost an
average of 0.2 of an egg per nest between laying and completion of the
clutch. Losses of eggs and their passage through the bottom of incom-
plete nests account for most of this loss. However, Cattle Egrets lost
no eggs between laying and completion of the clutch. In spite of these
early losses by the other species, the Cattle Egret still had the
smallest clutch, and the differences in clutch size were sufficiently
great that there must obviously be other differences in the life histories
of these species.
Although their clutches were the smallest, Cattle Egrets did not
have significantly smaller clutches than Little Blue Herons ("t" = 1.18).
Neither did Snowy Egrets have significantly smaller clutches than
Louisiana Herons ("t" 1.65). All other differences in clutch size
were significant, for example, the differences between Little Blue Heron
and Snowy Egret clutches had a "t" of 3.46.
Although no intentional experiments were performed, the daily
removal of eggs from some nests by predators and other egg losses lead
to the conclusion that all four of these herons are indeterminate layers,
but that the maximal number of eggs they can lay serially is about
double the average clutch size for the species.
The incubation periods of these herons are quite similar (see
Table 10). The Snowy Egret has the shortest average incubation period,
the Little Blue Heron and Cattle Egret require an average of about half
a day longer. The Louisiana Heron requires one and a half more days
for incubation than did the Snowy Egret, and a day more than do the
two species with the intermediate incubation period. Because Louisiana
Herons have the largest clutches, nest first when temperatures are
still low, and do less late nesting than the other species, it could be
reasoned that their longer incubation period is a result of the birds'
inability to keep more eggs during cooler weather as warm as the other
species do less eggs in warmer weather. However, there is no evidence
to substantiate these ideas and no correlations between early and late,
or small and large clutches could be made.
In all four species both sexes incubate. The adults stand over the
eggs and shade them during mid-day in late spring and summer. Cattle
Egrets shade their eggs more than the other species and in this case
the difference is doubtless related to the later nesting of the Cattle
Hatching and the Young
Young herons of all four species often call inside the egg before
they pip. The eggs are usually pipped one day or slightly less, rarely
two days, before the young emerge. The adults (of all species) remove
the empty shells after each young hatches, and drop the shells over the
edge of the nests. About the time the first egg is pipped the adults
also remove any cracked or empty eggs even though they may have incu-
bated them for the full period.
On the first day of hatching Louisiana Heron broods average 2.2
young; most of their broods are complete by the third or fourth day of
hatching. Snowy Egret and Little Blue Heron broods average 1.5 and
1.6 young respectively on the first day of hatching, and most of their
broods are complete by the third or fourth day of hatching. Cattle
Egret broods average 1.1 young on the first day of hatching and most
of their broods are not complete until the fifth day of hatching.
The average number of young hatching per nest is closely related to
the number of eggs per clutch (see Table 10). Most Snowy Egret, Little
Blue Heron, and Louisiana Heron hatchlings are brooded almost continu-
ously during their first few days of nest life, but when they are able
to hold their heads upright and strike at objects, the two parents
simultaneously vacate the nest. Cattle Egrets spend considerable time
shading the young, but individual young Cattle Egrets probably do not
receive as much parental brooding and shading as do nestlings of the
other herons. Cattle Egrets hatch over such a long period of time that
both parents are off gathering food for the older nestling while the
youngest are still so undeveloped that they would be continually attended
if they were by themselves. The newly hatched young probably passively
receive many of the benefits of brooding from their older siblings.
Also, since Cattle Egrets nest substantially later than the other
species do, there is considerably less danger that the young might
become chilled during the day.
The young dry off shortly after hatching. They are relatively
helpless and remain in the nest for some time and have down growing
only on the future pterylae. At first they are extremely weak and
seldom peep or raise their heads but after two or three days they
peep more and hold up their heads for relatively long periods. Although
at first they pick food up from the nest floor they soon take it
directly from the parent's bill and shortly reach down into the parent's
gullet for the food.
There is no evidence that any of these birds raise two broods in
one season although the over-all breeding season is sufficiently long
for this to be done.
Mortality of Eggs and Young
Even before the first egg is laid various factors which increase
mortality begin to operate. Wind often blows down nests that are just
being started, in most cases this is probably due at least in part to the
adults trying to build the nest at an impossible site. Other herons may
try removing twigs from a temporarily unprotected nest, and if the nest
is just started it usually falls to the ground. Even sturdy nests can
seldom survive the removal of more than two or three twigs. These
delays in nest completion often result in the bird's laying the first
egg before the nest is complete enough to hold the egg.
The Cattle Egret spends considerably more time building its nests
than do the other herons, and its nests are much more complete before
they start laying. The Cattle Egret loses practically no eggs between
laying and incubation while the other species lose between 3.9 and 5.4
per cent of their eggs (see Table 11). Not only are Cattle Egret nests
more complete but the adults are more attentive, and incubation starts
with the laying of the second egg.
Sometimes the birds never succeed in their efforts to build a nest.
One nest that never reached completion was started on April 20, 1960;
it was there the 21st, but completely gone the next day; on April 26
a nest was started at the same place, the next day it was a large nest,
but a day later only a few twigs remained, and on April 30 there was
no evidence of the nest; on May 3 it was started, but on May 5 it was
gone; on May 7 it was started again, and on May 9 it was gone again.
In 19 days this nest was started four times, and each time it lasted for
at least two days, and it disappeared four times. This particular nest-
ing effort was the work of a pair of Little Blue Herons. There was no
activity at the site for the next month and a half, but in late June a
pair of Cattle Egrets built a nest at the same site. They laid and
hatched five eggs with no apparent difficulty.
Grackles or other predators may find a heron's nest and remove the
eggs as regularly as they are laid. One Snewy Egret nest that was
regularly robbed never did produce young. This particular nest was
started on April 5, 1960. The first egg was found on the 11th and on
the 13th there were two eggs. On the 14th there was only one egg, a new
one, and the next day there were none; on April 17th the fourth egg was
laid, and the next day it was gone and the nest again empty; on April 19
one egg was added, but it was removed by the next day. Then the clutch
was completed; eggs being laid on the 21st, 23rd, and 5th of April,
and incubation proceeded for nine days. On the 5th of June egg number
two disappeared. On the 7th number one was gone, and on the 8th
number three was gone. On the 9th the nest was reduced to a few twigs
scattered beneath the tree. Most of these eggshells were recovered.
They had been opened and eaten by birds, apparently Boat-tailed
Grackles (Cassidix mexicanus).
Purple Gallinules (Porphyrula martinica) also take eggs from
nests. Young Purple Gallinules feed on eggs brought to them by the
adult birds. A few eggs that had been crushed inwardly until the outer
shell was a cluster of tiny fragments held together by the membrane were
found at widely scattered locations. They had apparently been taken
and eaten by Rat Snakes (Elaphe obsoleta), the only arboreal snake seen
in the heronry.
Fish crows (Corvus ossifragus) are common on the University campus
adjoining Lake Alice. They often perched in trees around the lake, and
nearly every day of the 1960 breeding season they were seen flying over
the heronry. It is interesting that these fish crows were never seen in
the heronry proper, and there was no mortality either of eggs or young
that could be attributed to these birds. There was no evidence of any
mamalian predation. In fact there was never any evidence of manuals
other than mice having been in the heronry. Raccoons (Procyon lotor)
and other potential mamalian predators are doubtless incompatible with
the American alligator (Alligator mississipiensis) which is numerous
at Lake Alice.
Alligators from one foot to six feet long and occasionally larger
individuals scavenge in the heronry. These animals promptly eat dead
nestlings, regurgitated fish and frogs and anything else remotely edible
that fallP to the heronry floor. In performing this scavenger service
they keep the heronry largely free of the biological wastes that would
have attracted Fish Crows, raccoons, or other potential predators.
A great many nests are blown down, destroyed, robbed, or deserted
during construction, egg-laying and early incubation. Probably well in
excess of half of the nests started never reach the point of containing
a full clutch. Once the clutch is complete and incubation gets under
way, the eggs are relatively safe. But even then predators manage to
get a few nests, and when they do they generally take all the eggs,
often removing them one at a time over a period of several days.
From the day before hatching starts through hatching there is a
mortality of from 10 to 15 per cent (see Table 11). There is some
loss of young to predators at this time. The adults are restless and
they accidentally crush an occasional egg or young while moving around
on the nest. Unaccountably the Snowy Egret nests suffered the highest
hatching mortality. The over-all mortality from egg laying through
hatching ranged from a low of 12.6 per cent for the Cattle Egret through
a high of 19.3 per cent for the Snowy Egret. The Cattle Egret, Little
Blue Heron, and Louisiana Heron had similar mortalities at hatching
but the Cattle Egret's lack of loss in the egg laying period did much
to suppress its over-all mortality.
Cattle Egrets lose practically no nestlings during the first two
weeks after hatching. The Cattle Egret mortality of 5.7 per cent of its
nestlings represents a loss of about one young from every five nests.
Snowy Egrets, Little Blue Herons and Louisiana Herons have a nestling
mortality of from 25.4 to 32.6 per cent during the first two weeks.
Most of this loss is due to starvation. The last sibling to hatch in
practically all the larger clutches of these three species is usually
so far behind his older siblings that he seldom gets enough food to
survive for more than a few days. Only occasionally did more than one
young starve in a nest. This loss averages about one young per nest,
however young were seldom starved in broods as small as two. The Snowy
Egret had the highest nestling mortality, while the Little Blue Heron
and Louisiana Heron had very similar mortalities.
The over-all mortality of eggs and young from nests in which young
eventually hatch varies from a remarkably low 17.5 per cent for the
Cattle Egret to a surprisingly high 45.6 per cent for Just the period
from egg laying through the first two weeks of nest life (Table 11).
There is another period of rather high mortality when the young
first leave the nest and start climbing about in the trees. Young
often fall to the ground. At Lake Alice the vegetation is sufficiently
bushy for these young usually to climb back to their nests, but at
other places where herons nest in large mature trees, the inability
of young that fall from nests to get back into the trees is an important
factor in mortality. At Lake Alice a few young are caught by alligators
before they get back in their tree, and Sprunt and Chamberlain (1949)
report recovering bands from young Louisiana and Little Blue Herons from
an alligator stomach. Strong winds and heavy rains result in losses;
young are knocked from trees and are hung in vegetation or have their
feathers matted with mud and pounded into the mud.
Table 11.--Mortality of Eggs and Nestlings of
Four Herons, Lake Alice, 1960
Mortality in Per Cent
Snowy Cattle Little Blue Louisiana
Egret Egret Heron Heron
Laying to day before
hatching 5.4 0.0 3.9 3.9
Day before through
hatching 14.7 12.6 12.1 10.5
hatching 19.3 12.6 15.6 14.0
two weeks 32.6 5.7 26.2 25.4
from laying through
two weeks 45.6 17.5 37.6 35.8
Cattle Egret broods averaged 2.9 at the end of two weeks of nest
life. Louisiana Herons averaged 2.8 young, Snowy Egrets averaged
2.6, and Little Blue Herons averaged 2.4. Although these Cattle Egret
broods were not significantly larger than Louisiana Heron broods
("t" : 0.97), the Louisiana Heron clutches contained significantly
more eggs than Cattle Egret clutches ("t" : 4.29). The Cattle Egret
has such a low nesting mortality that in spite of its laying fewer
eggs than the three other herons, it produces more young.