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The comparative biology of two species of swifts in Trinidad, W. I

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Title:
The comparative biology of two species of swifts in Trinidad, W. I
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Collins, Charles Thompson, 1938-
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English
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vi, 103 leaves. : illus. ; 28 cm.

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Animal nesting ( jstor )
Bird nesting ( jstor )
Birds ( jstor )
Breeding ( jstor )
Eggs ( jstor )
Feathers ( jstor )
Hatching ( jstor )
Nesting sites ( jstor )
Species ( jstor )
Swifts ( jstor )
Dissertations, Academic -- Zoology -- UF
Swifts ( lcsh )
Zoology thesis Ph. D
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bibliography ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis -- University of Florida.
Bibliography:
Bibliography: leaves 95-102.
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Manuscript copy.
General Note:
Vita.

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THE COMPARATIVE BIOLOGY OF TWO SPECIES OF SWIFTS IN

TRINIDAD, W. I.











By
CHARLES THOMPSON COLLINS













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













UNIVERSITY OF FLORIDA

June, 1966













ACKNOWLEDGMENTS


I extend my deep appreciation to Pierce Brodkorb for his valuable supervision of this problem. Sincere thanks are also due to the other biologists who critically read the manuscript: E. G. Franz Sauer, Thomas J. Walker, Brian K. McNab, and Frank G. Nordlie. I am particularly grateful to David W.

Snow for acquainting me with these swifts and their nest sites and for making his notes available to me. Miss Jocelyn Crane and the Department of Tropical Research of the New York Zoological Society greatly facilitated my field work in Trinidad. Thanks are also due Mrs. H. Newcomb Wright, Spring Hill Estate, Arima Valley, Trinidad, for her hospitality and permission to study the swifts nesting there. I wish to gratefully acknowledge the financial support for this study received from the Frank M. Chapman Memorial Fund of the American Museum of Natural History in 1962 and 1963, and in 1964 the National Science Foundation (Summer Fellowship for Graduate Teaching Assistants) and Cyril K. Collins.

To John Beckner who identified the nest materials, and

to John F. Anderson, Frank M. Mead, Thomas E. Snyder, Phyllis T. Johnson, and Robert E. Woodruff, who identified the arthropods, I am also grateful.







ii

















TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS .................... . ii

LIST OF TABLES . . . . . . ..... v

LIST OF ILLUSTRATIONS .. .. . ... . ....... . vi

INTRODUCTION ...... . . .. ... ....... . 1

STUDY AREA ................ ...... ..... 3

METHODS AND MATERIALS . . . . . . . . . 5

GENERAL DESCRIPTION. . . ... ... . .... 8

RANGE. . .. . ..... ... . .. . 10

NESTS AND NEST SITES . . . . . . . . . . 11

Chaetura brachyura . . . . . . . 11
Cypseloides rutilus . .. . . . . . . 18

BREEDING SEASONS . . ............... . .. . . . 27

CLUTCH SIZE . . . . . . . . . . . . 33

INCUBATION . . . . . . . . ... .... . 38

PARENTAL CARE . . . . . . . . . . . 41

Chaetura brachyura. .. . .............. 41
Nestling period. ... ... .......... 41
Fledgling period . . . . . .... . 41
Cypseloides rutilus ..... .. ... ...... . 42

BROODING . . . . . .* .. . . . ... 44

FLEDGING SUCCESS . .. . .. . . . . . . 45

GROWTH .. . ................ ... ... 47

Body weight ................... 47

iii










General development ....... .......... 53
Feathers . . . .. . . . . . 53
Eyes ... . . . ...... . .... 58
Bill and feet. ..... . . . . . . 58
Behavior .......... . . . . .... 61
Development of homeothermy. ............ .. 62
Torpor . . . . . . . . . . 66

ADULT WEIGHT . . . ... ... . . ... 68

FOOD AND FEEDING HABITS. ... .... . .... . ... 70

FEEDING OF YOUNG .. . . . . . . .. .. . 81

MOLT . . . .. ..... ....... ....... 84

PARASITES AND PREDATORS. ........... .... . 85

DISCUSSION ......... . . . . ..... . 87

SUMMARY ...... . ..... . ..... . . . 93

LITERATURE CITED . . . . . . ........ . 95

BIOGRAPHICAL SKETCH. ........ . . . .. . 103


































iv
















LIST OF TABLES

Table Page

1. Nest dimensions of swifts of the genus Chaetura. 16

2. Distribution of Chaetura brachyura nests in halfmonth intervals. . ... . . . . .. 30

3. Distribution of Cypseloides rutilus nests in halfmonth intervals. ... . ......... . . 31

4. Distribution of clutch sizes of Chaetura brachyura by half-month intervals for years 1962 to 1964 . 34 5. Clutch size of swift species in the genus Chaetura 35

6. Average hatching and fledging success of swift species .......... .... ..... . . .. 39

7. Daily weight (grams) and relative growth rate (per cent) of Chaetura brachyura ...... . 50

8. Daily weight (grams) and relative growth rate (per cent) of Cypseloides rutilus ....... . . 51

9. Average daily growth rate (grams) and relative growth rate (per cent) for five-day intervals for
Chaetura brachyura and Cypseloides rutilus . . 52 10. Contents of food balls collected from nestlings
of Chaetura brachyura and Cypseloides rutilus. . 75
















v













LIST OF ILLUSTRATIONS

Figure Page

1. Cold chamber used in tests of thermoregulatory
capacity of nestling swifts. .... . . 7

2. Manhole nest sites of Chaetura brachyura . . 13 3. Nests of Chaetura brachyura. . . . . 15

4. Nests of Cypseloides rutilus . . . . . 20

5. Nesting material of Cypseloides rutilus growing
on stream-side rock ledge. . . . . . 22

6. Stream nesting habitat of Cypseloides rutilus. . 24 7. Growth curve of Chaetura brachyura . . . . 48 8. Growth curve of Cypseloides rutilus. . . .. 49

9. Growth of the wing of Chaetura brachyura and
Cypseloides rutilus . . . . . . 55

10. Growth of the tail of Chaetura brachyura and Cypseloides rutilus. .. .. .. .... 56

11. Chaetura brachyura nestlings and fledglings. . 60 12. Body temperatures of nestlings of Chaetura brachyura when unbrooded ..... .. . . . 63

13. Body temperatures of nestlings of Cypseloides rutilus when unbrooded . . ............ 64

14. Decrease in body temperature of nestling swifts under cold stress. ... .. . . 65

15. Size of prey selected by Chaetura brachyura and Cypseloides rutilus . . . . . . . 79










vi















INTRODUCTION


Swifts of the family Apodidae form a well-defined group of streamlined, fast-flying birds which spend most of the daylight hours on the wing in pursuit of their insect prey. They occur throughout the world but are most abundant in tropical regions. Although the biology of swifts has been studied in Africa (Moreau, 1941, 1942a, 1942b), South America (Sick, 1948a, 1948b, 1959) and Malaysia (Medway, 1962a, 1962b), the family as a whole is still poorly known. The nests of several species have only recently been discovered (Rowley and Orr, 1962) and others are undescribed. A new species remained undetected in a well studied part of northwestern South America as late as 1962 (Eisenmann and Lehmann, 1962). The difficulty of locating swift nests, which are usually solitary and often in inaccessible cliff crevasses or in hollow trees, has clearly hindered the study of additional species, particularly in the tropics. At present, detailed life history data are confined for the most part to a few species of the temperate zone (Lack and Lack, 1951, 1952; Weitnauer, 1947; Fischer, 1958).

The island of Trinidad, having probably the largest

swift fauna for an area its size, offers abundant opportunities for ecological studies. The preliminary work by Snow (1962) indicated the practicality of a detailed comparison of two of the

1






2


nine species of Trinidadian swifts. These two species, the short-tailed swift, Chaetura brachyura (Jardine), and the chestnut-collared swift, Cypseloides rutilus (Vieillot), are approximately the same size but have striking differences in nesting ecology, clutch size, and the development of the young. The present study was undertaken, therefore, to analyze these differences and, when possible, to point out their adaptive significance.

Differences in nest type have been shown to be useful

characters in differentiating species of swiftlets of the genus Collocalia (Sims, 1961; Medway, 1961), while differences in ecology and clutch size appear to be significant indicators of higher intrafamilial relationships (Lack, 1956a). Thus the study of the comparative ecology of additional species, in conjunction with studies of the anatomy, osteology, and paleontology of swifts, should provide knowledge useful in understanding the evolution of the Apodidae.
















STUDY AREA


The William Beebe Tropical Research Station of the

New York Zoological Society in Arima Valley, Trinidad, formed the base of operations for this study. The station, located four miles north of the town of Arima, is at an elevation of 800 feet and provides an excellent vantage point from which to observe feeding swifts, as well as being close to nesting concentrations of both species. The present study included approximately eleven months of field work in Trinidad during part or all of the breeding seasons of 1962-1964, exact dates being 26 June-1 Sept. 1962; 25 April-11 July 1963; 8 May-11 Nov. 1964.

The ecology of Arima Valley has been described in some detail by Beebe (1952), and the best description of the vegetation types in Trinidad is that by Beard (1946).

Field observations were concentrated in the eastern half of St. George County and included areas of low country savanna, upper montane rain forest at elevations of 2500 to 3000 feet, and the rocky coastline of the north shore of the island. The principal nesting area for C. brachyura was Waller Field, a United States Air Force base deserted for more than ten years and heavily overgrown except for the roads and a few cement structures. Most nests of C. rutilus were located in

3







4


the northern half of Arima Valley, but a few were in sea caves on the north coast, particularly near the town of Blanchisseuse.
















METHODS AND MATERIALS


During the nesting season individual nests were checked regularly, usually once a day or less in order to avoid excessive disturbance and possible desertion.

In 1962 adults and nestlings were marked with numbered, colored plastic bands and, starting in 1963, also with U. S. Fish and Wildlife Service numbered, aluminum bands. Nestlings less than 8-10 days old could not be banded and were marked with spots of color applied with a felt marking pen to the skin of the back or belly. Color marking of nestlings and adults was only used to a limited extent. An attempt to color mark a prebreeding flock of C. brachyura, by painting the primaries of one wing yellow, proved unsuccessful as the birds could not be readily distinguished in the field.

Weights of adults and nestlings were obtained with

spring balance of the type obtainable from the British Trust

for Ornithology. This balance was calibrated in half-gram intervals, and weights were estimated to the nearest quarter gram.

Environmental temperatures were obtained by means of Six's type maximum-minimum recording thermometers. Body temperatures were measured with a small bulb mercury thermometer made by the Schultheis Corporation. Readings were

5






6


taken with the bulb inserted about 10 mm into the cloaca.

Cold stress experiments were used as a part of the investigation of nestling thermoregulation. These involved a 6x8x5 inch cold chamber constructed of 1-1/8 inch thick foam plastic insulation material (Fig. 1). When equipped with four 6-oz cans of "Skotch Ice" (refreezable liquid), this chamber maintained a temperature of approximately 5 C for several hours. In the field, nestlings were placed individually in the chamber for a period of 5 minutes, and their temperatures were recorded before and after cold exposure. Even though sharp body temperature drops were recorded for very young nestlings, no ill effects were attributable to this test.

Swifts of both species were captured at night roosting places for weight and molt studies. Flocks of C. brachyura were generally confined in a roost site and examined the following morning. A hand net was used to capture C. rutilus adults roosting in a river gorge in Arima Valley; they were held in captivity over night and released the following morning.

























































Fig. 1. Cold chamber used in tests of thermoregulatory
capacity of nesting swifts.
















GENERAL DESCRIPTION


Chaetura brachyura is one of four similar-appearing

congeneric species that occur in Trinidad. It is a small bird about 115 mm long with a short stubby tail (28-33 mm) and long narrow wings (117-127 mm). In fresh plumage it is dark blackbrown, except for the rump and under tail coverts which are pale ashy brown. The throat is slightly paler than the breast. The feathers of the darker areas, particularly the remiges, have a noticeable greenish gloss or iridescence. In worn plumage the gloss is purple or completely bleached out to a lusterless dark brown, and the bird appears paler, particularly on the throat, and is more brownish than black. Occasional individuals have been collected in late summer with extremely light brown underparts, but the cause of this is not understood. Birds in juvenal plumage are less glossy on the body areas than adults and have a more grayish tinge to the paler rump and under tail areas.

Cypseloides rutilus appears to be a larger swift

(135 mm) owing to its longer tail (38-42 mm), but its wings are about the same length (119-128 mm) as those of C. brachyura. In over all color C. rutilus is dark sooty black-brown, darker on the wings and tail than on the body. The males have a complete collar of rufous feathers covering the nape, auricular,

8






9


loral and malar regions, but not the interramal areas nor the throat and upper portion of the breast. The females are generally uniform dark brown. A few birds have a partial rufous collar on the nape and extending laterally to the edges of the throat, with sometimes additional flecks on the throat and breast. Two such birds were collected and both proved to be females. Despite numerous statements to the contrary it is not the juveniles that completely lack the collar. In fact, birds in juvenal plumage invariably have some rufous present as a partial collar. The edges of the collar are not so sharply delimited as in the adults, and the crown feathers also have narrow reddish edges. The extent of the rufous coloring in the juvenal plumage is variable, but it is never so extensive as in adult males nor is it completely lacking as in most adult females.
















RANGE


Chaetura brachyura inhabits the southernmost Lesser

Antilles and northern South America, with a single report in southern Panama. It is abundant on the islands of St. Vincent, Trinidad, and Tobago and on the mainland from Venezuela and Colombia south to Peru and the Matto Grosso of Brazil.

Cypseloides rutilus ranges continuously from southern Mexico to Peru and Bolivia and east through northern Venezuela and Trinidad. A separate population also exists in the highlands of southeastern Venezuela and the neighboring parts of

British Guiana.



























10















NESTS AND NEST SITES


Chaetura brachyura

There are relatively few records for nests in natural settings for most species of Chaetura. The available information indicates that all tend to utilize hollow trees or stumps and occasionally affix their bracket-shaped nests to vertical rocky ledges or the walls of caves (Lack, 1956a). Most species in the genus have been quick to accept various artificial equivalents of these natural hollows, and as early as the 1870's accounts began to appear in journals of their nesting in numerous man-made structures including chimneys, wells, cisterns, and a variety of buildings (Lack, 1956a; Fischer, 1958). The species most clearly illustrating this habit is the North American chimney swift, Chaetura pelagica (Linnaeus), which "now breeds much more often in chimneys than in trees" (Lack, 1956a). Other New World species of Chaetura known to use manmade structures are C. vauxi vauxi (Townsend) in temperate areas (Baldwin and Hunter, 1963; Baldwin and Zaczkowski, 1963) and C. vauxi aphanes Wetmore and Phelps, Jr. (Sutton, 1948), C. andrei Berlepsch and Hartert (Sick, 1959) and C. brachyura (Haverschmidt, 1958) in tropical South America. In Trinidad C. brachyura has previously been reported to use chimney and sea-cave nest sites (Belcher and Smooker, 1936), as well as 11






12


subterranean manholes and a nest box erected for swifts (Snow, 1962).

The C. brachyura nest sites followed in this study were all in vertical manholes which were part of the underground drainage system of Waller Field (Fig. 2). Eleven of these sites were discovered by Snow and kept under observation by him from May 1957 until September 1961 (Snow, 1962). An additional ten holes used as nest or roosting sites were found during this study and observed during 1962-1964. For the most part the manholes were cylindrical concrete tubes from 4-20 feet deep, connecting with a smaller lateral drainage pipe at the bottom. The holes had an inside diameter of about 4-1/2 feet, and usually had a concrete top pierced by a circular access hole, 2 feet in diameter, which at one time had been closed by a metal manhole cover. One hole, slightly narrower and made of bricks, had an uneven surface as opposed to the smooth walls of those made of concrete. The only site not in one of these holes was located in a subterranean, concrete-walled room about 20 feet long, 10 feet wide, and 10 feet high. The swifts entered and left this room through a 12-inch square opening in the ceiling, which was flush with the ground level. The tops of several of the manholes were also flush with the ground; others protruded as much as 4 feet above ground. One of the manholes used predominantly as a roosting site was nearly roofed over with a metal sheet covered by cement, with only a very small hole, 5-1/2 by 10 inches, providing access for the swifts. Fourteen of the 21 sites were partially filled with






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Fig. 2. Manhole nest sites of Chaetura brachyura, Waller Field, Trinidad.






14


water or had water flowing through the bottom drainage pipe during the nesting season. In three sites nests were destroyed, and in one case an adult was trapped by rising water in the hole. Although the nest sites were usually brightly illuminated there was very little circulation of air, and the relative

humidity was in excess of 95 per cent at all times. The temperature in these manholes had a range of from 25.0 to 33.3 C during the nesting season. A characteristic daily range was from a low of 26.0 to a high of 30.5 C.

Although nest building was not observed for this species, the finished nest of C. brachyura is so similar to that of all other New World species in the genus that the building process must also be highly similar. The best studied species, C. pelagica, collects nesting material by grasping tree-top

twigs in its feet and breaking them off while in flight (Fischer, 1958). The nest is made entirely of such twigs glued together and affixed to a vertical surface by means of a secretion of the sublingual salivary glands. C. brachyura shows a pronounced enlargement of these glands during the breeding season, as has been reported for C. pelagica (Johnston, 1958) and several species of Collocalia (Medway, 1962c).

The nest of C. brachyura is a shallow half-saucer of twigs which are 20-75 mm long and usually only 1-2 mm in diameter (Fig. 3). It is slightly smaller than the nests described for other species of Chaetura (Table 1). The nests were glued to the walls of the manholes at varying heights, some being near the top where they were in deep shadow and others






15























































Fig. 3. Nests of Chaetura brachyura.







16





Table 1. Nest dimensions of swifts of the genus Chaetura.
(W) width of nest at greatest point along rim, (FB) greatest distance from back to front rim, (D) greatest depth from rim to bottom of nest. Measurements in centimeters.


Number
of
nests Average Range


C. brachyura
W 6.2 5.4 6.9 FB 8 5.3 4.0 6.5 D 2.5 1.8 3.3

C. pelagical
W -- 7.5 -11.3
FB -- 5.0 7.5 D -- 2.5 3.1

C. vauxi2
W 10.0 -FB 1 6.0 -D 4.0 -C. andrei3
W 8.5 7.5 9.5
FB 3 4.3 3.5 5.0 D 3.7 2.5 3.0

C. chapmani4
W 6.9 -FB 1 5.9 -D 2.4 -lFischer, 1958; Bendire, 1895 2Dickinson, 1951
3Sick, 1959
4Collins, unpub.






17


as much as 10 feet down where they often received direct sunlight for part of the day. Nests were occasionally re-used in successive years but in most cases they peeled off the wall soon after the nesting season. Before re-use additional twigs appeared to be added to the nest, as has been recorded for C. pelagica (Amadon, 1936; Fischer, 1958). In but a few cases did C. brachyura build up the semicircular arch of saliva on the wall above the nest so diagnostic of C. pelagica nests (Fischer, 1958; Fig. 8). The absence of this additional support may account for the more rapid destruction of C. brachyura nests. Egg laying starts about 10 days after the beginning of construction and before the nest is completely finished. The nests are unlined, but in two cases a feather was found glued in among the sticks, and a large white feather was once found in the bottom of a nest containing recently hatched young.

A variety of other organisms were also found in the manhole nest sites. Those holes that were partially filled with water usually contained the tree frog Hyla rubra. An unidentified snake and a lizard, Ameiva ameiva, were each seen on one occasion at the bottom of dry holes, presumably having gotten there through the connecting drainage pipe. Wet and dry holes alike often contained one or more nests of the "Jack Spaniard" or paper wasp (Polistes canadensis), under the overhanging edge of the top and the globular mud nest of the potter wasp (Eumenes canaliculatus), on the walls. Spiders of several types frequented the manholes, and on one occasion Snow (1962) observed a large spider (Mygale sp.) pounce on and kill a






18

nestling which fell out of the nest.


Cypseloides rutilus

The nests of four of the ten species presently included in the genus Cypseloides are still unknown. There is, however, a good deal of similarity in both site and nest material among those that have been described. Lack, in his review of the nesting habits of swifts (1956a), states that "all the species of Cypseloides for which the nest is reliably known agree in building on steep cliffs, usually in association with water, making a cone-shaped nest of mud and moss lined with ferntips or twigs." For Cypseloides niger (Gmelin), Knorr (1962) has delimited five "ecological requirements" for nest sites: "the presence of water, high relief . inaccessibility for terrestrial marauders, darkness, and lack of flyway obstructions in the vicinity of the nest." This type of nesting situation is so characteristic that numerous nests of C. niger have been successfully found by searching for these "ecological requirements" rather than birds showing indications of possible breeding (Michael, 1927; Knorr, 1961, 1962). The same procedure was used in this study to find additional C. rutilus nest sites in Trinidad and, I am sure, could be applied with equal success to locating the yet undescribed nests of C. biscutatus (Sclater), C. cherriei Ridgway, C. cryptus Zimmer, and C. lemosi Eisenmann and Lehmann. Only two nests attributed to Cypseloides are not in agreement with this general pattern or the descriptions of other nests of the same species. They represent one nest each of C. fumigatus (Streubel) (Holt, 1927-






19


1928) and C. zonaris (Shaw) (Todd and Carriker, 1922). In both cases the nests were described as being made of twigs glued together with saliva. The nest of the former also contained five young and was located inside a house gable, an improbable site and brood size for a species of Cypseloides. These nests are quite obviously more correctly referred to some species of Chaetura.

In the first description of the nest of C. rutilus, Orton (1871) states it to be "chiefly of moss, very compact, and shallow, and located in dark culverts about two feet above

the water." Belcher and Smooker (1936) characterize nests in Trinidad as "half cups stuck to a perpendicular wall of rock . over a swiftly running stream." Snow (1962) describes the nest as "a substantial bracket, semicircular in horizontal section with a wide depression for the eggs . [and]. . made of various plant fibers, usually including some moss."

My observations indicate some variation in the shape of C. rutilus nests. Some nests, built on smooth vertical surfaces, in fact resembled truncated cones similar to those of C. fumigatus and C. zonaris (Reboratti, 1918). Others, located on small rock ledges, were little more than pads of nesting material, somewhat thicker along the outer rim, with a wide but shallow cup for the eggs (Fig. 4). This type of nest closely resembles the "disk-shaped" ones reported for C. zonaris and C. niger when similarly located on damp rocky ledges (Rowley and Orr, 1965; Michael, 1927). The shape of







20





a.


























b.


























Fig. 4. Nests of Cypseloides rutilus; a) "Cone-shaped," b) "disk-shaped."






21


the nest, then, seems to be entirely dependent on whether it is affixed to a smooth rocky surface or perched on a narrow ledge. Larger species such as C. zonaris, require greater support for their nests and consequently would be expected to build on ledges when available. The smaller and lighter weight species such as C. rutilus and C. fumigatus, could also build cone-shaped nests fixed to vertical surfaces. Presumably owing to its extreme weight (170-180 g), the largest New World swift, Cypseloides semicollaris (Saussure), builds no nest at all and lays its eggs on sandy ledges in caves (Rowley and Orr, 1962).

Regardless of the shape, C. rutilus nests appeared to

be primarily of soft plant material with some mud intermixed. This mud presumably helped hold the nest material together and attach it to the rock as no salivary glue appeared to be used. The universal use of saliva in swift nest construction has already been questioned (Marshall and Folley, 1956; Johnston, 1961), and its use should not be assumed for C. rutilus until further information is available. The plant materials used in Trinidadian C. rutilus nests included a liverwort of the genus Plagiochilax, the lycopsids Selaginella cladorrhizans and S. cf. arthritica, and the filmy fern Trichomanes membranaceum. All of these plants grow in damp shady places, particularly on rocky outcrops along streams (Fig. 5) and thus in proximity to the nest sites of these swifts. There is no information available on the collection of the nest material or nest construction by any species of Cypseloides. Nests are used during several successive years, and a new lining of fresh green material is







22























































Fig. 5. Nesting material of Cypseloides rutilus growing on stream-side rock ledge.





23



added annually, with several distinct layers representing the annual additions. Sea cave nests of C. rutilus appeared to be constructed of slightly different materials and may well have contained seaweed as reported for a similarly located nest of C. niger (Legg, 1956).

C. rutilus nests have been found on rocky outcrops

overhanging pools in mountain streams (Fig. 6), on the rocky walls of a river gorge, in sea caves, and also in man-made culverts (Fig. 4a) and in one case on the underside of a bridge (Belcher and Smooker, 1936; Snow, 1962). In general the sites are similar to those for other species of Cypseloides in being in deep shadow, inaccessible to terrestrial animals, and closely associated with water. They do not strictly agree with the ecological "requirements" outlined for C. niger in that they are rarely associated with high relief. All nests of this species have been found in forested areas at localities of relatively low elevations from sea level to 1100 feet. Most nests were in deep shadow and none received direct sunlight. Streamside nests were only 2-4 feet above the water, but nests in a gorge were as much as 25 feet above the river, although still in a damp situation owing to seepage water on the walls.

The sea-cave nests were about 6-8 feet above either permanent water or tidal wash.

In contrast with the larger species C. zonaris and C. niger, which nest near, and sometimes behind, waterfalls, only one C. rutilus nest was near falling water. This nest was on a smooth wall about 8 feet above a pool of water, into which






24

















































Fig. 6. Stream nesting habitat of Cypseloides rutilus.






25


poured a small waterfall, and just outside the spray zone of the fall. Of the 15 nest sites observed during this study 2 were along mountain streams, 6 were in a river gorge, 4 in sea caves, and 3 were in man-made culverts under a road or under a bridge. Nine of these sites were found by Snow (1962).

The largest concentration of nests was in the rocky

walled "guacharo gorge" cut into limestone by the Arima River near the head of Arima Valley. This gorge is located on the Spring Hill Estate and has 'been a nesting place for these swifts for at least 40 years, a nest being reported from there in 1926 (Belcher and Smooker, 1936). Individual nests were situated along the gorge at varying intervals the least being about 35 feet. Elsewhere, the least distance I have recorded between two active C. rutilus nests was about 7 feet. In this case the two nests were on the walls of a cave-like rock archway

8 feet above a channel of water which cuts through Saut D'Eau Island, an offshore islet on the north coast of Trinidad. It is noteworthy that these swifts had to cross about a quarter mile of ocean to reach the nearest feeding area. The swifts inhabiting sea caves on Huevos Island probably also crossed stretches of water in getting to mainland feeding area.

The most prominent organisms sharing these nest sites were a variety of bats (mostly of the family Phyllostomidae) which used the shady areas as daytime roosts. Several species of small frogs and a cave cricket could be found in the vicinity of the nest sites. On one occasion a small snake, Leptodeira




d






26


annulata, was caught on a ledge only a few feet from an active swift nest. As its name implies, the "guacharo gorge" also contained a small colony of the guacharo or oilbird, Steatornis caripensis, as did two of the sea caves in which C. rutilus was thought to nest (Snow, 1962).

Environmental temperatures at typical C. rutilus nest sites ranged from 18.8-26.2 C, but had a characteristic daily range of 21.5-25.0 C. Sea cave nest sites tended to be a bit warmer, with maximum temperatures reaching 27.2 C. The range in temperature recorded over 13 months at one nest site in the river gorge was 18.8-23.8 C. Relative humidity at the nest sites was always in excess of 95 per cent.
















BREEDING SEASONS


Most land birds in Trinidad have a well defined breeding season. In contrast to the annual period of molt which shows little yearly variation, the breeding season varies considerably from species to species and from year to year (Snow and Snow, 1964). The breeding seasons for the two swifts C. brachyura and C. rutilus extend from April until late August or early September but vary within this period considerably from year to year. The season coincides with the height of the annual rainy period when insects are presumably most abundant, and it probably represents an adaptive synchronization that assures adequate food when young are to be fed. A similar adaptive relationship seems to exist in Trinidad with the swallows, which also depend upon flying insects for their food (Snow and Snow, 1964).

Although the ultimate factor regulating the breeding season seems to be an abundant food supply at the time of nestling growth, the proximate environmental factors are more obscure. The role of photoperiod as a proximate factor controlling breeding in tropical and equatorial birds is still subject to debate. Experimental work has shown that the gonads

of several low-latitude birds respond to increasing photoperiods, as has been amply shown for temperate latitude birds (Marshall 27






28


and Disney, 1956; Miller, 1959). However, the small annual change in photoperiod at the lower latitudes makes it reasonable

to assume that these swifts and possibly other tropical birds respond to a combination of photoperiod and some more variable environmental stimulus similar to the situation in the erratically breeding red crossbill, Loxia curivostra, of the temperate zone. This crossbill shows only a partial response to increasing or constant long photoperiods. The completion of gonadal development and the triggering of breeding is dependent upon some proximate environmental factor as an increased availability of suitable food (Tordoff and Dawson, 1965).

The most obvious environmental factor potentially

regulating the breeding of these Trinidadian swifts is the onset of the annual rainy season. Even so, the response of each of these two species is somewhat different. C. brachyura usually begins nesting before C. rutilus and very soon after the first heavy rains of the season. The first sign of breeding activity is the appearance of new nests or in some cases the addition of new material to old nests. These activities coincide with the start of the summer rainy season, and in those years when brief heavy rains precede the period of intense

summer rainfall, C. brachyura often begins nesting at an earlier date. For example, in 1959, there were heavy rains early in

April followed by a dry spell until the beginning of the true summer rains in the middle of May. This false start triggered breeding by C. brachyura in April followed by a lull during the

dry spell and renewal of nesting activity in late May (Snow,






29


1962). In 1964 when there was an extremely wet winter and spring, particularly in the more easterly parts of Trinidad,

the breeding activities of C. brachyura began very early, although the main rainy season did not appear to start until late May. A summary of the number of C. brachyura nests begun in the years 1957 to 1964 in half-month intervals is presented in Table 2. Several other Trinidadian birds appeared to be

directly influenced by the return of rainy weather. In several cases the first strong rains of the season triggered reproductive activity. Almost immediately nest building and the gathering of nest material was conspicuous and a peak in the number of eggs laid soon followed (Snow and Snow, 1964). Temporary dry spells also sharply reduced breeding in several

species.

C. rutilus started its breeding activities later than C. brachyura and in most years showed a greater population

synchrony (Table 3). The first sign of their renewed nesting was always the appearance of a fresh lining of greenery in the old nests in preparation for their re-use. Prior to the start

of the rains this material is in short supply since much of it dies away during the dry season and regains its previous lushness only when the rains return. It appears that C. rutilus depends upon the reappearance of suitable nest material to begin its breeding cycle. Such plant material is in turn dependent upon the return of the full summer rains and in some cases the rising of water levels in the streams.







30








Table 2. Distribution of Chaetura brachyura nests in halfmonth intervals.


All
Period 1957* 1958* 1959* 1960* 1961* 1962 1963 1964
Years

1 -15 April 1 1 2 16-30 April 1 1 3 2 7 1 -15 May 5 4 1 3 1 2 4 4 24 16-31 May 4 3 2 3 2 1 2 4 21 1 -15 June 1 4 3 4 2 14 16-30 June 1 1 5 1 2 4 1 15 1 -15 July 3 2 1 3 3 1 13 16-31 July 1 4 2 1 1 1 ** 1 11 1 -15 Aug. 3 1 2 3 1 ** 1 11 16-31 Aug. 3 1 ** 4 1 -15 Sept. 1 1 1 ** 3


Total 19 16 16 14 21 13 12 14 125


*Data from Snow (1962)
**No observations






31









Table 3. Distribution of Cypseloides rutilus nests in halfmonth intervals

All
Period 1957* 1958* 1958* 1960* 1961* 1962 1963 1964 Years


1 -15 April

16-30 April 1 1 1 -15 May 1 1 1 3 16-31 May 1 1 2 1 5 6 16 1 -15 June 1 1 2 3 5 1 13 16-30 June 1 2 1 2 6 1 -15 July 2 1 3 16-31 July 2 1 2 1 2 ** 8 1 -15 Aug. 1 1 1 2 1 1 ** 4 11 16-31 Aug. 1 3 2 ** 2 8


Total 2 9 7 8 9 11 10 13 69


*Data from Snow (1962)
**No observations






32


This sequence of events was particularly noticeable

in 1964. In that year the easterly parts of Trinidad experienced a very wet winter and spring. As mentioned (p 29), this unseasonable wet weather stimulated very early breeding by C. brachyura in that area. At the same time Arima Valley had a fairly normal dry season which did not end until 22-23 May.

These two days were marked by nearlydcontinuous heavy rains. Prior to this time there had been no indication of breeding that year at any known C. rutilus nest site in the valley.

The stream water levels were low and suitable nest material was unavailable. Several days after these first heavy rains the mossy stream-side plant life had recovered a great measure of its former lushness. On 29 May six C. rutilus nest sites were checked and all six nests were relined with fresh greenery. On 3 June three of these contained one or more eggs. By 6 June four of the six nests had full clutches while a fifth contained

a partial clutch. The remaining nest, although relined, was not used that year.















CLUTCH SIZE


Like other species of Chaetura, C. brachyura lays

large clutches. The 26 complete clutches observed from 1962 to 1964 ranged from 2-7 eggs, with a mean clutch size of 3.8

(Table 4). This is slightly less than for the other Chaetura species that have been studied (Table 5). In the earlier observations on this same population from 1957 to 1961, 41 clutches ranged in size from 1-6 and had a mean of 3.6 eggs per clutch (Snow, 1962; Table 2). Unusual clutches of 8 and

9 have been recorded for C. pelagica and C. brachyura, respectively, but in each case they appeared to result from two females laying in the same nest (Fischer, 1958; Snow, 1962). The 7-egg clutches recorded for C. vauxi (Baldwin and Zaczkowski, 1963) and C. brachyura (this study) both seemed to be the product of a single female. In both of these cases the eggs were laid or hatched within a short time of each other.

An additional example of two females laying in a single nest was noted for C. brachyura in 1963. In this case a clutch of 4 eggs was laid in a newly constructed nest between 7-13 May at the usual rate of 1 egg every other day. Incubation began on 14 or 15 May, and the clutch still consisted of only 4 eggs on 17 May. On 21 May, however, a fifth egg was noticed and when the nest was checked on 23 May a sixth had been added.

33






34









Table 4. Distribution of clutch sizes of Chaetura brachyura
by half-month intervals for years 1962 to 1964.


Clutch Size
Period 1 2 3 4 5 6 7 Totals


16-30 April 1 1 2 1 -15 May 1 2 2 5 16-31 May 1 1 3 1 6 1 -15 June 1 1 16-30 June 2 1 1 4 1 -15 July 2 1 1 4 16-31 July 1 1 2 1 -15 Aug. 1 1 16-31 Aug. 1 1


All months 0 3 8 8 5 1 1 26






35









Table 5. Clutch size of swift species in the genus Chaetura.


Number Average
of clutch
Species clutches Range size Reference


C. pelagica 25 2 5 4.2 Fischer, 1958

27 3 7 4.0 Dexter (in Fischer, 1958)

19 4 6 5.3 Sherman, 1952 C. brachyura 41 1 6 3.6 Snow, 1962

26 2 7 3.8 this study C. andrei 3 4 5 4.6 Sick, 1959 C. vauxi ? 3 7 ? Baldwin & Zaczkowski, 1963; Bent, 1940.






36


Four two-day-old young and two eggs were in the nest on 2 June, after an incubation period of approximately 17 days. The remaining two eggs hatched on 6 and 7 June and both of the newly hatched young birds were found later the same day dead or nearly dead on the floor of the nest cavity. Presumably they were inadvertently shoved out of the nest by the movements of the older and stronger nestlings. An evening check of this nest showed three adults roosting together near the nest; one of them was known to be a yearling bird raised in that nest cavity the

preceding year.

Two females trying to lay in the same nest may have caused disruption of egg laying and ejection of eggs in two other cases. Adult birds were frequently observed roosting in nest cavities with a nesting pair, although not in close approximation. At three additional nests extraparental cooperation was observed in the feeding of the young.

In C. pelagica extraparental cooperation occurs regularly and may involve birds of all ages and both sexes including young of the previous year. These helpers share in the incubation and brooding duties as well as the feeding of the young (Dexter, 1952). Further observations with individually marked birds might well show it to be of regular occurrence in C. brachyura. The cause of such extraparental cooperation in Chaetura is not yet clear. It may be due to a shortage of nest sites as suggested by Snow (1962), or to the inability of some birds to find mates as suggested by Dexter (1952). Skutch (1961) feels that such activities in passerine birds may






37


represent an adaptive curtailment of the reproductive rate favoring the greater survival of a lesser number of young.

Eggs were usually laid at the rate of one every other day. On a few occasions disturbances of the nest or inclement weather appeared to prolong the laying period. Five eggs in a single clutch weighed 1, 1, 1, 1-1/4 and 1-1/2 grams.

Clutch size in C. rutilus is very small, as is true of all species of Cypseloides. Of 25 clutches observed from 1962 to 1964, 23 were of 2 eggs and 2 of 1 egg. Of 32 clutches observed by Snow only one case of a clutch of a single egg was noticed and he attributed this to a bird breeding for the first time.

The interval between the laying of the two eggs was more irregular than for C. brachyura. The second egg of the clutch was usually laid two days after the first, but intervals of as long as five days occurred during which the first egg was left uncovered in the nest. The eggs from two clutches weighed 2-1/4, 2-3/4, 2-3/4 grams. Extraparental cooperation was not

observed in this species.
















INCUBATION


The incubation period was calculated from the laying of

the last egg to the hatching of the last young. For C. brachyura the 17-18 day period determined by Snow (1962) was confirmed, except in one case, when the period was only 16 days. A period of 48-72 hours usually elapsed between the hatching out of the first and last young.

The incubation period for all clutches of C. rutilus agreed with the 22-23 day period determined by Snow (1962). The siblings in the broods of two usually hatched within 24 hours of each other.

Although substantial losses often occurred during the incubation period, there was a high percentage of hatching among those eggs of both species which reached the expected date of hatching (Table 6). The figure recorded in this study for C. rutilus (84.3 per cent) is lower than that of Snow (93.1 per cent) because of the desertion of a clutch and it may have resulted from the greater frequency of disturbing visits. Thus the higher value may be more characteristic of undisturbed nests. The hatching rate, based on the total number of eggs, is quite low for both species as compared with similar values for other swifts (Table 6). Those species showing a high hatching success are also those with the more inaccessible 38






Table 6. Average hatching and fledging success of swift species.


Eggs hatched of Eggs hatched Young fledging Young fledging Species No. completely of No. laid of No. eggs of No. eggs incubated (9) (%) hatching (%) laid (%)


Apus apus
(England) -- 74.011 74.5 59.0 pus apus2
(Switzerland) -- 76.0 85.8 65.2 Apus melba3 94.4 86.0 80.9 76.0 Apus caffer4 98.9 88.6 86.0 76.2
(Kenyal
Apus caffer -- 81.0 70.3 57.0
(South Africa)
Cypsiurus parvus6 54.2 31.5 17.1 Chaetura pelagica7 -- 89.5 96.1 86.0 Chaetura brachyura8 95.0 51.7 53.5 26.7 Cypseloides rutilus9 93.1 -- -Cypseloides rutilus8 84.3 65.8 68.4 36.1 Collocalia maximalO -- 29.2 65.4 -Collocalia esculentalO -- 76.1 74.7 -Collocalia salanganalO -- 51.5 78.5 -ILack and Lack, 1951. 2Weitnauer 1947. 3Lack and Arn, 1947. 4Moreau, 1942a. 5Schmidt, 1965. 6Moreau, 1941. 7Fischer, 1958. 8This study. 9Snow, 1962. 10Medway, 1962a. 1178.0 per cent when eggs ejected prior to start of incubation are omitted.






40


nest sites. The higher hatching success of C. rutilus, compared to C. brachyura, is probably similarly based on the fact that C. rutilus nests overhang water on smooth surfaces or inaccessible ledges, and are less often disturbed by predators than the nests of C. brachyura in manholes or hollow trees. Several of the "inaccessible" sites recorded for other species were in man-made structures and may not, therefore, reflect mortality rates when

under natural conditions.















PARENTAL CARE


The period during which the young are under parental

care is divided into nestling and fledgling periods. The nestling period includes the time the young are in the nest. The fledgling period is when the young are out of the nest but incapable of flying and are still being fed by the adults. These periods are quite different in the two species of swifts in this

study. In C. brachyura there is a well defined nestling and fledgling period while in C. rutilus these two periods overlap..


Chaetura brachyura

Nestling period. The young of C, brachyura spend the

first three weeks of their lives in the nest. Some birds leave the nest as early as day 20 but most remain in it until 22-23 days after hatching. Those in larger broods tend to leave the nest sooner than those in smaller ones.

Fledgling period. C. brachyura has a fledgling period lasting about two weeks during which.the young are out of the nest clinging to the walls of the nest cavity. Most of the fledglings remain in the nest cavity until they are 30-36 days old, and occasional individuals stay until they are about 40 days old, even though they may be capable of leaving as early as 26 days after hatching. In one extreme case two young birds were still roosting in the nest cavity and being fed by the adults when 49 and 50 days old, respectively.
41






42


The ultimate factor governing departure of the fledglings is probably the cessation of feeding by the adults. Young birds quite capable of flying were observed to spend much or all of the day roosting in the nest cavity, so long as the adults continued to feed them. Several birds, which escaped while being handled, successfully flew away and yet were found again roosting on subsequent daytime visits. Snow (1962) also observed young birds to "return to their nest hole by day after their first flight." It is quite possible that young birds more than 30

days old, still found roosting by day, were making occasional short flights before entirely abandoning the nest cavity. Two

35-day-old swifts, caught boosting in their nest cavity, were fully capable of sustained flight at this age and successfully returned when released at a point nine miles away. The earlier observations by Snow (1962) indicated that "the young can fly if disturbed as early as 28 days after hatching;if undisturbed, they do not usually leave until they are 30-40 days old."


Cypseloides rutilus

In C. rutilus, as in all swifts except species of

Chaetura, there is no separation of the nestling and fledgling periods as the young remain in the nest until the time they can fly and feed themselves. This combined nestling-fledgling period in C. rutilus is somewhat longer than in C. brachyura, being closer to 40 days. All available figures exceed 35 days and most fall between 37-43 days, averaging 39-30 days. These figures are in agreement with those determined by Snow (1962). Young C.






43


rutilus have been seen on occasion to exercise their wings while "hanging to the outer rim of the nest" (Snow, 1962). Any attempts to clamber about on the rocky walls adjoining the nest would probably result in death, as these surfaces are usually smooth

and often wet and slippery.

The combined nestling-fledgling periods for most swifts are between 35-45 days, with larger species requiring slightly longer than smaller ones. Usually short periods of 29-32 days were noted for Cypsiurus parvus (Lichtenstein) and 30 days for Chaetura pelagica (Moreau, 1941; Fischer, 1958). Slight geographic variation in the nestling-fledgling period has been noted in Apus caffer (Lichtenstein), which averages 42 days in Kenya and 46 days in South Africa (Moreau, 1942a; Schmidt, 1965). Weather conditions can also affect the length of this period, bad weather extending it as much as two days (Lack, 1956b).














d















BROODING


Until they are about two weeks old, nestlings of both swift species are brooded at night by one or both parents. By this time the young are too large to be covered by the adults. During the first days of their life nestlings of C. brachyura are regularly brooded for long daytime periods, and for shorter periods, of 20 minutes duration or less, as late as 8 days after hatching. As early as the second day after hatching, however, both adults are sometimes absent, presumably foraging for the young. Nestlings of C. rutilus usually are continuously brooded during the daytime for the first 10-11 days, and occasionally as late as 13 days after hatching.

Most species of swifts brood during the daytime for

most of the first week of nestling life, although both adults may be absent for short periods, particularly around dusk. Thereafter, daytime brooding is sporadic and highly variable in duration. In England, daytime brooding was recorded in Apus apus for 98 per cent of the time during the first week of nestling life, up to 52 per cent during the second week, and 7 per cent or less thereafter.








44















FLEDGING SUCCESS


The mortality during the nestling and fledgling periods

for C. brachyura was approximately equal to that during incubation (Table 6). Only 53.5 per cent of the 58 hatchlings successfully fledged, and only 26.7 per cent of the 112 eggs laid resulted in fledged young. For C. rutilus the mortality rates of eggs and nestlings were also about equal, with 68.4 per cent of the 19 hatchlings successfully fledging, or only 36.1 per cent of the total of 36 eggs laid.

As indicated by Snow (1962), the figures for C. brachyura may not be typical of nests other than in man-made structures, and there may well have been some additional mortality resulting from the frequent visits and repeated handling which were part of this study. There is, however, no information available for

any species of Chaetura in a natural nest site. The only information on other Cypseloides swifts is for C. niger, which had a similarly high rate of nest failures, particularly in the nestling stage (Hunter and Baldwin, 1962).

The causes of egg and nestling losses are not clear.

At least one nestling of Cypseloides niger was seen to fall from the nest (Knorr, 1961:168), and it is possible that many of the losses of C. rutilus are similarly due to young birds accidentally falling out of the nest. This is less likely in C. brachyura in 45






46


light of the strength of their feet and their ability to hold tenaciously to the nest, even at very early ages.

No predation of eggs or nestlings has been observed for either species. Two nestlings of C. brachyura and one of C. rutilus were found that had been badly chewed by some animal. As these nests were inaccessible to terrestrial predators it is possible that this was the result of an attack by a bat of one of the several species which commonly roosted in close proximity to the swift nests. Other losses of both nestlings and eggs might also be attributed to bat predation. Skutch (1964) similarly suspected bats to be responsible for the disappearance of eggs and nestlings from the inaccessible nests and the wounding of a nestling of a hermit hummingbird. Some egg losses were also probably due to accidental ejection from the nest by the adults, as has been observed for other species (Lack and Lack, 1951; Moreau, 1942a).















GROWTH


Body weight

A total of 321 nestling weights was obtained in the

field, from a total of 57 chicks from 15 nests of C. brachyura (Fig. 7). From 1-15 weights were obtained from a single nestling. A total of 165 weights of C. rutilus nestlings was obtained from 25 individuals weighed between 1-16 times each (Fig. 8).

At hatching the average weight of C. brachyura nestlings was 1.6 grams and 18 days later it reached a maximum of 21.2 grams, a 13.3-fold increase. At fledging they had reached approximately 87 per cent of their adult weight.

The average weight of C. rutilus at hatching, was 2.1

grams, and it reached a maximum average weight of 26.2 grams on day 29, a 12.4-fold increase. At fledging C. rutilus weighed approximately 119 per cent of the adult weight.

The instantaneous percentage growth rate, calculated for each day (Brody, 1945: 508), tended to decrease in both species after an initial rise (Tables 7-8). C. brachyura had its peak growth rate on the fourth day after hatching: the similar peak for C. rutilus did not occur until the seventh day. The average weight gain per day and the average per cent growth rate per day were calculated for 7 five-day periods during the nestling life of these two species (Table 9). These

47










251

20 15


10 8
9:
<7 Z5

S4 CHAETURA BRACHYURA

3


2






0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 AGE IN DAYS Fig. 7. Growth curve of Chaetura brachyura. Semi-log plot, vertical lines
represent range of daily weights, curve connects daily means.














15


I0 9
U) 8
7 6 (.95

:4 GYPSELOIDES RUTILUS

3


2






0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 AGE IN DAYS

Fig. 8. Growth curve of Cypseloides rutilus. Semi-log plot, vertical lines
represent range of daily weights, curve connects daily means.






50


Table 7. Daily weight (grams) and relative growth rate (per cent) of Chaetura brachyura.


Mean Per cent relaDays from Mean weight tive growth hatching No. weight Range change per day


0 20 1.6 1 0 -2.1/2 -- -1 18 2.1 1 1/4-2.3/5 0.5 27.1 2 13 2.8 2 1/4-3 1/2 0.7 28.7 3 10 3.7 2 1/4-4 1/2 0.9 27.8 4 10 5.1 3 1/2-6 1/4 1.4 34.0 5 10 6.3 5 3/4-7 1/4 1.2 19.1 6 8 7.4 6 -9 1.1 16.0 7 9 8.7 4 -11 1.3 16.1 8 16 11.1 8 1/4-15 2.4 24.3 9 9 11.2 5 1/2-15 0.1 0.8 10 15 13.5 11 1/2-16 3/4 2.3 18.6 11 14 16.1 13 -19 1/2 2.6 17.6 12 14 16.2 13 1/2-19. 0.1 0.6 13 7 18.3 15 3/4-20 2.1 12.1 14 9 19.0 17 1/2-21 3/4 0.7 3.7 15 11 18.1 13 -22 1/4 -0.9 8.6 16 8 19.1 17 1/2-21 1/2 1.0 13.9 17 7 19.6 18 -22 0.5 2.5 18 6 22.2 17 3/4-22 1/2 2.6 12.4 19 7 20.2 17 1/2-23 3/4 -2.0 9.4 20 5 20.9 19 1/2-23 0.7 3.4 21 7 20.2 17 3/4-22 1/2 -0.7 3.4 22 6 19.0 17 1/4-22 1/2 -1.2 9.5 23 5 18.9 16 -21 -0.1 0.5 24 8 18.8 13 3/4-21 1/4 -0.1 0.5 25 11 19.7 16 -21 0.9 4.6 26 7 19.0 15 1/2-21 1/4 -0.7 3.6 27 7 19.4 17 1/2-23 0.4 2.0 28 6 18.0 17 -20 -1.4 7.4 29 6 18.7 17 1/4-21 3/4 0.7 3.9 30 6 18.4 16 1/4-20 1/4 -0.3 1.6 31 7 16.5 14 1/4-18 1/2 -1.9 -10.8 32 3 17.0 16 -18 1/2 0.5 2.9 33 5 16.6 15 -17 3/4 -0.4 2.3 34 4 15.7 14 1/4-17 -0.9 5.5 35 4 15.4 13 -17 -0.3 1.9 36 1 16.0 -- 0.6 3.8 37 2 14.3 13 1/2-15 -1.7 -11.2


d







51


Table 8. Daily weight (grams) and relative growth rate (per
cent) of Cypseloides rutilus.


Mean Per cent relaDays from Mean, weight tive growth hatching No. weight Range change. per day


0 7 2.1 2 -2 1/2 -- -1 10 2.5 2 -3 0.4 17.4 2 7 3.5 2 3/4-4 1/2 1.0 33.6 3 10 3.9 3 1/4 -5 0.4 10.8 4 8 5.0 4 1/4 -6 1/4 1.1 24.8 5 13 6.3 5 1/2 -7 3/4 1.3 23.1 6 7 7.3 6 1/2 -8 3/4 1.0 14.7 7 7 10.6 8 -14 1/2 3.3 38.2 8 4 9.8 8 1/2 -12 1/4 -0.8 8.7 9 10 11.6 8 -13 1.8 16.8
10 3 12.8 9 3/4 -14 1/4 1.2 9.8 11 7 14.1 11 1/2-16 1.3 9.6 12 6 15.8 14 -18 1/2 1.7 11.3 13 6 16.6 14 1/2-17 3/4 0.8 4.9 14 4 18.2 17 -19 3/4 1.6 9.2 15 1 20.5 -- 2.3 11.9 16 6 20.7 18 1/2-21 1/2 0.2 0.9 17 1 19.3 -- -1.4 7.0 18 6 21.0 20 -22 1.7 8.4 19 4 21.2 18 -26 3/4 0.2 9.3 20 4 23.9 21 1/2-24 3/4 2.7 11.9 21 6 22.5 18 1/2-26 -1.4 6.0 22 2 20.8 20 1/4-21 1/4 -1.7 7.8 23 3 25.5 25 -27 1/2 4.7 20.3 24 1 23.0 -- -2.5 -10.3 25 3 25.2 24 3/4-25 3/4 2.2 9.1
26 -- -- -- -- -27 3 24.2 24 -25 -1.0 4.0 28 1 24.0 -- -0.2 0.8 29 3 26.2 23 1/4-28 3/4 2.2 8.7 30 4 23.6 22 1/2-26 1/4 -2.6 -10.4
31 -- -- - ..
32 1 20.3 -- -3.3 -15.0
33 -- -- -34 3 24.4 23 -26 1/2 4.1 18.3 35 1 24.0 -- -0.4 1.6 36 2 23.9 22 1/2-25 1/4 -0.1 0.4 37 1 24.3 -- 0.4 1.6






52








Table 9. Average daily growth rate (grams) and relative growth rate (per cent) for five-day intervals for Cypseloides rutilus
and Chaetura brachyura.

C. brachyura C. rutilus
Mean daily Mean daily Mean daily Mean daily
weight relative weight relative
Age change growth rate change growth rate 0-4 0.9 29.4 0.7 21.7 5-9 1.2 15.3 1.3 16.8 10-14 1.6 10.5 1.3 9.0 15-19 0.2 2.5 0.6 4.7 20-24 -0.3 -2.1 0.4 1.6 25-29 -0.02 -0.1 0.8 3.3 30-34 -0.6 -3.5 -0.4 -2.3






53


figures show that C. brachyura has an initially higher average daily weight gain and average per cent growth rate that subsequently decline rapidly. After approximately three weeks of nestling life the young begin to los6 weight, particularly when they first leave the nest and again later when they begin to fly. C. rutilus, on the other hand, has an initially lower average daily weight gain and average percent growth rate which also declines although at a slower rate so that the nestlings do not begin to lose weight until late in the nestling period approximately 4 1/2 weeks after hatching.

The general pattern of growth shown by these two swifts is similar to those reported for most altricial birds, particularly those with longer periods of development (Dawson and Evans, 1957, 1960; Maher, 1964; Kahl, 1958). C. brachyura is nearly identical in growth pattern to C. pelagica and C. vauxi, the only previously studied species of Chaetura (Fischer, 1958; Baldwin and Zaczkowski, 1963). C. rutilus is most similar in growth pattern to European species in the genus Apus with similarly long fledging periods (Lack and Lack, 1951; Weitnauer, 1947). No information is available for any other Cypseloides species.


General development

Feathers. Like other species of swifts, C. brachyura and C. rutilus are hatched naked. Approximately 4 days after hatching the developing contour feathers appear under the skin as dark dots along the feather tracts. The remiges are first






54


to break through the skin, usually doing so around day 4-5. The rectrices are somewhat slower, emerging on about day 6-7, followed by the contour plumage when the birds are about 8 days

old. The feathers of the dorsal tract grow somewhat faster than those of the cervical, capital, and ventral tracts and begin to emerge from their sheaths about 15-16 days after the young hatch. Emergence in the remaining tracts is somewhat later. The flight feathers begin to break out of their sheaths 12-13 days after hatching. The growth of the wing is shown in Fig. 9 and the tail in Fig. 10. The tail completes its growth about 26-27 days after hatching, but the wing does not reach full length until shortly after fledging.

C. rutilus acquires its feather covering in a sequence generally similar to that of C. brachyura but it differs slightly in timing. The remiges first break through the skin on about day 5, and the rectrices about 9 days after hatching. The contour plumage first appears as dark subcutaneous streaks and emerges through the skin about 10-11 days after hatching. The flight feathers begin to emerge from their sheaths about 13-14 days after hatching, about one day later than noted for C. brachyura. The contour feathers, however, begin to break through their sheaths much earlier in C. rutilus despite their having emerged through the skin somewhat later than in C. brachyura. These feathers begin to erupt 13 days after hatching as opposed

to day 15-16 for C. brachyura. The contour feathers of C. rutilus on the cervical, capital, and ventral tracts are somewhat slower in their development than those of the dorsal tract,












120


g -,,

4----*^
2 90 '/ C. BRACHYURA .-'



Z 60 I
-J

z ---- C. RUTILUS



1*" I
30


15


0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I i i
0 5 10 15 2 0 25 30 35 AGE IN DAYS

Fig. 9. Growth of the wing of Chaetura brachyura and Cypseloides rutilus.
Vertical lines represent ranges, curves connect daily means. Wing length
measured along chord from carpal joint to tip of longest primary.









45- 7


40


35- F ,"
3 , 230
z C. BRACHYURA -T 25
(.9 WIJ 20"
-JI I

-5 ,'. *--* C. RUTILUS I I,




5
0-4


0 2 4 6 8 10 15 20 25 30 35 AGE IN DAYS

Fig. 10. Growth of the tail of Chaetura brachyura and Cypseloides rutilus. O
Vertical lines represent ranges, curves connect daily means.





57


as also noted for C. brachyura. The tail reaches its full length about the time the young fledges (Fig. 9), but the wing does not complete its growth until early in the post-fledging period (Fig. 10).

The major difference in the plumage development of

Chaetura and Cypseloides species is the appearance in the latter group of a dark gray, down-like covering early in nestling life,

prior to the appearance of the regular contour feathers. Although referred to as natal down by earlier observers it has been shown to consist of a loose-webbed semiplume type of feather and forms part of the first teleoptile plumage (Collins, 1963). These feathers appear as subcutaneous dots as early as

the first day of nestling life. They may break through the skin as early as 5-6 days after hatching although usually somewhat later. They routinely emerge earlier than the previous estimate of 8-9 days after hatching (Collins, 1963). These semiplumes are freed of their sheaths for more than half of their length shortly after they erupt from the skin, and thus the nestling soon takes on a downy appearance (Collins, 1963; Fig. 3). The semiplumes seem to reach their full length of about 13-14 mm by day 19 and are entirely freed of their sheaths by day 26.

They are covered by the emerging contour plumage at about 28 days after hatching. Semiplumes are longest on the back and rump and shorter on the head and underparts. They are found on the margins of the pterylae, particularly on the dorsal aspect of the body. Although semiplumes are generally absent from

the wings, there are occasionally a few along the lateral,






58


margin of the humeral tract and a short row of them in the apterium between the lesser secondary coverts and the marginal coverts (Collins, 1965). A similar down-like plumage has been recorded for other Cypseloides species (Hunter and Baldwin, 1962; Orr, in litt.) and probably occurs in all members of the

genus. The semiplume covering and the early emergence of the contour feathers from their sheaths are aids to thermoregulation in nestlings living in a cooler microclimate.

Eyes. The two species have a noticeable difference in the opening of the eyes. Those of C. brachyura are partially open on day 16 and completely open on day 18. This is slightly later than has been observed for other species of Chaetura (Fischer, 1958; Baldwin and Zaczkowski, 1963). In C. rutilus they open gradually with an interval of more than a week between the first partial opening and complete opening of the eyes. In this species the young may have partially opened eyes as early as day 7, but usually this first occurs on day 8-9. Their eyes are not fully open until about 16-17 days after hatching.

Bill and feet. The newly hatched swifts of both species are pale flesh pink except for the bill and claws which have a slight gray pigmentation at the tip, especially apparent in C. brachyura. The lining of the mouth is also a flesh pink. In

both species a prominent egg tooth is present on the upper mandible (similar structures were reported in other genera by Parkes and Clark, 1964), and a hardened whitish cap occurs on

the lower mandible. The egg teeth gradually disappear during






59


the first weeks of nestling life. Both egg teeth are generally unobservable by day 14, although a -slight roughness on the culmen sometimes can be detected on slightly older birds.

Grasping with the feet was noticed on the first day after

hatching in both species. The legs of C. brachyura seem to be particularly well developed even very early in life and are capable of supporting the nestling on a vertical surface within 48 hours after hatching. The feet of C. rutilus cannot support a nestling in a similar fashion until about day 14. Michael (1933) similarly noticed that Cypseloides niger had "the dainty feet and slender legs of a songbird" and not the stronger limbs characteristic of the white-throated swift, Aeronautes saxatilis (Woodhouse). In their study of Chaetura vauxi, Baldwin and Hunter (1963) also comment upon the particularly sharp claws and strong toes as compared to Cypseloides niger. As was also found in this study, Baldwin and Hunter (1963) note that the young of Chaetura held on to the twigs of the nest so tenaciously that a loss of claws was likely to result if care were not taken in removing them from the nest. The strong feet of Chaetura are an obvious adaptation enabling them to raise a larger brood in their small nests. The ability to hold tightly to the nest reduces the chances of one of a large brood being accidentally jostled out of the nest, particularly during defecation. When the nestlings are older and the nest becomes overcrowded (Fig. lla) their strong feet enable them to climb out and support themselves on the wall nearby until actual fledging (Fig. llb).






60







a.


p




















b























Fig. 11. Chaetura brachyura nestlings and fledglings. a) in the nest shortly before leaving, b) on wall near nest.






61


Behavior. The vocalizations of these nestling swifts are quite limited. C. rutilus nestlings only make a very soft twittering when disturbed and give no calls during feeding. By comparison C. brachyura nestlings utter a prolonged loud rasping rattle when disturbed and particularly during feeding. This call starts and stops abruptly, and if one bird starts, its nest-mates are quick to join in. This "disturbance" call (Fischer, 1958) is restricted to the time of feeding and its associated activity and excitement once the eyes are open. Prior to this the slightest disturbance, whether an external influence or merely the sudden activity of one member of the brood, may trigger this call, which can be heard at some distance.

Neither of these swifts foul the nest during the nestling period. Fecal wastes are carefully voided over the rim of the nest by the young swifts. As noted by others this often results in large accumulations of trash under the nests. Much of the material found below swift nests, however, consists of the chitinous remains of their insect food and does not appear to have passed through the digestive tract. Legg (1956) found insect remains around a nest of Cypseloides niger, part of which appeared to be in the form of a pellet. Thus it seems probable that swifts, like many other insectivorous birds, regurgitate pellets made up of the indigestible chitinous portions of their insect prey and that much of the material accumulated under their nests, or in some cases in the nest (Rowley and Orr, 1965), comes from these pellets.






62


Development of Homeothermy


Young swifts of both species essentially lack any

thermoregulatory capacity at hatching. When they are not brooded their body temperature quickly drops to near ambient temperature (Figs. 12-13). Body temperatures as low as 2527 C were recorded for C. rutilus; the lowest body temperature recorded for C. brachyura nestlings was 31.9 C. The thermoregulatory capacity of both species improves as they grow older, and at the end of the third week of nestling life there is little

decline in body temperature even during extended periods without brooding.

Nestlings tested in a cold chamber (Fig. 1) at approximately 5 C showed rapid decreases in body temperature, as much as 9.8 degrees within 5 minutes. A total of 101 tests were made on 31 nestlings of C. brachyura and 72 tests on 12 C. rutilus. The rate at which body temperature dropped lessened sharply with increasing age (Fig..14). This lessening in temperature decline

represented an increase in the thermoregulatory capacity of the nestlings through both an increased capacity for thermogenesis and decreased heat loss. The decrease in body heat loss could be due to the appearance of an insulating feather coat or a decrease in the surface to volume ratio of the nestling. C. rutilus seems to have an efficient coat of insulation early in nestling life in the form of a down-like semiplume covering. In addition, its contour plumage grows in very rapidly. C. rutilus and C. brachyura, however, perfect their thermoregulatory














40


o 38




cr
W 36
0. CHAETURA BRACHYURA

I- 32

O
O 30



0 2 4 6 8 10 12 14 16 18 20 22 AGE IN DAYS

Fig. 12. Body temperatures of nestlings of Chaetura brachyura when
unbrooded.. Vertical lines represent daily range in body temperatures,
curve connects daily means. Typical daily range in ambient temperature
26.0-30.5 C.







40




36


w 34




S30


28- CYPSELOIDES RUTILUS
o
26 24


0 .2 4 6 8 10 12 14 16 18 20 22 AGE IN DAYS Fig. 13. Body temperatures of nestlings of Cypseloides rutilus
when unbrooded. Vertical lines represent daily range in body temperatures, curve connects daily means. Typical daily range
in ambient temperature 21.0-25.0 C.








10 32 33


SiC. BRACHYURA
8

35 C. RUTILUS




H21






o2 7




0





0-5 6-II 12-17 18-23 AGE IN DAYS

Fig. 14. Decrease in body temperature of nestling swifts under cold stress.
Vertical line represents the range, and rectangles two standard errors on
either side of the mean.
either side of the mean,






66


capacities at about the same rate and there is little difference in their body weight, and hence surface to volume ratio, during their first two weeks of life. Thus it would seem that C. brachyura must depend upon increased heat production to counteract the effects of cold environmental temperatures. As the environmental temperatures of their nest sites are usually quite

warm, they are only rarely exposed to such cold conditions and the need for increased thermogenesis.


Torpor

The insect food of swifts may be markedly affected by varying weather conditions. In the temperate regions, where acute food shortages lasting several days are of common occurrence, both adult and nestling swifts routinely drop their body temperatures at night and enter a state of torpor (Koskimies, 1950; Bartholomew, Howell, and Cade, 1957). The young of Apus apus can fast as long as 9 days by utilizing their stored fat deposits and decreasing their body temperature and metabolism at night (Koskimies, 1950). Similar reactions have been observed for several species of tropical swifts when deprived of food for several days in captivity (Howell, 1961; pers. obser.). Under natural conditions no healthy adult or nestling of either C. brachyura or C. rutilus exhibited a body temperature below the maximum that it was capable of maintaining, and none appeared to be in less than a fully active, awake condition. On several occasions nestlings which appeared to be injured or in an extremely weakened condition had abnormally low body temperatures.






67


In most cases these young were dead or missing from the nest at the next visit. The capacity for dropping into torpor may exist in all swifts, but it does not appear to be utilized in the normal course of events by either C. brachyura or C. rutilus.















ADULT WEIGHT


The average adult weight of C. brachyura, based on a sample of 240 individual weights, was 18.3 g with a range of 15 1/2-22 g. Snow (1962) reported an average weight of 19.8 g, but this value was influenced by the inclusion of a very fat, non-breeding female weighing 30 grams, a weight 8 g heavier than any other recorded for C. brachyura. This value is however, within the expected weight range of the extremely similar species Chaetura chapmani, to which perhaps it should be attributed. The average weight of 24 juveniles of C. brachyura, captured in roosting flocks of adults during September and October 1964, was not appreciably different from that of the adults although a few juvenile individuals ranged as low as 14-15 grams, which is below the minimal weight recorded for any adult.

The average adult weight of C. rutilus was 20.2 g and

ranged from 17 3/4-24 1/4 g in a sample of 45 individual weights. There was a slight sexual dimorphism, males being heavier than females. The weights of 24 males averaged 20.6 g and ranged from 19 1/4-22 1/4 g while 19 females averaged 19.6 g with a range of 17 3/4-24 1/4 grams. This difference is significant (P (.02).

Monthly mean weights for both sexes of C. brachyura



68






69


varied between a low of 17.1 g (Oct. 1964) and a high of 18.7 g (Aug. 1964). Daily means somewhat higher (18.9, 19.0 g) were also recorded during August 1964. Eighteen individuals weighed on two or three separate occasions, varied from as little as 1/4 g to as much as 2 1/2 g between successive weighings. Monthly mean weights of C. rutilus varied from a low of 19.6 g to a high of 20.7 g, while daily sample averages varied from 19.0 to 21.1 g, both in October 1964. Eight individuals weighed on two to four separate occasions varied as little as 1/4 g and as much as 2 1/2 g between weighings.

Weight variations of these magnitudes are explainable in terms of temporal variations in food availability. Similar weight changes were recorded for Apus apus in England (Gladwin and Nau, 1964) with sharp decreases in body weight being correlated with prolonged cold or rainy weather. Such weather greatly decreases the aerial food supply of these swifts (Lack and Owen, 1955). There was no marked seasonal change in weight between April and November in either C. brachyura or C. rutilus as is typical of migrant swifts, particularly C. pelagica in temperate North America (Coffey, 1958).
















FOOD AND FEEDING HABITS


A poorly known aspect of swift biology is their feeding habits. Although some information exists on the types of food collected and the rate at which it is brought to the young, there is only fragmentary information on where and at what rate it is collected.

In Trinidad, particularly during clear, sunny weather, mixed flocks of swifts are commonly seen moving up and down the valleys of the northern range, overhead at one instant, several miles away in a matter of minutes and back overhead shortly thereafter. During the summer rainy season these birds are often observed on the advancing edge of one of the intermittent showers so abundant at that time of the year. The flocks may. contain up to seven of the nine species of swifts recorded in Trinidad. These are only temporary associations, and if the birds are observed over longer periods certain specific feeding patterns can be seen.

Chaetura brachyura is by far the most widely distributed species in Trinidad and is observable at almost all elevations. It is the only Chaetura that regularly forages over the savanna areas and is decidedly more abundant there and over the lower parts of the northern range than over areas above 1200 feet elevation. One pair feeding young in a nest at an elevation of 500 feet in Arima Valley "used to fly off down the valley in the 70






71


direction of the savanna three miles away. They would return from the same direction" (Snow, 1962).

Cypseloides rutilus was less often observed in flight and then only in the upper part of Arima Valley or over the higher parts of the northern range. Even though it nests in caves at sea level on the north coast and at elevations of 500-1100 feet in Arima Valley, it seems to forage exclusively over the forest at higher elevations. Although the feeding ranges of the two species overlap at the lower elevations around 500 feet, C. rutilus is also comilonly observed at higher elevations including the summit of El Tuchuche (3,068 feet), whereas C. brachyura is uncommon above 1200 feet. Conversely, I have never observed C. rutilus over the savanna areas where C. brachyura is abundant. In addition to feeding at higher elevations, C. rutilus and another swift, Panyptila cayennensis (Gmelin), appear at all elevations to feed at greater distances above the ground than most species of Chaetura. This habit was also observed for C. rutilus in Trinidad (Snow, 1962) and for C. niger in Washington (Rathbun, 1925). As this characteristic of feeding at higher altitudes was most commonly noted during fine weather and particularly when both C. rutilus and P. cayennensis were part of mixed flocks containing one or more species of Chaetura, it may be less characteristic of their day to day feeding activities when not in association with other species.

In England, Apus apus generally feeds in the immediate vicinity of the nests (Lack and Owen, 1955), whereas Cypseloides niger makes daily trips of several miles from mountain nesting






72


areas to lowland feeding areas in Washington (Rathburn, 1925). During the breeding season both species also make long-range movements of several hundred miles to avoid prolonged adverse weather conditions (Lack, 1955; Udvardy, 1954). Chaetura pelagica in New York was seen foraging over a field about 1/4 mile from the nest and regularly brought in Ephemeroptera, presumably collected over a stream 1/8 mile away. Two color-marked birds were also seen foraging 2 3/4 and 4 miles, respectively, from their nests (Fischer, 1958).

Weather-influenced differences in the height of feeding have been noticed for Apus apus and C. niger, which feed higher in the air on sunny days and low over the ground or water during rainy or cloudy weather (Lack and Owen, 1955; Rathbun, 1925).

Day to day variations in feeding habits have been noticed for many species of swifts as they exploit temporary abundances in their air-born insect prey. They do not merely fly through the air, mouths open, catching only whatever happens to get scooped up. If closely observed, swifts can be seen to change their flight direction to snap up an attractive prey item. Confirmation of this is provided by the comparison of food

samples with random samples of aero-plankton. The swiftgathered samples are clearly richer in the larger species which are less characteristic of true aero-plankton (Lack, and Owen, 1955).

The foraging habits of C. brachyura and C. rutilus did not change noticeably from day to day although the swifts often descended to nearly ground level during wet weather to feed on






73


the large flights of winged reproductive termites. Feeding on this temporary plethora of food was not confined to the swifts. Numerous species, ranging in size from house wrens (Troglodytes aedon) to caciques (Psarocolius decumanus), also preyed on them. A similar array of birds was noted feeding on termite swarms in Panama (Eisenmann, 1961). On several occasions I observed

Chaetura brachyura to bank sharply up and flutter briefly near the outermost branches of trees extending above the forest canopy. It appeared that the birds were picking insects or spiders off the leaves. Similar foraging behavior was noticed for C. pelagica (Fischer, 1958) and may be widespread among

swifts.

Other swifts have been observed feeding in several less

typical ways. Apus apus has been noticed landing on the wall of a house and gathering spiders under the eaves (Meikeljohn, 1928), and foraging for insects and perhaps nest parasites in old swallow nests (Gilbert, 1944).

The stomach contents of the swifts collected during this

study were mostly masses of partially digested, poorly identifiable insect remains. On the other hand, the food brought to the nestlings was easily identified and probably consisted of the same

food consumed by the adults. The adults brought the food for the young swifts to the nest in their throat as a compact mass of undigested insects partially glued together by saliva. A total of 21 samples of the food brought to nestlings was collected, 17 from C. brachyura and 4 from C. rutilus. These samples were manipulated from the throat of recently fed nestlings. This






74


method, used earlier by Lack and Owen (1955), did not injure the the birds if done carefully and was not repeated frequently enough to disrupt the pattern of normal growth.

The contents of these samples were extremely varied (Table 10). Eight were homogeneous masses of either winged ants or winged termites. Heterogeneous samples varied from one or two types of insects to a mixture of some forty species representing six orders of insects and nine families of spiders. The samples varied in size from a nearly complete food ball of 326 insects to only a few remnants of a meal. Since it was not always possible to get complete food balls from the young birds, no comparison was made between the number or weight of food items brought in different trips. In four cases it was possible to get food samples from two C. brachyura nestlings of a single brood on a single visit to the nest. In each case both nestlings had received similar food. In the one case where samples were obtained on the same day from C. brachyura nestlings of different broods in nest sites about a mile apart, one nestling had received a homogeneous sample of winged ants while two nestlings

at the other site had both received mixed samples of Diptera, Coleoptera, and Hymenoptera. Day to day variation in the food brought in by a single pair of adults was extensive and usually

included both homogeneous and heterogeneous samples. No analysis of seasonal differences in food items was possible since these samples could only be collected while there were young birds in the nest.

Interspecific differences in the type of food collected






75

Table 10. Contents of food balls collected from nestlings of Chaetura brachyura and Cypseloides rutilus.


Number of
samples in which Number of Food item it occurred individuals


A. Chaetura brachyura

Araneae 2 94
Lycosidae 1 1 Tetragnathidae 1 1 Linyphiidae 1 1 Clubionidae 1 12 Micryphantidae 1' 2 Oxyopidae 1 2 Thomisidae 1 16 Salticidae 1 34 Theridiidae 1 1 Araneidae 1 3 unidentified 1 21

Coleoptera 6 73
Curculionidae 3 14
Apion sp. 1 1
Ceutorhynchus sp. 1 12
unidentified 1 1
Scolytidae 3 9
Cocotrypes sp. 2 7 unidentified 2 2
Cryptophagidae 1 2 Chrysomelidae 3 13
Lema sp. 1 3 Chaetocnema sp. 1 2 Systena sp. 2 2 Altica sp. 1 2 unidentified 1 4
Platypodidae 3 28
Platypus sp. 3 28
Staphylinidae 2 3 Coccinellidae 1 1 Nitidulidae 3 3
Stelidota sp. 1 1 Carpophilus sp. 2 2

Orthoptera 1 1

Hemiptera 2 10
Saldidae 1 1 Tingidae 1 9






76


-Table 10 (Continued)
,- ,

Number of
samples in which Number of Food item it occurred individuals


Homoptera 2 16
Membracidae 1 2 Aphidae 1 1 Cicadellidae 1 5
Deltocephalus flavicosta 1 1 unidentified 1 4
Delphacidae 2 8
Peregrinus maidus 1 1 Sogata sp. 1 1 unidentified 1 6

Diptera 12 402

Hymenoptera 16 203
Formicidae 12 128
Camponotus sp. 6 41 Trachymyrmex sp. 2 6 Leptalae elongata 2 15
unidentified 4 75

Isoptera 4 49
Kalotermitidae 1 1
Calcaritermes nigriceps 1 1
Rhinotermitidae 2 32
Coptotermes testareus 2 2 32
Termitidae 1 16
Nasutitermes costalis 1 16


B. Cypseloides rutilus

Hymenoptera 2 19
Formicidae 2 19
Dorymyrmex sp. 2 19

Isoptera 2 25
Rhinotermitidae 1 20
Dolichorhinotermes longilabius 1 20
Termitidae 1 5
Anoplotermes meridianus 1 2 Anoplotermes sp. 1 3






77


by these swifts is hard to assess accurately because of the difficulties encountered in collecting sufficient food samples from C. rutilus. A great variety of food items was utilized by C. brachyura in apparent contrast to C. rutilus. This difference is probably due to the accidental collection of nearly homogeneous samples of winged ants and termites from C. rutilus, and it is possible that additional samples would have shown a diversity of prey items equal to that of C. brachyura. Homogeneous food samples have been reported for several other species of swifts, and in no case were they typical of the normal day today diet. Thus they are only further indications of what has already been observed from the foraging behavior swifts are quick to feed on any temporarily abundant prey items, like mayflies (Ephemeroptera) or aphids (Homoptera: Aphidae) in temperate areas or winged ants (Hymenopterat Formicidae) and termites (Isoptera) in the tropical areas.

Not only do swifts feed on many different kinds of insects but also on a variety of sizes. Even so there seem to be certain limits to the sizes of prey items taken by any species of swift. The upper limit probably depends upon the size of the bird and what it could comfortably swallow.

All food items of C. brachyura and C. rutilus were

measured to check for possible size differences in their prey. The total length from the head to the tip of the abdomen, exclusive of antennae and legs, was taken as the best available indication of total size. All fractional measurements were read to the next whole millimeter. The range of sizes and abundance






78


of each size food item is shown in Fig. 13. As was true for the prey species diversity, C. brachyura appears to feed on a wider range of prey items than C. rutilus. Again it seems likely that this seeming difference is an artifact of the sampling. If only the similar food items (winged ants and termites) of the two swift species are compared (Fig. 15), the interspecific differences in the size of prey selected are not significant. Winged ants and termites appear in the food samples throughout the breeding season, and the absence of any difference in size of these food items selected by the swifts may indicate a similar absence of difference in size of other food items selected. If so, C. rutilus and C. brachyura would appear to select similar kinds and sizes of food items, although their foraging ranges

only partially overlap.

In England, Apus apus usually takes food items ranging in size from 2-10 mm, rarely larger or smaller. Within this

range it tends to take larger items from 5-8 mm long during fine weather when insects are abundant. During rainy or cold weather there are fewer insects available of all sizes, and the swift includes more of the smaller prey items from 2-5 mm in its diet (Lack and Owen, 1955).

From this it seems that larger species, such as Apus

apus, may occasionally select food items larger than any taken by either C. brachyura or C. rutilus and rarely take prey as small as some regularly taken by these smaller swifts. Similarly, 276 food items collected by another large swift, Cypseloides niger, in Veracruz, Mexico, ranged from 2-12 mm in length, with






79











.0

X *


TI-





>- .
<0 0 cr ::, .










Do



















0
N > *

40
















S.............
.... ...,.

























S1- -, 0 SVJ3.1 A3Wd ...40 UJ81JdN
tO0








*H) 4 H g
0c 4o

6 s0O 0
02D5

S64311 A3
N1






80


the most frequent sizes being 9 and 10 mm, or about the maximum size recorded for either C. brachyura or C. rutilus (Collins, unpubl.). If extended to other situations, two species of similar size would expectedly feed on insects within similar

size ranges. The food habits of Apus apus and A. pallidus (Shelley) support this idea. These 'two swifts are nearly equal in size and select similar sized prey items (G. B. Watson, pers. comm. ).















FEEDING OF YOUNG


The feeding of the nestlings was seen on several occasions but never close enough to be sure of details. Presumably it is similar to that reported for other swifts in that the adult carries the food to the nest in the mouth or throat. The adult inserts its bill into the mouth of the nestling and passes the food to it. As brought to the nest, the food items are often

glued together with saliva forming a compact wad or "food ball." Very young birds generally receive only part of a ball of food,

the rest being shared with other nestlings or retained by the adult. When older, a single nestling usually receives the entire

food ball.

The rate of feeding of C. brachyura is similar to that of

other species of Chaetura for which there is information. The intervals between visits of adults to the nest range from 2.545 minutes and average 20.5 minutes.

Like other swifts of the genus, Cypseloides rutilus is characteristically absent from the nest for extended periods of time particularly after brooding had ended. The feeding intervals of C. rutilus are irregular and lengthy. The one interval for which an exact time was obtained was 36 minutes. All other intervals recorded were in excess of 100 minutes, although the exact duration was not determined.

81







82

The best studied species of Cypseloides, C. niger, may

leave the nest at dawn and not return to feed the nestling until nearly dusk (Smith, 1928). Some feedings have been observed in the morning hours and indicate higher feeding rates at some times, possibly when the nestling is very young. Occasionally, an adult of this species has been observed to feed the nestling, brood it, and then regurgitate a second meal for the young swift several hours after the initial feeding (Michael, 1927). Two adults collected at night at their roosts still had large amounts of food in their throats, which would have enabled them to feed the nestling a second time (Collins, unpubl.).

The most complete information is that for Apus affinis in Kenya (Moreau, 1942b). This swift fed the young birds at intervals ranging from less than 8 to 254 minutes but averaged one feeding trip every 118 minutes for a brood of two. Broods of one were fed at a slower rate and broods of three at a significantly faster rate than either the broods of one or two. Despite acceleration of feeding rate with increased brood size, the rate per individual nestling decreased in larger broods.

In many species a flurry of feeding activity begins shortly before evening roosting, with the adults making many trips to the nest in a short period of time. Both Fischer (1958) and Sherman (1952), however, found that C. pelagica brought smaller quantities of food per trip during such visits, occasionally only a single insect.

An increase in rate of feeding with increasing age of

the nestlings is indicated in some swifts (Kendeigh, 1952t97-98).






83


This is particularly true in times of good weather and an

abundance of food, when the young swifts tend to build up large reserves of subcutaneous fat. Lack (1956c) noticed a tendency for adults to stay away from the nest for longer periods when the young were well fed and consequently did not beg as enthusiastically when adults returned with food.















MOLT


The pattern of molt in both C. brachyura and C. rutilus is similar and is in agreement with the general sequence of molt outlined for species of Chaetura (Snow, 1962). The annual molt starts with the primaries, which are replaced in sequence from

the innermost outward. The secondaries begin to be replaced after the primary molt is well advanced. The replacement of the tail is centripetal and begins after the wing molt has reached about the fourth or fifth primary. Body molt begins soon after the start of the primary molt and spans the whole duration of the molting period. It starts in the head and neck regions and progresses posteriorly over the body, a bit more rapidly on the dorsum than on the venter.

Juvenile birds do not molt either remiges or rectrices during the first fall. Some light body molt was observed in these birds during late September and October which may represent a partial postjuvenal molt of the body feathers.













84
















PARASITES AND PREDATORS


Ectoparasites in the form of mites (Acarina) and

feather lice (Mallophaga) were collected from both species. Mallophagans were particularly abundant on nestlings during the period when their feathers were first emerging from the sheath. Mallophagan eggs were most abundant on the dorsal feathering of the head and neck. Mites were noticed only on the feathers of the wings, particularly on the vanes of the outer primaries. Although these collections have not yet been identified, the

mallophagan species Dennyus brevicapitis has been reported from C. brachyura in Trinidad, and Dennyus brunneitorques and Eureum yepezi from C. rutilus in other parts of its range (Carriker, 1954, 1958).

One specimen of a flea, Polygenis dunni, was caught on a young nestling of C. brachyura. This species has previously been collected from several rodents in Trinidad and northern

South America (Johnson, 1957).

The only endoparasites observed were tapeworms (Taenia sp.) collected from the intestines of both swifts.

Adult mortality in swifts is generally lower than in smaller and slower-flying species of passerines (Lack, 1954). No predators of adult swifts were observed during this study. In Venezuela, Beebe (1950) noted a pair of nesting bat falcons 85






86


(Falco rufigularis) preying heavily on swifts, particularly the smaller species including C. brachyura and C. rutilus.
















DISCUSSION


In their general biology Chaetura brachyura and

Cypseloides rutilus appear similar to most swifts for which information is available. They are almost exclusively aerial in their activities and feed on air-borne arthropods, mostly insects.

The breeding season of both swifts coincides with the

abundance of aerial food associated with the summer rainy season. Many other species of Trinidadian birds have similarly altered

their reproductive cycles so that breeding occurs at a time of maximal abundance of suitable food. For the swallows, as for the swifts, the peak in breeding and the maximal abundance of food both occur early in the rainy season. For the nectar feeding hummingbirds and the bananaquit (Coereba flaveola), however, the maximal food abundance and the peak in breeding occurs at the height of the dry season (December-May) at the time when many forest trees and vines are in flower (Snow and Snow, 1964). The absence of a pronounced peak in food abundance may result in

an extended breeding season as in two species of thrushes (Snow and Snow, 1963). Beyond the tropics, a similar adaptive relationship often exists between breeding season and maximal food abundance, as in temperate zone tits of the genus Parus and arctic sandpipers of the genus Calidris (Gibb, 1954; Holmes, 1966).

87






88


The pattern of nestling growth in both species is

typical of altricial birds, although greatly prolonged as compared to the several small passerines reviewed by Maher (1964). Snow (1962) suggests that the inaccessibility of the nest has caused a relaxation of selection for the accelerated growth of nestlings so typical of most passerine birds nesting in the open.

Chaetura brachyura shows a pronounced similarity in all

aspects of its biology to all other New World species of Chaetura that have been studied. In nest form, clutch size, nestling

growth pattern, feeding habits, and general behavior only minor specific differences exist. For the most part these result from the timing of events during development rather than being major departures from the common pattern. This general similarity is shown by an array of species which inhabit the area from temperate North America south to subequatorial South America, and also includes both sedentary and migratory species.

An equal degree of similarity exists between Cypseloides

rutilus and other congeneric species, although the little information available relates mainly to C. niger.

Although both species studied show similarities to various congeners, several pronounced intergeneric differences occur in their reproductive activities. The nest site of C. rutilus is colder and darker than that of C. brachyura. It is also less accessible to predators and there are reduced losses of both eggs and nestlings of C. rutilus. At the same time this environment imposes several demands upon these swifts as a part of the young. The newly hatched young swift has a very poorly developed






89


capacity for temperature regulation, which improves slowly during the first weeks of nestling life. If left unbrooded in the cold environment of the nest, C. rutilus nestlings would rapidly lose heat to the environment, and much of the energy available for growth would be expended in wasteful thermogenesis.

To prevent such energy-draining heat loss, the adults brood the nestlings until their capacity for thermoregulation has reached a stage where the amount of heat lost without brooding will no longer appreciably slow further growth and development. In C. rutilus and other congeners the development of thermoregulation

is aided by the early appearance of an insulating feather coat. This insulation includes the normal contour feathers, which break out of the sheath at an early date, as well as a down-like semiplume portion of the first teleoptile plumage, which also grows in rapidly. Thus the intergeneric differences in nestling development and adult behavior represent adaptations that enable C. rutilus and other species of Cypseloides to contend with the cold environment of the nest site.

The regulation of clutch size in birds has been studied

in diverse taxa in many parts of the world. The most complete information is based on studies of temperate passerine species in

which the clutch size "has been adapted by natural selection to correspond with the largest number of young for which the parents can, on the average, provide enough food" (Lack, 1954:31).

Studies on Old World temperate and tropical swifts have shown these birds to be similarly food limited with their clutch size adapted to the number of young which can be raised under average






90


conditions (Lack and Lack, 1951; Lack and Am, 1947; Perrins, 1964; Moreau, 1941, 1942a, 1942b). There seems to be no reason to doubt that other swifts in both temperate and tropical parts of the New World are similarly food limited and have their clutch size regulated by the same factors.

As shown in this study, clutch size of C. brachyura

resembles that of other species of Chaetura and is nearly double the clutch size of Cypseloides rutilus. It would thus seem that in Trinidad C. rutilus is capable of obtaining enough food to nourish only two young, while C. brachyura can gather nearly double that amount. As noted earlier only a partial overlap of the feeding range of these swifts occurs with C. rutilus feeding at higher elevations and also at higher altitudes. Even so, it

is hard to accept the view that the food decreases in abundance by nearly 50 per cent with such shifts in feeding ecology and

hence is entirely responsible for the reduction of clutch size in C. rutilus. It is equally hard to accept that C. rutilus is only half as efficient at food gathering as C. brachyura. As noted earlier, however, C. rutilus broods the young more continuously and for a longer time than C. brachyura in order to contend with the cold environment of its nest site. At such times C. rutilus reduces the food supply available to its young by reason of the restriction of foraging to but one adult at a time. The absolute abundance of food may be the same or only slightly diminished in its foraging range, but the effective food supply available to the nestlings is much less. The combination of such reduction in effective food supply, mainly through reduced foraging capacity,






91


could be responsible for the smaller clutch size observed for C. rutilus.

In other species of Cypseloides a clutch size of two is typical, with the exception of C. niger. This species, which nests in extremely cold environments at high elevations in the temperate zone, also has to contend with a less dependable food supply owing to prolonged periods of bad weather in its breeding area. Like other swifts facing similar conditions it shows a further reduction in clutch size, namely to a single egg. It would be interesting to know what the clutch size of this bird is when nesting in less rigorous environments as in parts of

Central America.

Snow (1962) suggested that the small size of C. rutilus nests provides room for only two nestlings with consequent selection for a clutch of only two. This seems doubtful unless

a maximum nest ai~ for Cypseloides can be demonstrated. It also seems unlikely since Cypseloides semicollaris builds no nest and lays only two eggs (Rowley and Orr, 1962).

In their feeding, C. brachyura and C. rutilus apparently select food items within the same range of sizes, but forage in slightly different areas. This may well represent an efficient mechanism to avoid interspecific competition between similarly sized swifts. As noted earlier, differently sized swifts tend to select different sizes of prey items. Thus where two differently sized species share a foraging range the size differences in the food items selected may be sufficient to avoid interspecific food competition. In support of this hypothesis it would be






92


extremely valuable to know the range in size of prey items selected by an extremely large species as Cypseloides

semicollaris or C. zonaris, and any of the tiny species ofCollocalia or Micropanyptila furcata Sutton.

Feeding at higher altitudes above the ground may also represent an adaptive divergence of foraging behavior that further reduces interspecific competition within any given foraging range. In addition to C. rutilus and P. cayennensis, which exhibit this habit in Trinidad, Collocalia maxima Hume similarly forages at higher altitudes and specializes on the larger higher-flying insects in Malaysia (Medway, 1962a). It thereby reduced interspecific competition with the several other Malaysian species of Collocalia.















SUMMARY


The comparative biology of the short-tailed swift,

Chaetura brachyura, and the chestnut-collared swift, Cypseloides

rutilus, was studied in Trinidad during parts of 1962-1964. In many respects both species were similar to congeners for which information exists.

Both swifts breed during the rainy season when insect food is abundant, but their breeding activities are triggered by different proximate factors.

C. brachyura lays a clutch averaging 3.8 eggs in nests of twigs cemented to the walls of manholes. C. rutilus, which lays a clutch of 2 eggs, builds nests of mosses, lycopsids, and ferns on rocky outcrops over rivers and mountain streams, and occasionally in sea caves. The environmental temperature of nest sites of C. rutilus is lower than for those of C. brachyura, and the nestlings of C. rutilus are brooded longer and more continuously than nestlings of C. brachyura. C. rutilus has a lower mortality of eggs and young than C. brachyura, the nest sites of C. rutilus being, presumably, less accessible to predators.

The young of C. brachyura grow more rapidly than those of C. rutilus, but both species perfect their capacity for thermoregulation at about the same rate. In C. rutilus, however,

93






94


a down-like semiplume portion of its first teleoptile plumage emerges at an early age and aids in thermoregulation.

The young of C. brachyura leave the nest when about 3

weeks old and hang on the walls of the nest cavity until fledging at the age of 4-5 weeks. C. rutilus young remain in the nest until fledging at an age of 5-6 weeks.

These two swifts appear to feed on the same types and sizes of aerial food. Their foraging ranges, however, only partially overlap. C. rutilus feeds at higher elevations than C. brachyura and to some extent also at higher altitudes. The differences in foraging ranges may be an adaptation enabling them to avoid interspecific competition for food. Similar adaptations seem to be present in other species of swifts.

Most of the differences in the biology of these two

species of swifts are associated with reproduction and represent adaptations of C. rutilus to the cool, damp environment of the nest site.




Full Text
AGE IN DAYS
Fig. 14. Decrease in body temperature of nestling swifts under cold stress.
Vertical line represents the range, and rectangles two standard errors on
either side of the mean.


92
extremely valuable to know the range in size of prey items
selected by an extremely large species as Cypseloides
semicollaris or C. zonaris, and any of the tiny species of -
Collocalia or Micropanyptila furcata Sutton.
Feeding at higher altitudes above the ground may also
represent an adaptive divergence of foraging behavior that
further reduces interspecific competition within any given
foraging range. In addition to C. rutilus and P. cayennensis,
which exhibit this habit in Trinidad, Collocalia maxima Hume
similarly forages at higher altitudes and specializes on the
larger higher-flying insects in Malaysia (Medway, 1962a). It
thereby reduced interspecific competition with the several
other Malaysian species of Collocalia.


17
as much as 10 feet down where they often received direct sun
light for part of the day. Nests were occasionally re-used
in successive years but in most cases they peeled off the wall
soon after the nesting season. Before re-use additional twigs
appeared to be added to the nest, as has been recorded for C.
pelgica (Amadon, 1936; Fischer, 1958). In but a few cases did
C. brachyura build up the semicircular arch of saliva on the
wall above the nest so diagnostic of C. pelgica nests (Fischer,
1958; Fig. 8). The absence of this additional support may
account for the more rapid destruction of C. brachyura nests.
Egg laying starts about 10 days after the beginning of con
struction and before the nest is completely finished. The
nests are unlined, but in two cases a feather was found glued
in among the sticks, and a large white feather was once found
in the bottom of a nest containing recently hatched young.
A variety of other organisms were also found in the
manhole nest sites. Those holes that were partially filled
with water usually contained the tree frog Hyla rubra. An
unidentified snake and a lizard, Ameiva ameiva, were each seen
on one occasion at the bottom of dry holes, presumably having
gotten there through the connecting drainage pipe. Wet and
dry holes alike often contained one or more nests of the "Jack
Spaniard" or paper wasp (Polistes canadensis), under the over
hanging edge of the top and the globular mud nest of the potter
wasp (Eumenes canaliculatus), on the walls. Spiders of several
types frequented the manholes, and on one occasion Snow (1962)
observed a large spider (Mygale sp.) pounce on and kill a


86
(Falco rufigularis) preying heavily on swifts, particularly
the smaller species including C. brachyura and C. rutilus.


STUDY AREA
The William Beebe Tropical Research Station of the
New York Zoological Society in Arima Valley, Trinidad, formed
the base of operations for this study. The station, located
four miles north of the town of Arima, is at an elevation of
800 feet and provides an excellent vantage point from which to
observe feeding swifts, as well as being close to nesting con
centrations of both species. The present study included approxi
mately eleven months of field work in Trinidad during part or
all of the breeding seasons of 1962-1964, exact dates being
26 June-1 Sept. 1962; 25 April-11 July 1963; 8 May-11 Nov.
1964.
The ecology of Arima Valley has been described in some
detail by Beebe (1952), and the best description of the vege
tation types in Trinidad is that by Beard (1946).
Field observations were concentrated in the eastern
half of St. George County and included areas of low country
savanna, upper montane rain forest at elevations of 2500 to
3000 feet, and the rocky coastline of the north shore of the
island. Hie principal nesting area for C. brachyura was Waller
Field, a United States Air Force base deserted for more than
ten years and heavily overgrown except for the roads and a few
cement structures. Most nests of C. rutilus were located in
3


36
Four two-day-old young and two eggs were in the nest on 2 June,
after an incubation period of approximately 17 days. The re
maining two eggs hatched on 6 and 7 June and both of the newly
hatched young birds were found later the same day dead or nearly
dead on the floor of the nest cavity. Presumably they were
inadvertently shoved out of the nest by the movements of the
older and stronger nestlings. An evening check of this nest
showed three adults roosting together near the nest; one of them
was known to be a yearling bird raised in that nest cavity the
preceding year.
Two females trying to lay in the same nest may have
caused disruption of egg laying and ejection of eggs in two
other cases. Adult birds were frequently observed roosting
in nest cavities with a nesting pair, although not in close
approximation. At three additional nests extraparental coopera
tion was observed in the feeding of the young.
In C. pelgica extraparental cooperation occurs regu
larly and may involve birds of all ages and both sexes includ
ing young of the previous year. These helpers share in the
incubation and brooding duties as well as the feeding of the
young (Dexter, 1952). Further observations with individually
marked birds might well show it to be of regular occurrence
in C. brachyura. The cause of such extraparental cooperation
in Chaetura is not yet clear. It may be due to a shortage of
nest sites as suggested by Snow (1962), or to the inability of
some birds to find mates as suggested by Dexter (1952). Skutch
(1961) feels that such activities in passerine birds may


101
Perrins, Christopher
1964. Survival of young swifts in relation to brood size.
Nature, 201:1147-1148.
Rathbun, S. F.
1925. The black swift and its habits. Auk, 42:497-516.
Reboratti, J. H.
1918. Nidos y huevos de vencejos. Homero, 1:193.
(reference from Lack, 1956)
Rowley, J. Stuart, and Robert T. Orr
1962.
1965.
Schmidt,
1965.
Sherman,
1952.
Sick, H.
1948a.
1948b.
1959.
Sims, R.
1961.
Skutch,
1961.
The nesting of the white-naped swift. Condor, 64:
361-367.
Nesting and feeding habits of the white-collared swift.
Condor, 67:449-456.
Rudolf K.
Brutbiologie des weiss Burzelseglers Apus caffer caffer
(Lichtenstein) auf der Kaphalbinsel. Joum. f. Ornith.
106:295-306.
Althea R.
Birds of an Iowa Doryard. Ihe Christopher Pub. House,
Boston. 270 pp.
The nest of Chaetura andrei meridionalis. Auk., 65:
515-520.
The nesting of Reinarda squamata (cassin). Auk., 65:
169-174.
Notes on the biology of two Brazilian swifts, Chaetura
andrei and Chaetura cinereiventris. Auk., 76:471-477.
W.
The identification of Malaysian species of swiftlets
Collocalia. Ibis, 103a:205-210.
Alexander F.
Helpers among birds. Condor, 63:198-226.


23
added annually, with several distinct layers representing the
annual additions. Sea cave nests of C. rutilus appeared to be
constructed of slightly different materials and may well have
contained seaweed as reported for a similarly located nest of
C. niger (Legg, 1956).
C. rutilus nests have been found on rocky outcrops
overhanging pools in mountain streams (Fig. 6), on the rocky
walls of a river gorge, in sea caves, and also in man-made
culverts (Fig. 4a) and in one case on the underside of a bridge
(Belcher and Smooker, 1936; Snow, 1962). In general the sites
are similar to those for other species of Cypseloides in being
in deep shadow, inaccessible to terrestrial animals, and closely
associated with water. They do not strictly agree with the
ecological "requirements" outlined for C. niger in that they
are rarely associated with high relief. All nests of this
species have been found in forested areas at localities of
relatively low elevations from sea. level to 1100 feet. Most
nests were in deep shadow and none received direct sunlight.
Streamside nests were only 2-4 feet above the water, but nests
in a gorge were as much as 25 feet above the river, although
still in a damp situation owing to seepage water on the walls.
The sea-cave nests were about 6-8 feet above either permanent
water or tidal wash.
In contrast with the larger species C. zonaris and C.
niger, which nest near, and sometimes behind, waterfalls, only
one C. rutilus nest was near falling water. This nest was on
a smooth wall about 8 feet above a pool of water, into which


53
figures show that C. brachyura has an initially higher average
daily weight gain and average per cent growth rate that sub
sequently decline rapidly. After approximately three weeks of
nestling life the young begin to los weight, particularly when
they first leave the nest and again later when they begin to
fly. C. rutilus, on the other hand, has an initially lower
average daily weight gain and average percent growth rate which
also declines although at a slower rate so that the nestlings do
not begin to lose weight until late in the nestling period
approximately 4 1/2 weeks after hatching.
The general pattern of growth shown by these two swifts
is similar to those reported for most altricial birds, particu
larly those with longer periods of development (Dawson and Evans,
1957, 1960; Maher, 1964; Kahl, 1958). identical in growth pattern to C. pelgica and C. vauxi, the
only previously studied species of Chaetura (Fischer, 1958;
Baldwin and Zaczkowski, 1963). C. rutilus is most similar in
growth pattern to European species in the genus Apus with
similarly long fledging periods (Lack and Lack, 1951; Weit-
nauer, 1947). No information is available for any other
Cypseloides species.
General development
Feathers. Like other species of swifts, C. brachyura
C. rutilus are hatched naked. Approximately 4 days after
hatching the developing contour feathers appear under the skin
as dark dots along the feather tracts. The remiges are first


MOLT
The pattern of molt in both C. brachyura and C. rutilus
is similar and is in agreement with the general sequence of molt
outlined for species of Chaetura (Snow, 1962)* The annual molt
starts with the primaries, which are replaced in sequence from
the innermost outward. The secondaries begin to be replaced
after the primary molt is well advanced. The replacement of the
tail is centripetal and begins after the wing molt has reached
about the fourth or fifth primary. Body molt begins soon after
the start of the primary molt and spans the whole duration of
the molting period. It starts in the head and neck regions and
progresses posteriorly over the body, a bit more rapidly on the
dorsum than on the venter.
Juvenile birds do not molt either remiges or rectrices
during the first fall. Some light body molt was observed in
these birds during late September and October which may repre
sent a partial postjuvenal molt of the body feathers.
84


BROODING
Until they are about two weeks old, nestlings of both
swift species are brooded at night by one or both parents. By
this time the young are too large to be covered by the adults.
During the first days of their life nestlings of C. brachyura
are regularly brooded for long daytime periods, and for shorter
periods, of 20 minutes duration or less, as late as 8 days after
hatching. As early as the second day after hatching, however,
both adults are sometimes absent, presumably foraging for the
young. Nestlings of C. rutilus usually are continuously brooded
during the daytime for the first 10-11 days, and occasionally as
late as 13 days after hatching.
Most species of swifts brood during the daytime for
most of the first week of nestling life, although both adults
may be absent for short periods, particularly around dusk.
Thereafter, daytime brooding is sporadic and highly variable in
duration. In England, daytime brooding was recorded in Apus
apus for 98 per cent of the time during the first week of nest
ling life, up to 52 per cent during the second week, and 7 per
cent or less thereafter.
44


31
Table 3. Distribution of Cypseloides rutilus nests in half-
month intervals
Period
1957*
1958*
1958*
1960*
1
1961*
1962
1963
1964
All
Years
1 -15 April
16-30 April
1
1
1-15 May
1
1
1
3
16-31 May
1
1
2
1
5
6
16
1 -15 June
1
1
2
3
5
1
13
16-30 June
1
2
1
2
6
1 -15 July
2
1
3
16-31 July
2
1
2
1
2
**
8
1 -15 Aug.
1
1
1
2
1
1
**
4
11
16-31 Aug.
1
3
2
**
2
8
Total
2
9
7
8
9
11
10
13
69
Data from Snow (1962)
No observations


THE COMPARATIVE BIOLOGY
OF TWO SPECIES OF SWIFTS IN
TRINIDAD, W. I.
By
CHARLES THOMPSON COLLINS
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
June, 1966


TAIL LENGTH IN MM
Fig. 10. Growth of the tail of Chaetura brachyura and Cypseloides rutilus.
Vertical lines represent ranges, curves connect daily means.
Ul
o


73
the large flights of winged reproductive termites. Feeding on
this temporary plethora of food was not confined to the swifts.
Numerous species, ranging in size from house wrens (Troglodytes
aedon) to caciques (Psarocolius decumanus), also preyed on them.
A similar array of birds was noted feeding on termite swarms
in Panama (Eisenmann, 1961). On several occasions I observed
Chaetura brachyura to bank sharply up and flutter briefly near
the outermost branches of trees extending above the forest
canopy. It appeared that the birds were picking insects or
spiders off the leaves. Similar foraging behavior was noticed
for C. pelgica (Fischer, 1958) and may be widespread among
swifts.
Other swifts have been observed feeding in several less
typical ways. Apus apus has been noticed landing on the wall
of a house and gathering spiders under the eaves (Meikeljohn,
1928), and foraging for insects and perhaps nest parasites in
old swallow nests (Gilbert, 1944).
The stomach contents of the swifts collected during this
study were mostly masses of partially digested, poorly identifiable
insect remains. On the other hand, the food brought to the nest
lings was easily identified and probably consisted of the same
food consumed by the adults. The adults brought the food for
the young swifts to the nest in their throat as a compact mass
of undigested insects partially glued together by saliva. A
total of 21 samples of the food brought to nestlings was collected,
17 from C. brachyura and 4 from C. rutilus. These samples were
manipulated from the throat of recently fed nestlings. This


43
rutilus have been seen on occasion to exercise their wings while
"hanging to the outer rim of the nest" (Snow, 1962). Any attempts
to clamber about on the rocky walls adjoining the nest would
probably result in death, as these surfaces are usually smooth
and often wet and slippery.
The combined nestling-fledgling periods for most swifts
are between 35-45 days, with larger species requiring slightly
longer than smaller ones. Usually short periods of 29-32 days
were noted for Cypsiurus parvus (Lichtenstein) and 30 days for
Chaetura pelgica (Moreau, 1941; Fischer, 1958). Slight geo
graphic variation in the nestling-fledgling period has been noted
in Apus caffer (Lichtenstein), which averages 42 days in Kenya
and 46 days in South Africa (Moreau, 1942a; Schmidt, 1965).
Weather conditions can also affect the length of this period,
bad weather extending it as much as two days (Lack, 1956b).


91
could be responsible for the smaller clutch size observed for
C. rutilus.
In other species of Cypseloides a clutch size of two is
typical, with the exception of C. niger. This species, which
nests in extremely cold environments at high elevations in the
temperate zone, also has to contend with a less dependable food
supply owing to prolonged periods of bad weather in its breeding
area. Like other swifts facing similar conditions it shows a
further reduction in clutch size, namely to a single egg. It
would be interesting to know what the clutch size of this bird
is when nesting in less rigorous environments as in parts of
Central America.
Snow (1962) suggested that the small size of C. rutilus
nests provides room for only two nestlings with consequent
selection for a clutch of only two. This seems doubtful unless
a maximum ne§t sis for Cypselaldas can be demonstrated. It
also seems unlikely since Cypseloides semicollaris builds no
nest and lays only two eggs (Rowley and Orr, 1962).
In their feeding, C. brachyura and C. rutilus apparently
select food items within the same range of sizes, but forage
in slightly different areas. This may well represent an efficient
mechanism to avoid interspecific competition between similarly
sized swifts. As noted earlier, differently sized swifts tend
to select different sizes of prey items. Thus where two dif
ferently sized species share a foraging range the size differences
in the food items selected may be sufficient to avoid interspecific
food competition. In support of this hypothesis it would be


2
nine species of Trinidadian swifts. These two species, the
short-tailed swift, Chaetura brachyura (Jardine), and the
chestnut-collared swift, Cypseloides rutilus (Vieillot), are
approximately the same size but have striking differences in
nesting ecology, clutch size, and the development of the young.
The present study was undertaken, therefore, to analyze these
differences and, when possible, to point out their adaptive
significance.
Differences in nest type have been shown to be useful
characters in differentiating species of swiftlets of the genus
Collocalia (Sims, 1961; Medway, 1961), while differences in
ecology and clutch size appear to be significant indicators
of higher intrafamilial relationships (Lack, 1956a). Thus
the study of the comparative ecology of additional species,
in conjunction with studies of the anatomy, osteology, and
paleontology of swifts, should provide knowledge useful in
understanding the evolution of the Apodidae.


7
Fig. 1. Cold chamber used in tests of thermoregulatory
capacity of nesting swifts.


83
This is particularly true in times of good weather and an
abundance of food, when the young swifts tend to build up large
reserves of subcutaneous fat. Lack (1956c) noticed a tendency
for adults to stay away from the nest for longer periods when
the young were well fed and consequently did not beg as en
thusiastically when adults returned with food.


67
In most cases these young were dead or missing from the nest
at the next visit. The capacity for dropping into torpor may
exist in all swifts, but it does not appear to be utilized in
the normal course of events by either C. brachyura or C. rutilus.


This dissertation was prepared under the direction of
the chairman of the candidates supervisory committee and has been
approved by all members of that committee. It was submitted to
the Dean of the College of Arts and Sciences and to the Graduate
Council, and was approved as partial fulfillment of the require
ments for the degree of Doctor of Philosophy.
June 21, 1966
Dean,
Supervisory Committees
Rehuir
Dean, Graduate School


SUMMARY
The comparative biology of the short-tailed swift,
Chaetura brachyura, and the chestnut-collared swift, Cypseloides
rutilus, was studied in Trinidad during parts of 1962-1964. In
many respects both species were similar to congeners for which
information exists.
Both swifts breed during the rainy season when insect
food is abundant, but their breeding activities are triggered
by different proximate factors.
C. brachyura lays a clutch averaging 3.8 eggs in nests
of twigs cemented to the walls of manholes. C. rutilus, which
lays a clutch of 2 eggs, builds nests of mosses, lycopsids, and
ferns on rocky outcrops over rivers and mountain streams, and
occasionally in sea caves. The environmental temperature of nest
sites of C. rutilus is lower than for those of C. brachyura,
and the nestlings of C. rutilus are brooded longer and more
continuously than nestlings of C. brachyura. C. rutilus has
a lower mortality of eggs and young than C. brachyura, the nest
sites of C. rutilus being, presumably, less accessible to preda
tors.
The young of C. brachyura grow more rapidly than those
of C. rutilus, but both species perfect their capacity for
thermoregulation at about the same rate. In C. rutilus, however,
93


28
and Disney, 1956; Miller, 1959). However, the small annual
change in photoperiod at the lower latitudes makes it reasonable
to assume that these swifts and possibly other tropical birds
respond to a combination of photoperiod and some more variable
environmental stimulus similar to the situation in the erratically
breeding red crossbill, Loxia curivostra, of the temperate zone.
This crossbill shows only a partial response to increasing or
constant long photoperiods. The completion of gonadal develop
ment and the triggering of breeding is dependent upon some
proximate environmental factor as an increased availability of
suitable food (Tordoff and Dawson, 1965).
The most obvious environmental factor potentially
regulating the breeding of these Trinidadian swifts is the
onset of the annual rainy season. Even so, the response of
each of these two species is somewhat different. C. brachyura
usually begins nesting before C. rutilus and very soon after
the first heavy rains of the season. The first sign of breed
ing activity is the appearance of new nests or in some cases
the addition of new material to old nests. These activities
coincide with the start of the summer rainy season, and in
those years when brief heavy rains precede the period of intense
summer rainfall, C. brachyura often begins nesting at an earlier
date. For example, in 1959, there were heavy rains early in
April followed by a dry spell until the beginning of the true
summer rains in the middle of May. Ihis false start triggered
breeding by C. brachyura in April followed by a lull during the
dry spell and renewal of nesting activity in late May (Snow,


22
Fig. 5. Nesting material of Cypseloides rutilus growing on
stream-side rock ledge.


GROWTH
Body weight
A total of 321 nestling weights was obtained in the
field, from a total of 57 chicks from 15 nests of C. brachyura
(Fig. 7). From 1-15 weights were obtained from a single nest
ling. A total of 165 weights of C. rutilus nestlings was ob
tained from 25 individuals weighed between 1-16 times each
(Fig. 8).
At hatching the average weight of C. brachyura nest
lings was 1.6 grams and 18 days later it reached a maximum of
21.2 grams, a 13.3-fold increase. At fledging they had reached
approximately 87 per cent of their adult weight.
The average weight of C. rutilus at hatching, was 2.1
grams, and it reached a maximum average weight of 26.2 grams on
day 29, a 12.4-fold increase. At fledging C. rutilus weighed
approximately 119 per cent of the adult weight.
The instantaneous percentage growth rate, calculated
for each day (Brody, 1945: 508), tended to decrease in both
species after an initial rise (Tables 7-8). C. brachyura had
its peak growth rate on the fourth day after hatching: the
similar peak for C. rutilus did not occur until the seventh
day. The average weight gain per day and the average per cent
growth rate per day were calculated for 7 five-day periods
during the nestling life of these two species (Table 9). These
47


80
the most frequent sizes being 9 and 10 mm, or about the maximum
size recorded for either C. brachyura or C. rutilus (Collins,
unpubl.). If extended to other situations, two species of
similar size would expectedly feed on insects within similar
size ranges. The food habits of Apus apus and A. pallidus
(Shelley) support this idea. These two swifts are nearly equal
in size and select similar sized prey items (G. E. Watson, pers.
comm.).


THE COMPARATIVE BIOLOGY
OF TWO SPECIES OF SWIFTS IN
TRINIDAD, W. I.
By
CHARLES THOMPSON COLLINS
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
June, 1966

ACKNOWLEDGMENTS
I extend ray deep appreciation to Pierce Brodkorb for
his valuable supervision of this problem. Sincere thanks are
%
also due to the other biologists who critically read the manu
script: E. G. Franz Sauer, Thomas J. Walker, Brian K. McNab,
and Frank G. Nordlie. I am particularly grateful to David W.
Snow for acquainting me with these swifts and their nest sites
and for making his notes available to me. Miss Jocelyn Crane
and the Department of Tropical Research of the New York Zoologi
cal Society greatly facilitated my field work in Trinidad.
Thanks are also due Mrs. H. Newcomb Wright, Spring Hill Estate,
Arima Valley, Trinidad, for her hospitality and permission to
study the swifts nesting there. I wish to gratefully acknowledge
the financial support for this study received from the Frank
M. Chapman Memorial Fund of the American Museum of Natural
History in 1962 and 1963, and in 1964 the National Science
Foundation (Summer Fellowship for Graduate Teaching Assistants)
and Cyril K. Collins.
To John Beckner who identified the nest materials, and
to John F. Anderson, Frank M. Mead, Thomas E. Snyder, Phyllis
T. Johnson, and Robert E. Woodruff, who identified the arthropods,
I am also grateful.
XX

TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS i i
LIST OF TABLES v
LIST OF ILLUSTRATIONS vi
INTRODUCTION 1
STUDY AREA 3
METHODS AND MATERIALS 5
GENERAL DESCRIPTION 8
RANGE 10
NESTS AND NEST SITES 11
Chaetura brachyura 11
Cypseloides rutilus ............. 18
BREEDING SEASONS 27
CLUTCH SIZE 33
INCUBATION
PARENTAL CARE 41
Chaetura brachyura 41
Nestling period. ..... .. 41
Fledgling period 41
Cypseloides rutilus ........... 42
BROODING 44
FLEDGING SUCCESS 45
GROWTH
Body weight 47
iii

General development 53
Feathers 53
Eyes 58
Bill and feet 58
Behavior 61
Development of horneothermy 62
Torpor 66
ADULT WEIGHT 68
FOOD AND FEEDING HABITS 70
FEEDING OF YOUNG 81
MOLT 84
PARASITES AND PREDATORS 85
DISCUSSION 87
SUMMARY 93
LITERATURE CITED 95
BIOGRAPHICAL SKETCH 103
IV

LIST OF TABLES
Table Page
1. Nest dimensions of swifts of the genus Chaetura. 16
2. Distribution of Chaetura brachyura nests in half
month intervals. 30
3. Distribution of Cypseloides rutilus nests in half
month intervals 31
4. Distribution of clutch sizes of Chaetura brachyura
by half-month intervals for years 1962 to 1964 34
5. Clutch size of swift species in the genus Chaetura 35
6. Average hatching and fledging success of swift
species 39
7. Daily weight (grams) and relative growth rate
(per cent) of Chaetura brachyura 50
8. Daily weight (grams) and relative growth rate
(per cent) of Cypseloides rutilus 51
9. Average daily growth rate (grams) and relative
growth rate (per cent) for five-day intervals for
Chaetura brachyura and Cypseloides rutilus .... 52
10.Contents of food balls collected from nestlings
of Chaetura brachyura and Cypseloides rutilus. 75
v

LIST OF ILLUSTRATIONS
Figure Page
1. Cold chamber used in tests of thermoregulatory
capacity of nestling swifts. .. ... 7
2. Manhole nest sites of Chaetura brachyura 13
3. Nests of Chaetura brachyura 15
4. Nests of Cypseloides rutilus ..... 20
5. Nesting material of Cypseloides rutilus growing
on stream-side rock ledge 22
6. Stream nesting habitat of Cypseloides rutilus. 24
7. Growth curve of Chaetura brachyura ........ 48
8. Growth curve of Cypseloides rutilus 49
9. Growth of the wing of Chaetura brachyura and
Cypseloides rutilus 55
10. Growth of the tail of Chaetura brachyura and
Cypseloides rutilus. ............... 56
11. Chaetura brachyura nestlings and fledglings. ... 60
12. Body temperatures of nestlings of Chaetura
brachyura when unbrooded 63
13. Body temperatures of nestlings of Cypseloides
rutilus when unbrooded ...... 64
14. Decrease in body temperature of nestling swifts
under cold stress. 65
15. Size of prey selected by Chaetura brachyura and
Cypseloides rutilus. ............... 79
vi

INTRODUCTION
Swifts of the family Apodidae form a well-defined group
of streamlined, fast-flying birds which spend most of the day
light hours on the wing in pursuit of their insect prey. They
occur throughout the world but are most abundant in tropical
regions. Although the biology of swifts has been studied in
Africa (Moreau, 1941, 1942a, 1942b), South America (Sick,
1948a, 1948b, 1959) and Malaysia (Medway, 1962a, 1962b), the
family as a whole is still poorly known. The nests of several
species have only recently been discovered (Rowley and Orr,
1962) and others are undescribed. A new species remained un
detected in a well studied part of northwestern South America
as late as 1962 (Eisenmann and Lehmann, 1962). The difficulty
of locating swift nests, which are usually solitary and often
in inaccessible cliff crevasses or in hollow trees, has clearly
hindered the study of additional species, particularly in the
tropics. At present, detailed life history data are confined
for the most part to a few species of the temperate zone (Lack
and Lack, 1951, 1952; Weitnauer, 1947; Fischer, 1958).
The island of Trinidad, having probably the largest
swift fauna for an area its size, offers abundant opportunities
for ecological studies. The preliminary work by Snow (1962) in
dicated the practicality of a detailed comparison of two of the
1

2
nine species of Trinidadian swifts. These two species, the
short-tailed swift, Chaetura brachyura (Jardine), and the
chestnut-collared swift, Cypseloides rutilus (Vieillot), are
approximately the same size but have striking differences in
nesting ecology, clutch size, and the development of the young.
The present study was undertaken, therefore, to analyze these
differences and, when possible, to point out their adaptive
significance.
Differences in nest type have been shown to be useful
characters in differentiating species of swiftlets of the genus
Collocalia (Sims, 1961; Medway, 1961), while differences in
ecology and clutch size appear to be significant indicators
of higher intrafamilial relationships (Lack, 1956a). Thus
the study of the comparative ecology of additional species,
in conjunction with studies of the anatomy, osteology, and
paleontology of swifts, should provide knowledge useful in
understanding the evolution of the Apodidae.

STUDY AREA
The William Beebe Tropical Research Station of the
New York Zoological Society in Arima Valley, Trinidad, formed
the base of operations for this study. The station, located
four miles north of the town of Arima, is at an elevation of
800 feet and provides an excellent vantage point from which to
observe feeding swifts, as well as being close to nesting con
centrations of both species. The present study included approxi
mately eleven months of field work in Trinidad during part or
all of the breeding seasons of 1962-1964, exact dates being
26 June-1 Sept. 1962; 25 April-11 July 1963; 8 May-11 Nov.
1964.
The ecology of Arima Valley has been described in some
detail by Beebe (1952), and the best description of the vege
tation types in Trinidad is that by Beard (1946).
Field observations were concentrated in the eastern
half of St. George County and included areas of low country
savanna, upper montane rain forest at elevations of 2500 to
3000 feet, and the rocky coastline of the north shore of the
island. Hie principal nesting area for C. brachyura was Waller
Field, a United States Air Force base deserted for more than
ten years and heavily overgrown except for the roads and a few
cement structures. Most nests of C. rutilus were located in
3

4
the northern half of Arima Valley, but a few were in sea
caves on the north coast, particularly near the town of
Blanchisseuse.

METHODS AND MATERIALS
During the nesting season individual nests were checked
regularly, usually once a day or less in order to avoid exces
sive disturbance and possible desertion.
In 1962 adults and nestlings were marked with numbered,
colored plastic bands and, starting in 1963, also with U. S.
Fish and Wildlife Service numbered, aluminum bands. Nestlings
less than 8-10 days old could not be banded and were marked
with spots of color applied with a felt marking pen to the
skin of the back or belly. Color marking of nestlings and
adults was only used to a limited extent. An attempt to color
mark a prebreeding flock of C. brachyura, by painting the pri
maries of one wing yellow, proved unsuccessful as the birds
could not be readily distinguished in the field.
Weights of adults and nestlings were obtained with
spring balance of the type obtainable from the British Trust
for Ornithology. This balance was calibrated in half-gram
intervals, and weights were estimated to the nearest quarter
gram.
Environmental temperatures were obtained by means of
Sixs type maximum-minimum recording thermometers. Body
temperatures were measured with a small bulb mercury ther
mometer made by the Schultheis Corporation. Readings were
5

6
taken with the bulb inserted about 10 mm into the cloaca.
Cold stress experiments were used as a part of the
investigation of nestling thermoregulation. These involved
a 6x8x5 inch cold chamber constructed of 1-1/8 inch thick
foam plastic insulation material (Fig. 1). When equipped with
four 6-oz cans of "Skotch Ice" (refreezable liquid), this
chamber maintained a temperature of approximately 5 C for
several hours. In the field, nestlings were placed individually
in the chamber for a period of 5 minutes, and their temperatures
were recorded before and after cold exposure. Even though
sharp body temperature drops were recorded for very young
nestlings, no ill effects were attributable to this test.
Swifts of both species were yaptured at night roosting
places for weight and molt studies. Flocks of C. brachyura
were generally confined in a roost site and examined the follow
ing morning. A hand net was used to capture C. rutilus adults
roosting in a river gorge in Arima Valley; they were held in
captivity over night and released the following morning.

7
Fig. 1. Cold chamber used in tests of thermoregulatory
capacity of nesting swifts.

GENERAL DESCRIPTION
Chaetura brachyura is one of four similar-appearing
congeneric species that occur in Trinidad. It is a small bird
about 115 mm long with a short stubby tail (28-33 mm) and long
narrow wings (117-127 mm). In fresh plumage it is dark black-
/
brown, except for the rump and under tail coverts which are
pale ashy brown. The throat is slightly paler than the breast.
The feathers of the darker areas, particularly the remiges,
have a noticeable greenish gloss or iridescence. In worn
plumage the gloss is purple or completely bleached out to a
lusterless dark brown, and the bird appears paler, particularly
on the throat, and is more brownish than black. Occasional
individuals have been collected in late summer with extremely
light brown underparts, but the cause of this is not understood.
Birds in juvenal plumage are less glossy on the body areas than
adults and have a more grayish tinge to the paler rump and under
tail areas.
Cypseloides rutilus appears to be a larger swift
(135 mm) owing to its longer tail (38-42 mm), but its wings are
about the same length (119-128 mm) as those of C. brachyura.
In over all color C. rutilus is dark sooty black-brown, darker
on the wings and tail than on the body. The males have a
complete collar of rufous feathers covering the nape, auricular,
8

9
loral and malar regions, but not the interramal areas nor the
throat and upper portion of the breast. The females are
generally uniform dark brown. A few birds have a partial
rufous collar on the nape and extending laterally to the edges
of the throat, with sometimes additional flecks on the throat
and breast. Two such birds were collected and both proved to
be females. Despite numerous statements to the contrary it
is not the juveniles that completely lack the collar. In
fact, birds in juvenal plumage invariably have some rufous
present as a partial collar. The edges of the collar are not
so sharply delimited as in the adults, and the crown feathers
also have narrow reddish edges. The extent of the rufous
coloring in the juvenal plumage is variable, but it is never
so extensive as in adult males nor is it completely lacking
as in most adult females.

RANGE
Chaetura brachyura inhabits the southernmost Lesser
Antilles and northern South America, with a single report in
southern Panama. It is abundant on the islands of St. Vincent,
Trinidad, and Tobago and on the mainland from Venezuela and
Colombia south to Peru and the Matto Grosso of Brazil.
Cypseloides rutilus ranges continuously from southern
Mexico to Peru and Bolivia and east through northern Venezuela
and Trinidad. A separate population also exists in the high
lands of southeastern Venezuela and the neighboring parts of
British Guiana.
10

NESTS AND NEST SITES
Chaetura brachyura
There are relatively few records for nests in natural
settings for most species of Chaetura. The available informa
tion indicates that all tend to utilize hollow trees or stumps
and occasionally affix their bracket-shaped nests to vertical
rocky ledges or the walls of caves (Lack, 1956a). Most species
in the genus have been quick to accept various artificial
equivalents of these natural hollows, and as early as the 1870s
accounts began to appear in journals of their nesting in
numerous man-made structures including chimneys, wells, cis
terns, and a variety of buildings (Lack, 1956a; Fischer, 1958)#
The species most clearly illustrating this habit is the North
American chimney swift, Chaetura pelgica (Linnaeus), which
"now breeds much more often in chimneys than in trees" (Lack,
1956a). Other New World species of Chaetura known to use man
made structures are C. vauxi vauxi (Townsend) in temperate
areas (Baldwin and Hunter, 1963; Baldwin and Zaczkowski, 1963)
and C. vauxi aphanes Wetmore and Phelps, Jr. (Sutton, 1948),
C. andrei Berlepsch and Hartert (Sick, 1959) and C. brachyura
(Haverschmidt, 1958) in tropical South America. In Trinidad
C. brachyura has previously been reported to use chimney and
sea-cave nest sites (Belcher and Smooker, 1936), as well as
11

12
subterranean manholes and a nest box erected for swifts (Snow,
1962).
The C. brachyura nest sites followed in this study were
all in vertical manholes which were part of the underground
drainage system of Waller Field (Fig. 2). Eleven of these
sites were discovered by Snow and kept under observation by him
from May 1957 until September 1961 (Snow, 1962). An additional
ten holes used as nest or roosting sites were found during this
study and observed during 1962-1964. For the most part the
manholes were cylindrical concrete tubes from 4-20 feet deep,
connecting with a smaller lateral drainage pipe at the bottom.
The holes had an inside diameter of about 4-1/2 feet, and
usually had a concrete top pierced by a circular access hole, 2
feet in diameter, which at one time had been closed by a metal
manhole cover. One hole, slightly narrower and made of bricks,
had an uneven surface as opposed to the smooth walls of those
made of concrete. The only site not in one of these holes was
located in a subterranean, concrete-walled room about 20 feet
long, 10 feet wide, and 10 feet high. The swifts entered
and left this room through a 12-inch square opening in the
ceiling, which was flush with the ground level. The tops of
several of the manholes were also flush with the ground;
others protruded as much as 4 feet above ground. One of the
manholes used predominantly as a roosting site was nearly
roofed over with a metal sheet covered by cement, with only a
very small hole, 5-1/2 by 10 inches, providing access for the
swifts. Fourteen of the 21 sites were partially filled with

13
Fig. 2. Manhole nest sites of Chaetura brachyura, Waller Field,
Trinidad.

14
water or had water flowing through the bottom drainage pipe
during the nesting season. In three sites nests were destroyed,
and in one case an adult was trapped by rising water in the
hole. Although the nest sites were usually brightly illuminated
there was very little circulation of air, and the relative
humidity was in excess of 95 per cent at all times. The
temperature in these manholes had a range of from 25.0 to 33.3 C
during the nesting season. A characteristic daily range was
from a low of 26.0 to a high of 30.5 C.
Although nest building was not observed for this species,
the finished nest of C. brachyura is so similar to that of all
other New World species in the genus that the building process
must also be highly similar. The best studied species, C.
pelgica, collects nesting material by grasping tree-top
twig s in its feet and breaking them off while in flight
(Fischer, 1958). The nest is made entirely of such twigs
glued together and affixed to a vertical surface by means of a
secretion of the sublingual salivary glands. C. brachyura
shows a pronounced enlargement of these glands during the
breeding season, as has been reported for C. pelgica (Johnston,
1958) and several species of Collocalia (Medway, 1962c).
The nest of C. brachyura is a shallow half-saucer of
twigs which are 20-75 mm long and usually only 1-2 mm in di
ameter (Fig. 3). It is slightly smaller than the nests de
scribed for other species of Chaetura (Table 1). The nests were
glued to the walls of the manholes at varying heights, some
being near the top where they were in deep shadow and others

15
Fig
3
Nests of Chaetura brachyura

16
Table 1. Nest dimensions of swifts of the genus Chaetura.
(W) width of nest at greatest point along rim, (FB) greatest
distance from back to front rim, (D) greatest depth from rim
to bottom of nest. Measurements in centimeters.
Number
of
nests
Average
Range
C. brachyura
W
6.2
5.4 6.9
FB
8
5.3
4.0 6.5
D
2.5
1.8 3.3
C. pelgica-1-
W
--
7.5 -11.3
FB
?

5.0 7.5
D

2.5 3.1
C. vauxi2
W
10.0

FB
1
6.0

D
4.0
-
C. andrei3
W
8.5
7.5 9.5
FB
3
4.3
3.5 5.0
D
3.7
2.5 3.0
C. chapmani^
W
6.9
FB
1
5.9

D
2.4

-'-Fischer, 1958; Bendire, 1895
2Dickinson, 1951
3Sick, 1959
^Collins, unpub.

17
as much as 10 feet down where they often received direct sun
light for part of the day. Nests were occasionally re-used
in successive years but in most cases they peeled off the wall
soon after the nesting season. Before re-use additional twigs
appeared to be added to the nest, as has been recorded for C.
pelgica (Amadon, 1936; Fischer, 1958). In but a few cases did
C. brachyura build up the semicircular arch of saliva on the
wall above the nest so diagnostic of C. pelgica nests (Fischer,
1958; Fig. 8). The absence of this additional support may
account for the more rapid destruction of C. brachyura nests.
Egg laying starts about 10 days after the beginning of con
struction and before the nest is completely finished. The
nests are unlined, but in two cases a feather was found glued
in among the sticks, and a large white feather was once found
in the bottom of a nest containing recently hatched young.
A variety of other organisms were also found in the
manhole nest sites. Those holes that were partially filled
with water usually contained the tree frog Hyla rubra. An
unidentified snake and a lizard, Ameiva ameiva, were each seen
on one occasion at the bottom of dry holes, presumably having
gotten there through the connecting drainage pipe. Wet and
dry holes alike often contained one or more nests of the "Jack
Spaniard" or paper wasp (Polistes canadensis), under the over
hanging edge of the top and the globular mud nest of the potter
wasp (Eumenes canaliculatus), on the walls. Spiders of several
types frequented the manholes, and on one occasion Snow (1962)
observed a large spider (Mygale sp.) pounce on and kill a

18
nestling which fell out of the nest.
Cypseloides rutilus
The nests of four of the ten species presently included
in the genus Cypseloides are still unknown. There is, however,
a good deal of similarity in both site and nest material among
those that have been described. Lack, in his review of the
nesting habits of swifts (1956a), states that "all the species
of Cypseloides for which the nest is reliably known agree in
building on steep cliffs, usually in association with water,
making a cone-shaped nest of mud and moss lined with fern-
tips or twigs." For Cypseloides niger (Gmelin), Knorr (1962)
has delimited five "ecological requirements" for nest sites:
"the presence of water, high relief inaccessibility
for terrestrial marauders, darkness, and lack of flyway obstruc
tions in the vicinity of the nest." This type of nesting
situation is so characteristic that numerous nests of C. niger
have been successfully found by searching for these "ecological
requirements" rather than birds showing indications of possible
breeding (Michael, 1927; Knorr, 1961, 1962). The same pro
cedure was used in this study to find additional C. rutilus
nest sites in Trinidad and, I am sure, could be applied with
equal success to locating the yet undescribed nests of C.
biscutatus (Sclater), C. cherriei Ridgway, C. cryptus Zimmer,
and C. lemosi Eisenmann and Lehmann. Only two nests attributed
to Cypseloides are not in agreement with this general pattern
or the descriptions of other nests of the same species. They
represent one nest each of C. fumigatus (Streubel) (Holt, 1927-

19
1928) and C. zonaris (Shaw) (Todd and Carriker, 1922). In
both cases the nests were described as being made of twigs
glued together with saliva. The nest of the former also con
tained five young and was located inside a house gable, an
%
improbable site and brood size for a species of Cypseloides.
Ihese nests are quite obviously more correctly referred to some
species of Chaetura.
In the first description of the nest of C. rutilus,
Orton (1871) states it to be "chiefly of moss, very compact,
and shallow, and located in dark culverts about two feet above
the water." Belcher and Smooker (1936) characterize nests
in Trinidad as "half cups stuck to a perpendicular wall of
rock over a swiftly running stream." Snow (1962)
describes the nest as "a substantial bracket, semicircular
in horizontal section with a wide depression for the eggs .
[and]. made of various plant fibers, usually including
some moss."
My observations indicate some variation in the shape
of C. rutilus nests. Some nests, built on smooth vertical
surfaces, in fact resembled truncated cones similar to those
of C. fumigatus and C. zonaris (Reboratti, 1918). Others,
located on small rock ledges, were little more than pads of
nesting material, somewhat thicker along the outer rim, with
a wide but shallow cup for the eggs (Fig. 4). This type of
nest closely resembles the "disk-shaped" ones reported for C.
zonaris and _C. niger when similarly located on damp rocky
ledges (Rowley and Orr, 1965; Michael, 1927). The shape of

20
Fig. 4. Nests of Cypseloides rutilus; a) "Cone-shaped,"
b) "disk-shaped."

21
the nest, then, seems to be entirely dependent on whether it
is affixed to a smooth rocky surface or perched on a narrow
ledge. Larger species such as C. zonaris, require greater
support for their nests and consequently would be expected to
build on ledges when available. The smaller and lighter weight
species such as C. rutilus and C. fumigatus, could also build
cone-shaped nests fixed to vertical surfaces. Presumably owing
to its extreme weight (170-180 g), the largest New World swift,
Cypseloides semicollaris (Saussure), builds no nest at all and
lays its eggs on sandy ledges in caves (Rowley and Orr, 1962).
Regardless of the shape, C. rutilus nests appeared to
be primarily of soft plant material with some mud intermixed.
This mud presumably helped hold the nest material together and
attach it to the rock as no salivary glue appeared to be used.
The universal use of saliva in swift nest construction has
already been questioned (Marshall and Folley, 1956; Johnston,
1961), and its use should not be assumed for C. rutilus until
further information is available. The plant materials used in
Trinidadian C^_ rutilus nests included a liverwort of the genus
Plagiochilax, the lycopsids Selaginella cladorrhizans and cf.
arthritica, and the filmy fern Trichomanes membranaceum. All of
these plants grow in damp shady places, particularly on rocky
outcrops along streams (Fig. 5) and thus in proximity to the
nest sites of these swifts. There is no information available
on the collection of the nest material or nest construction by
any species of Cypseloides. Nests are used during several
successive years, and a new lining of fresh green material is

22
Fig. 5. Nesting material of Cypseloides rutilus growing on
stream-side rock ledge.

23
added annually, with several distinct layers representing the
annual additions. Sea cave nests of C. rutilus appeared to be
constructed of slightly different materials and may well have
contained seaweed as reported for a similarly located nest of
C. niger (Legg, 1956).
C. rutilus nests have been found on rocky outcrops
overhanging pools in mountain streams (Fig. 6), on the rocky
walls of a river gorge, in sea caves, and also in man-made
culverts (Fig. 4a) and in one case on the underside of a bridge
(Belcher and Smooker, 1936; Snow, 1962). In general the sites
are similar to those for other species of Cypseloides in being
in deep shadow, inaccessible to terrestrial animals, and closely
associated with water. They do not strictly agree with the
ecological "requirements" outlined for C. niger in that they
are rarely associated with high relief. All nests of this
species have been found in forested areas at localities of
relatively low elevations from sea. level to 1100 feet. Most
nests were in deep shadow and none received direct sunlight.
Streamside nests were only 2-4 feet above the water, but nests
in a gorge were as much as 25 feet above the river, although
still in a damp situation owing to seepage water on the walls.
The sea-cave nests were about 6-8 feet above either permanent
water or tidal wash.
In contrast with the larger species C. zonaris and C.
niger, which nest near, and sometimes behind, waterfalls, only
one C. rutilus nest was near falling water. This nest was on
a smooth wall about 8 feet above a pool of water, into which

24
Fig. 6
SLreara nesting habitat of Cypseloides rutilus

25
poured a small waterfall, and just outside the spray zone of
the fall. Of the 15 nest sites observed during this study 2
were along mountain streams, 6 were in a river gorge, 4 in
sea caves, and 3 were in main-made culverts under a road or under
a bridge. Nine of these sites were found by Snow (1962).
The largest concentration of nests was in the rocky
walled "gucharo gorge" cut into limestone by the Arima River
near the head of Arima Valley. This gorge is located on the
Spring Hill Estate and has been a nesting place for these swifts
for at least 40 years, a nest being reported from there in 1926
(Belcher and Smooker, 1936). Individual nests were situated
along the gorge at varying intervals the least being about 35
feet. Elsewhere, the least distance I have recorded between
two active C. rutilus nests was about 7 feet. In this case
the two nests were on the walls of a cave-like rock archway
8 feet above a channel of water which cuts through Saut DEau
Island, an offshore islet on the north coast of Trinidad. It
is noteworthy that these swifts had to cross about a quarter
mile of ocean to reach the nearest feeding area. The swifts
inhabiting sea caves on Huevos Island probably also crossed
stretches of water in getting to mainland feeding area.
The most prominent organisms sharing these nest sites
were a variety of bats (mostly of the family Phyllostomidae)
which used the shady areas as daytime roosts. Several species
of small frogs and a cave cricket could be found in the vicinity
of the nest sites. On one occasion a small snake, Leptodeira


26
annulata, was caught on a ledge only a few feet from an active
swift nest. As its name implies, the "gucharo gorge" also
contained a small colony of the gucharo or oilbird, Steatornis
caripensis, as did two of the sea caves in which C. rutilus was
thought to nest (Snow, 1962).
Environmental temperatures at typical C. rutilus nest
sites ranged from 18.8-26.2 C, but h'ad a characteristic daily
range of 21.5-25.0 C. Sea cave nest sites tended to be a bit
warmer, with maximum temperatures reaching 27.2 C. The range
in temperature recorded over 13 months at one nest site in the
river gorge was 18.8-23.8 C. Relative humidity at the nest
sites was always in excess of 95 per cent.

BREEDING SEASONS
Most land birds in Trinidad have a well defined breeding
season. In contrast to the annual period of molt which shows
little yearly variation, the breeding season varies considerably
from species to species and from year to year (Snow and Snow,
1964). The breeding seasons for the two swifts C. brachyura
and C. rutilus extend from April until late August or early
September but vary within this period considerably from year
to year. The season coincides with the height of the annual
rainy period when insects are presumably most abundant, and
it probably represents an adaptive synchronization that assures
adequate food when young are to be fed. A similar adaptive
relationship seems to exist in Trinidad with the swallows,
which also depend upon flying insects for their food (Snow and
Snow, 1964).
Although the ultimate factor regulating the breeding
season seems to be an abundant food supply at the time of
nestling growth, the proximate environmental factors are more
obscure. The role of photoperiod as a proximate factor con
trolling breeding in tropical and equatorial birds is still
subject to debate. Experimental work has shown that the gonads
of several low-latitude birds respond to increasing photoperiods,
as has been amply shown for temperate latitude birds (Marshall
27

28
and Disney, 1956; Miller, 1959). However, the small annual
change in photoperiod at the lower latitudes makes it reasonable
to assume that these swifts and possibly other tropical birds
respond to a combination of photoperiod and some more variable
environmental stimulus similar to the situation in the erratically
breeding red crossbill, Loxia curivostra, of the temperate zone.
This crossbill shows only a partial response to increasing or
constant long photoperiods. The completion of gonadal develop
ment and the triggering of breeding is dependent upon some
proximate environmental factor as an increased availability of
suitable food (Tordoff and Dawson, 1965).
The most obvious environmental factor potentially
regulating the breeding of these Trinidadian swifts is the
onset of the annual rainy season. Even so, the response of
each of these two species is somewhat different. C. brachyura
usually begins nesting before C. rutilus and very soon after
the first heavy rains of the season. The first sign of breed
ing activity is the appearance of new nests or in some cases
the addition of new material to old nests. These activities
coincide with the start of the summer rainy season, and in
those years when brief heavy rains precede the period of intense
summer rainfall, C. brachyura often begins nesting at an earlier
date. For example, in 1959, there were heavy rains early in
April followed by a dry spell until the beginning of the true
summer rains in the middle of May. Ihis false start triggered
breeding by C. brachyura in April followed by a lull during the
dry spell and renewal of nesting activity in late May (Snow,

29
1962). In 1964 when there was an extremely wet winter and
spring, particularly in the more easterly parts of Trinidad,
the breeding activities of C. brachyura began very early,
although the main rainy season did not appear to start until
late May. A summary of the number of C. brachyura nests begun
in the years 1957 to 1964 in half-month intervals is presented
in Table 2. Several other Trinidadian birds appeared to be
directly influenced by the return of rainy weather. In several
cases the first strong rains of the season triggered repro
ductive activity. Almost immediately nest building and the
gathering of nest material was conspicuous and a peak in the
number of eggs laid soon followed (Snow and Snow, 1964).
Temporary dry spells also sharply reduced breeding in several
species.
C. rutilus started its breeding activities later than
C. brachyura and in most years showed a greater population
synchrony (Table 3). The first sign of their renewed nesting
was always the appearance of a fresh lining of greenery in the
old nests in preparation for their re-use. Prior to the start
of the rains this material is in short supply since much of it
dies away during the dry season and regains its previous lush
ness only when the rains return. It appears that C. rutilus
depends upon the reappearance of suitable nest material to
begin its breeding cycle. Such plant material is in turn de
pendent upon the return of the full summer rains and in some
cases the rising of water levels in the streams.

30
Table 2. Distribution of Chaetura brachyura nests in half-
month intervals.
Period
1957*
1958*
1959*
1960*
1961*
1962
1963
1964
All
Years
1 -15
April
1
1
2
16-30
April
1
1
3
2
7
1 -15
May
5
4
1
3
1
2
4
4
24
16-31
May
4
3
2
3
2
1
2
4
21
1 -15
June
1
4
3
4
2
14
16-30
June
1
1
5
1
2
4
1
15
1 -15
July
3
2
1
3
3
1
13
16-31
July
1
4
2
1
1
1
**
1
11
1 -15
Aug.
3
1
2
3
1
**
1
11
16-31
Aug.
3
1
**
4
1 -15
Sept.
1
1
1
**
3
Total
19
16
16
14
21
13
12
14
125
*Data from Snow (1962)
**No observations

31
Table 3. Distribution of Cypseloides rutilus nests in half-
month intervals
Period
1957*
1958*
1958*
1960*
1
1961*
1962
1963
1964
All
Years
1 -15 April
16-30 April
1
1
1-15 May
1
1
1
3
16-31 May
1
1
2
1
5
6
16
1 -15 June
1
1
2
3
5
1
13
16-30 June
1
2
1
2
6
1 -15 July
2
1
3
16-31 July
2
1
2
1
2
**
8
1 -15 Aug.
1
1
1
2
1
1
**
4
11
16-31 Aug.
1
3
2
**
2
8
Total
2
9
7
8
9
11
10
13
69
Data from Snow (1962)
No observations

32
This sequence of events was particularly noticeable
in 1964. In that year the easterly parts of Trinidad experi
enced a very wet winter and spring. As mentioned (p 29), this
unseasonable wet weather stimulated very early breeding by C.
brachyura in that area. At the same time Arima Valley had a
fairly normal dry season which did not end until 22-23 May.
These two days were marked by nearly'continuous heavy rains.
Prior to this time there had been no indication of breeding
that year at any known C. rutilus nest site in the valley.
The stream water levels were low and suitable nest material
was unavailable. Several days after these first heavy rains
the mossy stream-side plant life had recovered a great measure
of its former lushness. On 29 May six C. rutilus nest sites
were checked and all six nests were relined with fresh greenery.
On 3 June three of these contained one or more eggs. By 6 June
four of the six nests had full clutches while a fifth contained
a partial clutch. The remaining nest, although relined, was not
used that year.

CLUTCH SIZE
Like other species of Chaetura, C. brachyura lays
large clutches. The 26 complete clutches observed from 1962
to 1964 ranged from 2-7 eggs, with a mean clutch size of 3.8
(Table 4). This is 'slightly less than for the other Chaetura
species that have been studied (Table 5). In the earlier
observations on this same population from 1957 to 1961, 41
clutches ranged in size from 1-6 and had a mean of 3.6 eggs
per clutch (Snow, 1962; Table 2). Unusual clutches of 8 and
9 have been recorded for C. pelgica and C. brachyura, re
spectively, but in each case they appeared to result from two
females laying in the same nest (Fischer, 1958; Snow, 1962).
The 7-egg clutches recorded for C. vauxi (Baldwin and Zaczkowski,
1963) and C. brachyura (this study) both seemed to be the product
of a single female. In both of these cases the eggs were laid
or hatched within a short time of each other.
An additional example of two females laying in a single
nest was noted for C. brachyura in 1963. In this case a clutch
of 4 eggs was laid in a newly constructed nest between 7-13 May
at the usual rate of 1 egg every other day. Incubation began
on 14 or 15 May, and the clutch still consisted of only 4 eggs
on 17 May. On 21 May, however, a fifth egg was noticed and
when the nest was checked on 23 May a sixth had been added.
33

34
Table 4. Distribution of clutch sizes of Chaetura brachyura
by half-month intervals for years 1962 to 1964.
Clutch Size
Totals
Period 1
2
3
4
5
6
7
16-30 April
1
1
2
1 -15 May
1
2
2
5
16-31 May
1
1
3
1
6
1 -15 June
1
1
16-30 June
2
1
1
4
1 -15 July
2
1
1
4
16-31 July
1
1
2
1 -15 Aug.
1
1
16-31 Aug.
1
1
All months 0
3
8
8
5
1
1
26

35
Table 5. Clutch size of swift species in the genus Chaetura.
Species
Number
of
clutches
Range
Average
clutch
size
Reference
C. pelgica
25
2-5
4.2
Fischer, 1958
T
27
3-7
4.0
Dexter (in Fischer, 1958)
t!
19
4-6
5.3
Sherman, 1952
C. brachyura
41
H
O'
3.6
Snow, 1962
It
26
2-7
3.8
this study
C. andrei
3
4-5
4.6
Sick, 1959
C. vauxi
?
3-7
?
Baldwin & Zaczkowski,
1963; Bent, 1940.
J

36
Four two-day-old young and two eggs were in the nest on 2 June,
after an incubation period of approximately 17 days. The re
maining two eggs hatched on 6 and 7 June and both of the newly
hatched young birds were found later the same day dead or nearly
dead on the floor of the nest cavity. Presumably they were
inadvertently shoved out of the nest by the movements of the
older and stronger nestlings. An evening check of this nest
showed three adults roosting together near the nest; one of them
was known to be a yearling bird raised in that nest cavity the
preceding year.
Two females trying to lay in the same nest may have
caused disruption of egg laying and ejection of eggs in two
other cases. Adult birds were frequently observed roosting
in nest cavities with a nesting pair, although not in close
approximation. At three additional nests extraparental coopera
tion was observed in the feeding of the young.
In C. pelgica extraparental cooperation occurs regu
larly and may involve birds of all ages and both sexes includ
ing young of the previous year. These helpers share in the
incubation and brooding duties as well as the feeding of the
young (Dexter, 1952). Further observations with individually
marked birds might well show it to be of regular occurrence
in C. brachyura. The cause of such extraparental cooperation
in Chaetura is not yet clear. It may be due to a shortage of
nest sites as suggested by Snow (1962), or to the inability of
some birds to find mates as suggested by Dexter (1952). Skutch
(1961) feels that such activities in passerine birds may

37
represent an adaptive curtailment of the reproductive rate
favoring the greater survival of a lesser number of young.
Eggs were usually laid at the rate of one every other
day. On a few occasions disturbances of the nest or inclement
weather appeared to prolong the laying period. Five eggs in
a single clutch weighed 1, 1, 1, 1-1/4 and 1-1/2 grams.
Clutch size in C. rutilus is very small, as is true
of all species of Cypseloides. Of 25 clutches observed from
1962 to 1964, 23 were of 2 eggs and 2 of 1 egg. Of 32 clutches
observed by Snow only one case of a clutch of a single egg was
noticed and he attributed this to a bird breeding for the first
time.
The interval between the laying of the two eggs was
more irregular than for C. brachyura. The second egg of the
clutch was usually laid two days after the first, but intervals
of as long as five days occurred during which the first egg was
left uncovered in the nest. The eggs from two clutches weighed
2-1/4, 2-3/4, 2-3/4 grams. Extraparental cooperation was not
observed in this species.

INCUBATION
The incubation period was calculated from the laying of
the last egg to the hatching of the last young. For C. brachyura
the 17-18 day period determined by Snow (1962) was confirmed,
except in one case, when the period was only 16 days. A period
of 48-72 hours usually elapsed between the hatching out of the
first and last young.
The incubation period for all clutches of C. rutilus
agreed with the 22-23 day period determined by Snow (1962).
The siblings in the broods of two usually hatched within 24
hours of each other.
Although substantial losses often occurred during the
incubation period, there was a high percentage of hatching
among those eggs of both species which reached the expected
date of hatching (Table 6). The figure recorded in this study
for C. rutilus (84.3 per cent) is lower than that of Snow (93.1
per cent) because of the desertion of a clutch and it may have
resulted from the greater frequency of disturbing visits. Thus
the higher value may be more characteristic of undisturbed
nests. The hatching rate, based on the total number of eggs,
is quite low for both species as compared with similar values
for other swifts (Table 6). Those species showing a high
hatching success are also those with the more inaccessible
38

Table 6. Average hatching and fledging success of swift species.
Species
Eggs hatched of
No. completely
incubated (%)
Eggs hatched
of No. laid
(%)
Young fledging
of No. eggs
hatching (%)
Young fledging
of No. eggs
laid (%)
Apus apus^
(England)
74.011
74.5
59.0
Apus apus2
(Switzerland)

76.0
85.8
65.2
o
Apus melba
94.4
86.0
80.9
76.0
Apus caffer^
98.9
88.6
86.0
76.2
(Kenya)
Apus caffer-5
81.0
70.3
57.0
(South Africa)
Cypsiurus parvus^

54.2
31.5
17.1
Chaetura pelgica7

89.5
96.1
86.0
Chaetura brachyura8
95.0
51.7
53.5
26.7 K
Cypseloides rutilus^
93.1



Cypseloides rutilus8
84.3
65.8
68.4
36.1
Collocalia maxima^

29.2
65.4

Collocalia esculenta^

76.1
74.7

Collocalia salangana^

51.5
78.5

Lack and Lack, 1951. ^Weitnauer, 1947. ^Lack and Arn, 1947. ^Moreau, 1942a.
^Schmidt, 1965. ^Moreau, 1941. ^Fischer, 1958. 8This study. ^Snow, 1962. ^Medway, 1962a.
78.0 per cent when eggs ejected prior to start of incubation are omitted.
to
vo

40
nest sites. The higher hatching success of C. rutilus, compared
to C. brachyura, is probably similarly based on the fact that C.
rutilus nests overhang water on smooth surfaces or inaccessible
ledges, and are less often disturbed by predators than the nests
of C. brachyura in manholes or hollow trees. Several of the
"inaccessible" sites recorded for other species were in man-made
structures and may not, therefore, reflect mortality rates when
under natural conditions.

PARENTAL CARE
The period during which the young are under parental
care is divided into nestling and fledgling periods. The nest
ling period includes the time the young are in the nest. The
fledgling period is when the young are out of the nest but in
capable of flying and are still being fed by the adults. These
periods are quite different in the two species of swifts in this
study. In C. brachyura there is a well defined nestling and
fledgling period while in C. rutilus these two periods overlap..
Chaetura brachyura
Nestling period. The young of C. brachyura spend the
first three weeks of their lives in the nest. Some birds leave
the nest as early as day 20 but most remain in it until 22-23
days after hatching. Those in larger broods tend to leave the
nest sooner than those in smaller ones.
Fledgling period. C. brachyura has a fledgling period
lasting about two weeks during which the young are out of the
nest clinging to the walls of the nest cavity. Most of the
fledglings remain in the nest cavity until they are 30-36 days
old, and occasional individuals stay until they are about 40
days old, even though they may be capable of leaving as early
as 26 days after hatching. In one extreme case two young birds
were still roosting in the nest cavity and being fed by the adults
when 49 and 50 days old, respectively.
41

42
The ultimate factor governing departure of the fledglings
is probably the cessation of feeding by the adults. Young birds
quite capable of flying were observed to spend much or all of
the day roosting in the nest cavity, so long as the adults con
tinued to feed them. Several birds, which escaped while being
handled, successfully flew away and yet were found again roosting
on subsequent daytime visits. Snow (1962) also observed young
birds to "return to their nest hole by day after their first
flight." It is quite possible that young birds more than 30
days old, still found roosting by day, were making occasional
short flights before entirely abandoning the nest cavity. Two
35-day-old swifts, caught roosting in their nest cavity, were
fully capable of sustained flight at this age and successfully
returned when released at a point nine miles away. The earlier
observations by Snow (1962) indicated that "the young can fly
if disturbed as early as 28 days after hatching;if undisturbed,
they do not usually leave until they are 30-40 days old."
Cypseloides rutilus
In C. rutilus, as in all swifts except species of
Chaetura, there is no separation of the nestling and fledgling
periods as the young remain in the nest until the time they can
fly and feed themselves. This combined nestling-fledgling period
in C. rutilus is somewhat longer than in C. brachyura, being
closer to 40 days. All available figures exceed 35 days and most
fall between 37-43 days, averaging 39-30 days. These figures are
in agreement with those determined by Snow (1962). Young C.

43
rutilus have been seen on occasion to exercise their wings while
"hanging to the outer rim of the nest" (Snow, 1962). Any attempts
to clamber about on the rocky walls adjoining the nest would
probably result in death, as these surfaces are usually smooth
and often wet and slippery.
The combined nestling-fledgling periods for most swifts
are between 35-45 days, with larger species requiring slightly
longer than smaller ones. Usually short periods of 29-32 days
were noted for Cypsiurus parvus (Lichtenstein) and 30 days for
Chaetura pelgica (Moreau, 1941; Fischer, 1958). Slight geo
graphic variation in the nestling-fledgling period has been noted
in Apus caffer (Lichtenstein), which averages 42 days in Kenya
and 46 days in South Africa (Moreau, 1942a; Schmidt, 1965).
Weather conditions can also affect the length of this period,
bad weather extending it as much as two days (Lack, 1956b).

BROODING
Until they are about two weeks old, nestlings of both
swift species are brooded at night by one or both parents. By
this time the young are too large to be covered by the adults.
During the first days of their life nestlings of C. brachyura
are regularly brooded for long daytime periods, and for shorter
periods, of 20 minutes duration or less, as late as 8 days after
hatching. As early as the second day after hatching, however,
both adults are sometimes absent, presumably foraging for the
young. Nestlings of C. rutilus usually are continuously brooded
during the daytime for the first 10-11 days, and occasionally as
late as 13 days after hatching.
Most species of swifts brood during the daytime for
most of the first week of nestling life, although both adults
may be absent for short periods, particularly around dusk.
Thereafter, daytime brooding is sporadic and highly variable in
duration. In England, daytime brooding was recorded in Apus
apus for 98 per cent of the time during the first week of nest
ling life, up to 52 per cent during the second week, and 7 per
cent or less thereafter.
44

FLEDGING SUCCESS
The mortality during the nestling and fledgling periods
for C. brachyura was approximately equal to that during incuba
tion (Table 6). Only 53.5 per cent of the 58 hatchlings suc
cessfully fledged, and only 26.7 per cent of the 112 eggs laid
resulted in fledged young. For C. rutilus the mortality rates
of eggs and nestlings were also about equal, with 68.4 per cent
of the 19 hatchlings successfully fledging, or only 36.1 per
cent of the total of 36 eggs laid.
As indicated by Snow (1962), the figures for C. brachyura
may not be typical of nests other than in man-made structures,
and there may well have been some additional mortality resulting
from the frequent visits and repeated handling which were part
of this study. There is, however, no information available for
any species of Chaetura in a natural nest site. The only
information on other Cypseloides swifts is for CL niger, which
had a similarly high rate of nest failures, particularly in the
nestling stage (Hunter and Baldwin, 1962).
The causes of egg and nestling losses are not clear.
At least one nestling of Cypseloides niger was seen to fall from
the nest (Knorr, 1961:168), and it is possible that many of the
losses of C. rutilus are similarly due to young birds accidentally
failin9 out of the nest. This is less likely in C. brachyura in
45

46
light of the strength of their feet and their ability to hold
tenaciously to the nest, even at very early ages.
No predation of eggs or nestlings has been observed for
either species. Two nestlings of C. brachyura and one of C.
rutilus were found that had been badly chewed by some animal.
As these nests were inaccessible to terrestrial predators it is
possible that this was the result of an attack by a bat of one
of the several species which commonly roosted in close proximity
to the swift nests. Other losses of both nestlings and eggs
might also be attributed to bat predation. Skutch (1964)
similarly suspected bats to be responsible for the disappearance
of eggs and nestlings from the inaccessible nests and the wounding
of a nestling of a hermit hummingbird. Some egg losses were also
probably due to accidental ejection from the nest by the adults,
as has been observed for other species (Lack and Lack, 1951;
Moreau, 1942a).

GROWTH
Body weight
A total of 321 nestling weights was obtained in the
field, from a total of 57 chicks from 15 nests of C. brachyura
(Fig. 7). From 1-15 weights were obtained from a single nest
ling. A total of 165 weights of C. rutilus nestlings was ob
tained from 25 individuals weighed between 1-16 times each
(Fig. 8).
At hatching the average weight of C. brachyura nest
lings was 1.6 grams and 18 days later it reached a maximum of
21.2 grams, a 13.3-fold increase. At fledging they had reached
approximately 87 per cent of their adult weight.
The average weight of C. rutilus at hatching, was 2.1
grams, and it reached a maximum average weight of 26.2 grams on
day 29, a 12.4-fold increase. At fledging C. rutilus weighed
approximately 119 per cent of the adult weight.
The instantaneous percentage growth rate, calculated
for each day (Brody, 1945: 508), tended to decrease in both
species after an initial rise (Tables 7-8). C. brachyura had
its peak growth rate on the fourth day after hatching: the
similar peak for C. rutilus did not occur until the seventh
day. The average weight gain per day and the average per cent
growth rate per day were calculated for 7 five-day periods
during the nestling life of these two species (Table 9). These
47

WT. IN GRAMS
Fig. 7. Growth curve of Chaetura brachyura. Semi-log plot, vertical lines
represent range of daily weights, curve connects daily means.
00

WT. IN GRAMS
+
I Ji'iiiiii 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
AGE IN DAYS
Fig. 8. Growth curve of Cypseloides rutilus. Semi-log plot, vertical lines
represent range of daily weights, curve connects daily means.
I|r
36
vo

50
Table 7. Daily weight (grams) and relative growth rate (per
cent) of Chaetura brachyura.
Days from
hatching
No.
Mean
weight
Range
Mean
weight
change
Per cent rela
tive growth
per day
0
20
1.6
1
0 -2.1/2
__
,
1
18
2.1
1
1/4-2.3/5
0.5
27.1
2
13
2.8
2
1/4-3 1/2
0.7
28.7
3
10
3.7
2
1/4-4 1/2
0.9
27.8
4
10
5.1
3
1/2-6 1/4
1.4
34.0
5
10
6.3
5
3/4-7 1/4
1.2
19.1
6
8
7.4
6
-9
1.1
16.0
7
9
8.7
4
-11
1.3
16.1
8
16
11.1
8
1/4-15
2.4
24.3
9
9
11.2
5
1/2-15
0.1
0.8
10
15
13.5
11
1/2-16 3/4
2.3
18.6
11
14
16.1
13
-19 1/2
2.6
17.6
12
14
16.2
13
1/2-19.
0.1
0.6
13
7
18.3
15
3/4-20
2.1
12.1
14
9
19.0
17
1/2-21 3/4
0.7
3.7
15
11
18.1
13
-22 1/4
-0.9
- 8.6
16
8
19.1
17
1/2-21 1/2
1.0
13.9
17
7
19.6
18
-22
0.5
2.5
18
6
22.2
17
3/4-22 1/2
2.6
12.4
19
7
20.2
17
1/2-23 3/4
-2.0
- 9.4
20
5
20.9
19
1/2-23
0.7
3.4
21
7
20.2
17
3/4-22 1/2
-0.7
- 3.4
22
6
19.0
17
1/4-22 1/2
-1.2
- 9.5
23
5
18.9
16
-21
-0.1
- 0.5
24
8
18.8
13
3/4-21 1/4
-0.1
- 0.5
25
11
19.7
16
-21
0.9
4.6
26
7
19.0
15
1/2-21 1/4
-0.7
- 3.6
27
7
19.4
17
1/2-23
0.4
2.0
28
6
18.0
17
-20
-1.4
- 7.4
29
6
18.7
17
1/4-21 3/4
0.7
3.9
30
6
18.4
16
1/4-20 1/4
-0.3
- 1.6
31
7
16.5
14
1/4-18 1/2
-1.9
-10.8
32
3
17.0
16
-18 1/2
0.5
2.9
33
5
16.6
15
-17 3/4
-0.4
- 2.3
34
4
15.7
14
1/4-17
-0.9
- 5.5
35
4
15.4
13
-17
-0.3
- 1.9
36
1
16.0
--
0.6
3.8
37
2
14.3
13
1/2-15
-1.7
-11.2
*

51
Table 8. Daily weight (grams) and relative growth rate (per
cent) of Cypseloides rutilus.
Days from
hatching
No.
Mean
weight
Range
Mean
weight
change
Per cent rela'
tive growth
per day
0
7
2.1
2
-2 :
1/2
1
10
2.5
2
-3
0.4
17.4
2
7
3.5
2
3/4-4 1/2
1.0
33.6
3
10
3.9
3
1/4 -5
0.4
10.8
4
8
5.0
4
1/4 -6 :
1/4
1.1
24.8
5
13
6.3
5
1/2 -7 .
3/4
1.3
23.1
6
7
7.3
6
1/2 -8 :
3/4
1.0
14.7
7
7
10.6
8
-14
1/2
3.3
38.2
8
4
9.8
8
1/2 -12
1/4
-0.8
- 8.7
9
10
11.6
8
-13
1.8
16.8
10
3
12.8
9
3/4 -14
1/4
1.2
9.8
11
7
14.1
11
1/2-16
1.3
9.6
12
6
15.8
14
-18
1/2
1.7
11.3
13
6
16.6
14
1/2-17
3/4
0.8
4.9
14
4
18.2
17
-19
3/4
1.6
9.2
15
1
20.5
--
2.3
11.9
16
6
20.7
18
1/2-21
1/2
0.2
0.9
17
1
19.3

-1.4
- 7.0
18
6
21.0
20
-22
1.7
8.4
19
4
21.2
18
-26
3/4
0.2
9.3
20
4
23.9
21
1/2-24
3/4
2.7
11.9
21
6
22.5
18
1/2-26
-1.4
6.0
22
2
20.8
20
1/4-21
1/4
-1.7
- 7.8
23
3
25.5
25
-27
1/2
4.7
20.3
24
1
23.0

-2.5
-10.3
25
3
25.2
24
3/4-25
3/4
2.2
9.1
D
27
3
24.2
24
-25
-1.0
- 4.0
28
1
24.0

-0.2
- 0.8
29
3
26.2
23
1/4-28
3/4
2.2
8.7
30
4
23.6
22
1/2-26
1/4
-2.6
-10.4
Jl
32
1
20.3

-3.3
-15.0
34
3
24.4
23
326
1/2
4.1
18.3
35
1
24.0

-0.4
- 1.6
36
2
23.9
22
1/2-25
1/4
-0.1
- 0.4
37
1
24.3

0.4
1.6

52
Table 9. Average daily growth rate (grams) and relative growth
rate (per cent) for five-day intervals for Cypseloides rutilus
and Chaetura brachyura.
Age
C. brachyura
Mean daily Mean daily
weight relative
change growth rate
C. rutilus
Mean daily Mean daily
weight relative
change growth rate
0-4
0.9
29.4
0.7
21.7
5-9
1.2
15.3
1.3
16.8
10-14
1.6
10.5
1.3
9.0
15-19
0.2
2.5
0.6
4.7
20-24
-0.3
-2.1
0.4
1.6
25-29
-0.02
-0.1
0.8
3.3
30-34
-0.6
-3.5
-0.4
-2.3

53
figures show that C. brachyura has an initially higher average
daily weight gain and average per cent growth rate that sub
sequently decline rapidly. After approximately three weeks of
nestling life the young begin to los weight, particularly when
they first leave the nest and again later when they begin to
fly. C. rutilus, on the other hand, has an initially lower
average daily weight gain and average percent growth rate which
also declines although at a slower rate so that the nestlings do
not begin to lose weight until late in the nestling period
approximately 4 1/2 weeks after hatching.
The general pattern of growth shown by these two swifts
is similar to those reported for most altricial birds, particu
larly those with longer periods of development (Dawson and Evans,
1957, 1960; Maher, 1964; Kahl, 1958). identical in growth pattern to C. pelgica and C. vauxi, the
only previously studied species of Chaetura (Fischer, 1958;
Baldwin and Zaczkowski, 1963). C. rutilus is most similar in
growth pattern to European species in the genus Apus with
similarly long fledging periods (Lack and Lack, 1951; Weit-
nauer, 1947). No information is available for any other
Cypseloides species.
General development
Feathers. Like other species of swifts, C. brachyura
C. rutilus are hatched naked. Approximately 4 days after
hatching the developing contour feathers appear under the skin
as dark dots along the feather tracts. The remiges are first

54
to break through the skin, usually doing so around day 4-5.
The rectrices are somewhat slower, emerging on about day 6-7,
followed by the contour plumage when the birds are about 8 days
old. The feathers of the dorsal tract grow somewhat faster
than those of the cervical, capital, and ventral tracts and begin
to emerge from their sheaths about 15-16 days after the young
hatch. Emergence in the remaining tracts is somewhat later.
The flight feathers begin to break out of their sheaths 12-13
days after hatching. The growth of the wing is shown in Fig. 9
and the tail in Fig. 10. The tail completes its growth about
26-27 days after hatching, but the wing does not reach full
length until shortly after fledging.
C. rutilus acquires its feather covering in a sequence
generally similar to that of C. brachyura but it differs
slightly in timing. The remiges first break through the skin
on about day 5, and the rectrices about 9 days after hatching.
The contour plumage first appears as dark subcutaneous streaks and
emerges through the skin about 10-11 days after hatching. The
flight feathers begin to emerge from their sheaths about 13-14
days after hatching, about one day later than noted for C.
brachyura. The contour feathers, however, begin to break through
their sheaths much earlier in C. rutilus despite their having
emerged through the skin somewhat later than in C. brachyura.
These feathers begin to erupt 13 days after hatching as opposed
to day 15-16 for C. brachyura. The contour feathers of C.
rutilus on the cervical, capital, and ventral tracts are some
what slower in their development than those of the dorsal tract,

WING LENGTH IN MM
Fig. 9. Growth of the wing of Chaetura brachyura and Cypseloides rutilus.
Vertical lines represent ranges, curves connect daily means. Wing length
measured along chord from carpal joint to tip of longest primary.
Ui
in

TAIL LENGTH IN MM
Fig. 10. Growth of the tail of Chaetura brachyura and Cypseloides rutilus.
Vertical lines represent ranges, curves connect daily means.
Ul
o

57
as also noted for C. brachyura. The tail reaches its full
length about the time the young fledges (Fig. 9), but the wing
does not complete its growth until early in the post-fledging
period (Fig. 10).
The major difference in the plumage development of
Chaetura and Cypseloides species is the appearance in the latter
group of a dark gray, down-like covering early in nestling life,
prior to the appearance of the regular contour feathers. Al
though referred to as natal down by earlier observers it has
been shown to consist of a loose-webbed semiplume type of
feather and forms part of the first teleoptile plumage (Collins,
1963). These feathers appear as subcutaneous dots as early as
the first day of nestling life. They may break through the skin
as early as 5-6 days after hatching although usually somewhat
later. They routinely emerge earlier than the previous estimate
of 8-9 days after hatching (Collins, 1963). These semiplumes
are freed of their sheaths for more than half of their length
shortly after they erupt from the skin, and thus the nestling
soon takes on a downy appearance (Collins, 1963; Fig. 3). The
semiplumes seem to reach their full length of about 13-14 mm
by day 19 and are entirely freed of their sheaths by day 26.
They are covered by the emerging contour plumage at about 28
days after hatching. Semiplumes are longest on the back and
rump and shorter on the head and underparts. They are found on
the margins of the pterylae, particularly on the dorsal aspect
of the body. Although semiplumes are generally absent from
the wings, there are occasionally a few along the lateral
/

58
margin of the humeral tract and a short row of them in the
apterium between the lesser secondary coverts and the marginal
coverts (Collins, 1965). A similar down-like plumage has been
recorded for other Cypseloides species (Hunter and Baldwin,
1962; Orr, in litt.) and probably occurs in all members of the
genus. The semiplume covering and the early emergence of the
contour feathers from their sheaths are aids to thermoregulation
in nestlings living in a cooler microclimate.
Eyes. The two species have a noticeable difference in
the opening of the eyes. Those of C. brachyura are partially
open on day 16 and completely open on day 18. This is slightly
later than has been observed for other species of Chaetura
(Fischer, 1958; Baldwin and Zaczkowski, 1963). In C. rutilus
they open gradually with an interval of more than a week between
the first partial opening and complete opening of the eyes. In
this species the young may have partially opened eyes as early
as day 7, but usually this first occurs on day 8-9. Their
eyes are not fully open until about 16-17 days after hatching.
Bill and feet. The newly hatched swifts of both species
are pale flesh pink except for the bill and claws which have a
slight gray pigmentation at the tip, especially apparent in C.
brachyura. The lining of the mouth is also a flesh pink. In
both species a prominent egg tooth is present on the upper man
dible (similar structures were reported in other genera by
Parkes and Clark, 1964), and a hardened whitish cap occurs on
the lower mandible. The egg teeth gradually disappear during

59
the first weeks of nestling life. Both egg teeth are generally
unobservable by day 14, although a slight roughness on the culmen
sometimes can be detected on slightly older birds.
Grasping with the feet was noticed on the first day after
hatching in both species. The legs of C. brachyura seem to be
particularly well developed even very early in life and are
capable of supporting the nestling on a vertical surface within
48 hours after hatching. The feet of C. rutilus cannot support
a nestling in a similar fashion until about day 14. Michael
(1933) similarly noticed that Cypseloides niger had "the dainty
feet and slender legs of a songbird" and not the stronger limbs
characteristic of the white-throated swift, Aeronautes saxatilis
(Woodhouse). In their study of Chaetura vauxi, Baldwin and
Hunter (1963) also comment upon the particularly sharp claws
and strong toes as compared to Cypseloides niger. As was also
found in this study, Baldwin and Hunter (1963) note that the
young of Chaetura held on to the twigs of the nest so tenaciously
that a loss of claws was likely to result if care were not taken
in removing them from the nest. The strong feet of Chaetura
are an obvious adaptation enabling them to raise a larger brood
in their small nests. The ability to hold tightly to the nest
reduces the chances of one of a large brood being accidentally
jostled out of the nest, particularly during defecation. When
the nestlings are older and the nest becomes overcrowded (Fig.
11a) their strong feet enable them to climb out and support
themselves on the wall nearby until actual fledging (Fig. lib).

60
Fig. 11. Chaetura brachyura nestlings and fledglings,
a) in the nest shortly before leaving, b) on wall near nest.

61
Behavior. The vocalizations of these nestling swifts
are quite limited. C. rutilus nestlings only make a very soft
twittering when disturbed and give no calls during feeding. By
comparison C. brachyura nestlings utter a prolonged loud rasping
rattle when disturbed and particularly during feeding. This
call starts and stops abruptly, and if one bird starts, its
nest-mates are quick to join in. This "disturbance" call
(Fischer, 1958) is restricted to the time of feeding and its
associated activity and excitement once the eyes are open.
Prior to this the slightest disturbance, whether an external
influence or merely the sudden activity of one member of the
brood, may trigger this call, which can be heard at some distance.
Neither of these swifts foul the nest during the nestling
period. Fecal wastes are carefully voided over the rim of the
nest by the young swifts. As noted by others this often results
in large accumulations of trash under the nests. Much of the
material found below swift nests, however, consists of the
chitinous remains of their insect food and does not appear to
have passed through the digestive tract. Legg (1956) found
insect remains around a nest of Cypseloides niger, part of which
appeared to be in the form of a pellet. Thus it seems probable
that swifts, like many other insectivorous birds, regurgitate
pellets made up of the indigestible chitinous portions of their
insect prey and that much of the material accumulated under their
nests, or in some cases in the nest (Rowley and Orr, 1965), comes
from these pellets.

62
Development of Horneothermy
Young swifts of both species essentially lack any
thermoregulatory capacity at hatching. When they are not
brooded their body temperature quickly drops to near ambient
temperature (Figs. 12-13). Body temperatures as low as 25-
27 C were recorded for C. rutilus; the lowest body temperature
recorded for C. brachyura nestlings was 31.9 C. The thermo
regulatory capacity of both species improves as they grow older,
and at the end of the third week of nestling life there is little
decline in body temperature even during extended periods without
brooding.
Nestlings tested in a cold chamber (Fig. 1) at approxi
mately 5 C showed rapid decreases in body temperature, as much
as 9.8 degrees within 5 minutes. A total of 101 tests were made
on 31 nestlings of C. brachyura and 72 tests on 12 C. rutilus.
The rate at which body temperature dropped lessened sharply with
increasing age (Fig.. 14). This lessening in temperature decline
represented an increase in the thermoregulatory capacity of the
nestlings through both an increased capacity for thermogenesis
and decreased heat loss. The decrease in body heat loss could
be due to the appearance of an insulating feather coat or a
decrease in the surface to volume ratio of the nestling. C.
rutilus seems to have an efficient coat of insulation early in
nestling life in the form of a down-like semiplume covering.
In addition, its contour plumage grows in very rapidly. C.
rutilus and C. brachyura, however, perfect their thermoregulatory

BODY TEMPERATURE
40-
o
0 38-
3 6-
34-
32-
1 1 1 1 r
6 8 10 12 14
AGE IN DAYS
~l r-
16 18
I I
20 22
Fig. 12. Body temperatures of nestlings of Chaetura brachyura when
unbrooded.- Vertical lines represent daily range in body temperatures,
curve connects daily means. Typical daily range in ambient temperature
26.0-30.5 C.
O'
w

BOOY TEMPERATURE #C
0.2 4 6 8 10 12 14 16 18 20 22
AGE IN DAYS
Fig. 13. Bod;/ temperatures of nestlings of Cypseloides rutilus
when unbrooded. Vertical lines represent daily range in body
temperatures, curve connects daily means. Typical daily range
in ambient temperature 21.0-25.0 C.
o
-P-

AGE IN DAYS
Fig. 14. Decrease in body temperature of nestling swifts under cold stress.
Vertical line represents the range, and rectangles two standard errors on
either side of the mean.

66
capacities at about the same rate and there is little difference
in their body weight, and hence surface to volume ratio, during
their first two weeks of life. Thus it would seem that C.
brachyura must depend upon increased heat production to counter
act the effects of cold environmental temperatures. As the en
vironmental temperatures of their nest sites are usually quite
warm, they are only rarely exposed to such cold conditions and
the need for increased thermogenesis.
Torpor
The insect food of swifts may be markedly affected by
varying weather conditions. In the temperate regions, where
acute food shortages lasting several days are of common occur
rence, both adult and nestling swifts routinely drop their body
temperatures at night and enter a state of torpor (Koskimies,
1950I Bartholomew, Howell, and Cade, 1957). The young of Apus
apus can fast as long as 9 days by utilizing their stored fat
deposits and decreasing their body temperature and metabolism
at night (Koskimies, 1950). Similar reactions have been observed
for several species of tropical swifts when deprived of food
for several days in captivity (Howell, 1961; pers. obser.).
Under natural conditions no healthy adult or nestling of either
C. brachyura or C. rutilus exhibited a body temperature below
the maximum that it was capable of maintaining, and none appeared
to be in less than a fully active, awake condition. On several
occasions nestlings which appeared to be injured or in an ex
tremely weakened condition had abnormally low body temperatures.

67
In most cases these young were dead or missing from the nest
at the next visit. The capacity for dropping into torpor may
exist in all swifts, but it does not appear to be utilized in
the normal course of events by either C. brachyura or C. rutilus.

ADULT WEIGHT
The average adult weight of C. brachyura, based on a
sample of 240 individual weights, was 18.3 g with a range of
15 1/2-22 g. Snow (1962) reported an average weight of 19.8
g, but this value was influenced by the inclusion of a very
fat, non-breeding female weighing 30 grams, a weight 8 g
heavier than any other recorded for C. brachyura. This value
is however, within the expected weight range of the extremely
similar species Chaetura chapmani, to which perhaps it should
be attributed. The average weight of 24 juveniles of C.
brachyura, captured in roosting flocks of adults during Septem
ber and October 1964, was not appreciably different from that
of the adults although a few juvenile individuals ranged as
low as 14-15 grams, which is below the minimal weight recorded
for any adult.
The average adult weight of C. rutilus was 20.2 g and
ranged from 17 3/4-24 1/4 g in a sample of 45 individual weights.
There was a slight sexual dimorphism, males being heavier than
females. The weights of 24 males averaged 20.6 g and ranged
from 19 1/4-22 1/4 g while 19 females averaged 19.6 g with a
range of 17 3/4-24 1/4 grams. This difference is significant
(P<.02).
Monthly mean weights for both sexes of C. brachyura
68

69
varied between a low of 17.1 g (Oct. 1964) and a high of 18.7 g
(Aug. 1964). Daily means somewhat higher (18.9, 19.0 g) were
also recorded during August 1964. Eighteen individuals weighed
on two or three separate occasions, varied from as little as
1/4 g to as much as 2 1/2 g between successive weighings.
Monthly mean weights of C. rutilus varied from a low of 19.6
g to a high of 20.7 g, while daily sample averages varied from
19.0 to 21.1 g, both in October 1964. Eight individuals weighed
on two to four separate occasions varied as little as 1/4 g and
as much as 2 1/2 g between weighings.
Weight variations of these magnitudes are explainable
in terms of temporal variations in food availability. Similar
weight changes were recorded for Apus apus in England (Gladwin
and Nau, 1964) with sharp decreases in body weight being corre
lated with prolonged cold or rainy weather. Such weather greatly
decreases the aerial food supply of these swifts (Lack and Owen,
1955). There was no marked seasonal change in weight between
April and November in either C. brachyura or C. rutilus as is
typical of migrant swifts, particularly C. pelgica in temperate
North America (Coffey, 1958).

FOOD AND FEEDING HABITS
A poorly known aspect of swift biology is their feeding
habits. Although some information exists on the types of food
collected and the rate at which it is brought to the young,
there is only fragmentary information on where and at what rate
it is collected.
In Trinidad, particularly during clear, sunny weather,
mixed flocks of swifts are commonly seen moving up and down the
valleys of the northern range, overhead at one instant, several
miles away in a matter of minutes and back overhead shortly
thereafter. During the summer rainy season these birds are often
observed on the advancing edge of one of the intermittent
showers so abundant at that time of the year. The flocks may.
contain up to seven of the nine species of swifts recorded in
Trinidad. These are only temporary associations, and if the
birds are observed over longer periods certain specific feeding
patterns can be seen.
Chaetura brachyura is by far the most widely distributed
species in Trinidad and is observable at almost all elevations.
It is the only Chaetura that regularly forages over the savanna
areas and is decidedly more abundant there and over the lower
parts of the northern range than over areas above 1200 feet
elevation. One pair feeding young in a nest at an elevation of
500 feet in Arima Valley "used to fly off down the valley in the
70

71
direction of the savanna three miles away. They would return
from the same direction" (Snow, 1962).
Cypseloides rutilus was less often observed in flight and
then only in the upper part of Arima Valley or over the higher
parts of the northern range. Even though it nests in caves at
sea level on the north coast and at elevations of 500-1100 feet
in Arima Valley, it seems to forage exclusively over the forest
at higher elevations. Although the feeding ranges of the two
species overlap at the lower elevations around 500 feet, C.
rutilus is also comidonly observed at higher elevations including
the summit of El Tuchuche (3,068 feet), whereas C. brachyura
is uncommon above 1200 feet. Conversely, I have never observed
C. rutilus over the savanna areas where C. brachyura is abundant.
In addition to feeding at higher elevations, C. rutilus and
another swift, Panyptila cayennensis (Gmelin), appear at all
elevations to feed at greater distances above the ground than
most species of Chaetura. This habit was also observed for C.
rutilus in Trinidad (Snow, 1962) and for C. niger in Washington
(Rathbun, 1925). As this characteristic of feeding at higher
altitudes was most commonly noted during fine weather and
particularly when both C. rutilus and cayennensis were part
of mixed flocks containing one or more species of Chaetura, it
may be less characteristic of their day to day feeding activities
when not in association with other species.
In England, Apus apus generally feeds in the immediate
vicinity of the nests (Lack and Owen, 1955), whereas Cypseloides
niger makes daily trips of several miles from mountain nesting

72
areas to lowland feeding areas in Washington (Rathburn, 1925).
During the breeding season both species also make long-range
movements of several hundred miles to avoid prolonged adverse
weather conditions (Lack, 1955; Udvardy, 1954). Chaetura pelgica
in New York was seen foraging over a field about 1/4 mile from
the nest and regularly brought in Ephemeroptera, presumably
collected over a stream 1/8 mile away. Itoo color-marked birds
were also seen foraging 2 3/4 and 4 miles, respectively, from
their nests (Fischer, 1958).
Weather-influenced differences in the height of feeding
have been noticed for Apus apus and C. niger, which feed higher
in the air on sunny days and low over the ground or water during
rainy or cloudy weather (Lack and Owen, 1955; Rathbun, 1925).
Day to day variations in feeding habits have been noticed
for many species of swifts as they exploit temporary abundances
in their air-born insect prey. They do not merely fly through
the air, mouths open, catching only whatever happens to get
scooped up. If closely observed, swifts can be seen to change
their flight direction to snap up an attractive prey item.
Confirmation of this is provided by the comparison of food
samples with random samples of aero-plankton. The swift-
gathered samples are clearly richer in the larger species
which are less characteristic of true aero-plankton (Lack, and
Owen, 1955).
The foraging habits of C. brachyura and C. rutilus did
not change noticeably from day to day although the swifts often
descended to nearly ground level during wet weather to feed on

73
the large flights of winged reproductive termites. Feeding on
this temporary plethora of food was not confined to the swifts.
Numerous species, ranging in size from house wrens (Troglodytes
aedon) to caciques (Psarocolius decumanus), also preyed on them.
A similar array of birds was noted feeding on termite swarms
in Panama (Eisenmann, 1961). On several occasions I observed
Chaetura brachyura to bank sharply up and flutter briefly near
the outermost branches of trees extending above the forest
canopy. It appeared that the birds were picking insects or
spiders off the leaves. Similar foraging behavior was noticed
for C. pelgica (Fischer, 1958) and may be widespread among
swifts.
Other swifts have been observed feeding in several less
typical ways. Apus apus has been noticed landing on the wall
of a house and gathering spiders under the eaves (Meikeljohn,
1928), and foraging for insects and perhaps nest parasites in
old swallow nests (Gilbert, 1944).
The stomach contents of the swifts collected during this
study were mostly masses of partially digested, poorly identifiable
insect remains. On the other hand, the food brought to the nest
lings was easily identified and probably consisted of the same
food consumed by the adults. The adults brought the food for
the young swifts to the nest in their throat as a compact mass
of undigested insects partially glued together by saliva. A
total of 21 samples of the food brought to nestlings was collected,
17 from C. brachyura and 4 from C. rutilus. These samples were
manipulated from the throat of recently fed nestlings. This

74
method, used earlier by Lack and Owen (1955), did not injure the
the birds if done carefully and was not repeated frequently
enough to disrupt the pattern of normal growth.
The contents of these samples were extremely varied
(Table 10). Eight were homogeneous masses of either winged
ants or winged termites. Heterogeneous samples varied from one
or two types of insects to a mixture of some forty species
representing six orders of insects and nine families of spiders.
The samples varied in size from a nearly complete food ball of
326 insects to only a few remnants of a meal. Since it was not
always possible to get complete food balls from the young birds,
no comparison was made between the number or weight of food items
brought in different trips. In four cases it was possible to get
food samples from two C. brachyura nestlings of a single brood
on a single visit to the nest. In each case both nestlings had
received similar food. In the one case where samples were ob
tained on the same day from C. brachyura nestlings of different
broods in nest sites about a mile apart, one nestling had re
ceived a homogeneous sample of winged ants while two nestlings
at the other site had both received mixed samples of Diptera,
Coleptera, and Hymenoptera. Day to day variation in the food
brought in by a single pair of adults was extensive and usually
included both homogeneous and heterogeneous samples. No analysis
of seasonal differences in food items was possible since these
samples could only be collected while there were young birds in
the nest.
Interspecific differences in the type of food collected

75
Table 10. Contents of food balls collected from nestlings of
Chaetura brachyura and Cypseloides rutilus.
Food item
Number of
samples in which
it occurred
Number of
individuals
A.
Araneae
Chaetura brachyura
2
94
Lycosidae
1
1
Tetragnathidae
1
1
Linyphiidae
1
1
Clubionidae
1
12
Mi c ryph an ti dae
1 '
2
Oxyopidae
1
2
Thomisidae
1
16
Salticidae
1
34
Theridiidae
1
1
Araneidae
1
3
unidentified
1
21
Coleptera
6
73
Curculionidae
3
14
Apion sp.
1
1
Ceutorhynchus sp.
1
12
unidentified
1
1
Scolytidae
3
9
Cocotrypes sp.
2
7
unidentified
2
2
Cryptophagidae
1
2
Chrysomelidae
3
13
Lema sp.
1
3
Chaetocnema sp.
1
2
Systena sp.
2
2
Altica sp.
1
2
unidentified
1
4
Platypodidae
3
28
Platypus sp.
3
28
Staphylinidae
2
3
Coccinellidae
1
1
Nitidulidae
3
3
Stelidota sp.
1
1
Garpophilus sp.
2
2
Orthoptera
1
1
Hemiptera
2
10
Saldidae
1
1
Tingidae
1
9

-Table 10 (Continued)
Number of
samples in which Number of
Food item it occurred individuals
Homoptera
2
16
Membracidae
1
2
Aphidae
1
1
Cicadellidae
1 -
5
Deltocephalus flavicosta
1
1
unidentified
1
4
Delphacidae
2
8
Peregrinus maidus
1
1
Sonata sp.
1
1
unidentified
1
6
Diptera
12
402
Hymenoptera
16
203
Formicidae
12
128
Camponotus sp.
6
41
Trachymyrmex sp.
2
6
Leptalae elongata
2
15
unidentified
4
75
Isoptera
4
49
Kalotermitidae
1
1
Calcaritermes nigriceps
1
1
Rhinotermitidae
2
32
Coptotermes testareus
2 2
32
Termitidae
1
16
Nasutitermes costalis
1
16
B. Cypseloides
Hymenoptera
rutilus
2
19
Formicidae
2
19
Dorymyrmex sp.
2
19
Isoptera
2
25
Rhinotermitidae
1
20
Dolichorhinotermes longilabius
1
20
Termitidae
1
5
Anoplotermes meridianus
1
2
Anoplotermes sp.
1
3

77
by these swifts is hard to assess accurately because of the
difficulties encountered in collecting sufficient food samples
from C. rutilus. A great variety of food items was utilized by
C. brachyura in apparent contrast to C. rutilus. This difference
is probably due to the accidental collection of nearly homogeneous
samples of winged ants and termites from C. rutilus, and it is
possible that additional samples would have shown a diversity of
prey items equal to that of C. brachyura. Homogeneous food
samples have been reported for several other species of swifts,
and in no case were they typical of the normal day to day diet.
Thus they are only further indications of what has already been
observed from the foraging behavior: swifts are quick to feed
on any temporarily abundant prey items, like mayflies
(Ephemeroptera) or aphids (Homoptera: Aphidae) in temperate
areas or winged ants (Hymenoptera: Forraicidae) and termites
(Isoptera) in the tropical areas.
Not only do swifts feed on many different kinds of
insects but also on a variety of sizes. Even so there seem
to be certain limits to the sizes of prey items taken by any
species of swift. The upper limit probably depends upon the
size of the bird and what it could comfortably swallow.
All food items of C. brachyura and C. rutilus were
measured to check for possible size differences in their prey.
The total length from the head to the tip of the abdomen, ex
clusive of antennae and legs, was taken as the best available
indication of total size. All fractional measurements were read
to the next whole millimeter. The range of sizes and abundance

78
of each size food item is shown in Fig. 13. As was true for
the prey species diversity, C. brachyura appears to feed on a
wider range of prey items than C. rutilus. Again it seems likely
that this seeming difference is an artifact of the sampling. If
only the similar food items (winged ants and termites) of the
two swift species are compared (Fig. 15), the interspecific dif
ferences in the size of prey selected are not significant.
Winged ants and termites appear in the food samples throughout
the breeding season, and the absence of any difference in size
of these food items selected by the swifts may indicate a similar
absence of difference in size of other food items selected. If
so, C. rutilus and C. brachyura would appear to select similar
kinds and sizes of food items, although their foraging ranges
J
only partially overlap.
In England, Apus apus usually takes food items ranging
in size from 2-10 mm, rarely larger or smaller. Within this
range it tends to take larger items from 5-8 mm long during fine
weather when insects are abundant. During rainy or cold weather
there are fewer insects available of all sizes, and the swift
includes more of the smaller prey items from 2-5 mm in its diet
(Lack and Owen, 1955).
From this it seems that larger species, such as Apus
apus, may occasionally select food items larger than any taken
by either C. brachyura or C. rutilus and rarely take prey as
small as some regularly taken by these smaller swifts. Similarly,
276 food items collected by another large swift, Cypseloides
niger, in Veracruz, Mexico, ranged from 2-12 mm in length, with

Fig. 15. Size of prey selected by Chaetura brachyura and Cypseloides rutilus.
Diagonal shaded areas represent the portion of the sample consisting of winged
ants and termites. .
vO

80
the most frequent sizes being 9 and 10 mm, or about the maximum
size recorded for either C. brachyura or C. rutilus (Collins,
unpubl.). If extended to other situations, two species of
similar size would expectedly feed on insects within similar
size ranges. The food habits of Apus apus and A. pallidus
(Shelley) support this idea. These two swifts are nearly equal
in size and select similar sized prey items (G. E. Watson, pers.
comm.).

* BHPHHgnHjB r-v
FEEDING OF YOUNG
The feeding of the nestlings was seen on several occasions
but never close enough to be sure of details. Presumably it is
similar to that reported for other swifts in that the adult
carries the food to the nest in the mouth or throat. The adult
inserts its bill into the mouth of the nestling and passes the
food to it. As brought to the nest, the food items are often
glued together with saliva forming a compact wad or "food ball."
Very young birds generally receive only part of a ball of food,
the rest being shared with other nestlings or retained by the
adult. When older, a single nestling usually receives the entire
food ball.
The rate of feeding of C. brachyura is similar to that of
other species of Chaetura for which there is information. The
intervals between visits of adults to the nest range from 2.5-
45 minutes and average 20.5 minutes.
Like other swifts of the genus, Cypseloides rutilus is
characteristically absent from the nest for extended periods of
time particularly after brooding had ended. The feeding inter
vals of C. rutilus are irregular and lengthy. The one interval
for which an exact time was obtained was 36 minutes. All other
intervals recorded were in excess of 100 minutes, although the
exact duration was not determined.
81

82
The best studied species of Cypseloides, C. niger, may
leave the nest at dawn and not return to feed the nestling until
nearly dusk (Smith, 1928). Some feedings have been observed in
the morning hours and indicate higher feeding rates at some
times, possibly when the nestling is very young. Occasionally,
an adult of this species has been observed to feed the nestling,
brood it, and then regurgitate a second meal for the young swift
several hours after the initial feeding (Michael, 1927). Two
adults collected at night at their roosts still had large amounts
of food in their throats, which would have enabled them to feed
the nestling a second time (Collins, unpubl.).
The most complete information is that for Apus affinis
in Kenya (Moreau, 1942b). This swift fed the young birds at
intervals ranging from less than 8 to 254 minutes but averaged
one feeding trip every 118 minutes for a brood of two. Broods
of one were fed at a slower rate and broods of three at a
significantly faster rate than either the broods of one or two.
Despite acceleration of feeding rate with increased brood size,
the rate per individual nestling decreased in larger broods.
In many species a flurry of feeding activity begins
shortly before evening roosting, with the adults making many
trips to the nest in a short period of time. Both Fischer
(1958) and Sherman (1952), however, found that C. pelgica
brought smaller quantities of food per trip during such visits,
occasionally only a single insect.
An increase in rate of feeding with increasing age of
the nestlings is indicated in some swifts (Kendeigh, 1952i97-98).

83
This is particularly true in times of good weather and an
abundance of food, when the young swifts tend to build up large
reserves of subcutaneous fat. Lack (1956c) noticed a tendency
for adults to stay away from the nest for longer periods when
the young were well fed and consequently did not beg as en
thusiastically when adults returned with food.

MOLT
The pattern of molt in both C. brachyura and C. rutilus
is similar and is in agreement with the general sequence of molt
outlined for species of Chaetura (Snow, 1962)* The annual molt
starts with the primaries, which are replaced in sequence from
the innermost outward. The secondaries begin to be replaced
after the primary molt is well advanced. The replacement of the
tail is centripetal and begins after the wing molt has reached
about the fourth or fifth primary. Body molt begins soon after
the start of the primary molt and spans the whole duration of
the molting period. It starts in the head and neck regions and
progresses posteriorly over the body, a bit more rapidly on the
dorsum than on the venter.
Juvenile birds do not molt either remiges or rectrices
during the first fall. Some light body molt was observed in
these birds during late September and October which may repre
sent a partial postjuvenal molt of the body feathers.
84

PARASITES AND PREDATORS
Ectoparasites in the form of mites (Acaria) and
feather lice (Mallophaga) were collected from both species.
Mallophagans were particularly abundant on nestlings during the
period when their feathers were first emerging from the sheath.
Mallophagan eggs were most abundant on the dorsal feathering of
the head and neck. Mites were noticed only on the feathers of
the wings, particularly on the vanes of the outer primaries.
Although these collections have not yet been identified, the
*
mallophagan species Dennyus brevicapitis has been reported from
C. brachyura in Trinidad, and Dennyus brunneitorques and Bureum
yepezi from C. rutilus in other parts of its range (Carriker,
1954, 1958).
One specimen of a flea, Polygenis dunni, was caught on a
young nestling of C. brachyura. This species has previously
been collected from several rodents in Trinidad and northern
South America (Johnson, 1957).
The only endoparasites observed were tapeworms (Taenia
sp.) collected from the intestines of both swifts.
Adult mortality in swifts is generally lower than in
smaller and slower-flying species of passerines (Lack, 1954).
No predators of adult swifts were observed during this study.
In Venezuela, Beebe (1950) noted a pair of nesting bat falcons
85

86
(Falco rufigularis) preying heavily on swifts, particularly
the smaller species including C. brachyura and C. rutilus.

DISCUSSION
In their general biology Chaetura brachyura and
Cypseloides rutilus appear similar to most swifts for which
information is available. They are almost exclusively aerial
in their activities and feed on air-borne arthropods, mostly
insects.
The breeding season of both swifts coincides with the
abundance of aerial food associated with the summer rainy season.
Many other species of Trinidadian birds have similarly altered
their reproductive cycles so that breeding occurs at a time of
maximal abundance of suitable food. For the swallows, as for
the swifts, the peak in breeding and the maximal abundance of
food both occur early in the rainy season. For the nectar
feeding hummingbirds and the bananaquit (Coereba flaveola), how
ever, the maximal food abundance and the peak in breeding occurs
at the height of the dry season (December-May) at the time when
many forest trees and vines are in flower (Snow and Snow, 1964).
The absence of a pronounced peak in food abundance may result in
an extended breeding season as in two" species of thrushes (Snow
and Snow, 1963). Beyond the tropics, a similar adaptive rela
tionship often exists between breeding season and maximal food
abundance, as in temperate zone tits of the genus Parus and
arctic sandpipers of the genus Calidris (Gibb, 1954; Holmes,
1966).
87

88
The pattern of nestling growth in both species is
typical of altricial birds, although greatly prolonged as com
pared to the several small passerines reviewed by Maher (1964).
Snow (1962) suggests that the inaccessibility of the nest has
caused a relaxation of selection for the accelerated growth of
nestlings so typical of most passerine birds nesting in the open.
Chaetura brachyura shows a pronounced similarity in all
aspects of its biology to all other New World species of Chaetura
that have been studied. In nest form, clutch size, nestling
growth pattern, feeding habits, and general behavior only minor
specific differences exist. For the most part these result from
the timing of events during development rather than being major
departures from the common pattern. This general similarity is
shown by an array of species which inhabit the area from temperate
North America south to subequatorial South America, and also
includes both sedentary and migratory species.
An equal degree of similarity exists between Cypseloides
rutilus and other congeneric species, although the little informa
tion available relates mainly to C. nlger.
Although both species studied show similarities to various
congeners, several pronounced intergeneric differences occur in
their reproductive activities. The nest site of C. rutilus is
colder and darker than that of C. brachyura. It is also less
accessible to predators and there are reduced losses of both
eggs and nestlings of C. rutilus. At the same time this environ
ment imposes several demands upon these swifts as a part of the
young. The newly hatched young swift has a very poorly developed

89
capacity for temperature regulation, which improves slowly
during the first weeks of nestling life. If left unbrooded in
the cold environment of the nest, C. rutilus nestlings would
rapidly lose heat to the environment, and much of the energy
available for growth would be expended in wasteful thermogenesis.
To prevent such energy-draining heat loss, the adults brood the
nestlings until their capacity for thermoregulation has reached
a stage where the amount of heat lost without brooding will no
longer appreciably slow further growth and development. In C.
rutilus and other congeners the development of thermoregulation
is aided by the early appearance of an insulating feather coat.
This insulation includes the normal contour feathers, which
break out of the sheath at an early date, as well as a down-like
semiplume portion of the first teleoptile plumage, which also
grows in rapidly. Thus the intergeneric differences in nest
ling development and adult behavior represent adaptations that
enable CL rutilus and other species of Cypseloides to contend
with the cold environment of the nest site.
The regulation of clutch size in birds has been studied
in diverse taxa in many parts of the world. The most complete
information is based on studies of temperate passerine species in
which the clutch size "has been adapted by natural selection to
correspond with the largest number of young for which the parents
can, on the average, provide enough food" (Lack, 1954:31).
Studies on Old World temperate and tropical swifts have shown
these birds to be similarly food limited with their clutch size
adapted to the number of young which can be raised under average

90
conditions (Lack and Lack, 1951; Lack and Am, 1947; Perrins,
1964; Moreau, 1941, 1942a, 1942b). There seems to be no reason
to doubt that other swifts in both temperate and tropical parts
of the New World are similarly food limited and have their
clutch size regulated by the same factors.
As shown in this study, clutch size of C. brachyura
resembles that of other species of Chaetura and is nearly double
the clutch size of Cypseloides rutilus. It would thus seem that
in Trinidad C. rutilus is capable of obtaining enough food to
nourish only two young, while C. brachyura can gather nearly
double that amount. As noted earlier only a partial overlap of
the feeding range of these swifts occurs with C. rutilus feeding
at higher elevations and also at higher altitudes. Even so, it
is hard to accept the view that the food decreases in abundance
by nearly 50 per cent with such shifts in feeding ecology and
hence is entirely responsible for the reduction of clutch size in
C. rutilus. It is equally hard to accept that C. rutilus is only
half as efficient at food gathering as C. brachyura. As noted
earlier, however, C. rutilus broods the young more continuously
and for a longer time than C. brachyura in order to contend with
the cold environment of its nest site. At such times C. rutilus
reduces the food supply available to its young by reason of the
restriction of foraging to but one adult at a time. The absolute
abundance of food may be the same or only slightly diminished in
its foraging range, but the effective food supply available to
the nestlings is much less. The combination of such reduction
in effective food supply, mainly through reduced foraging capacity,

91
could be responsible for the smaller clutch size observed for
C. rutilus.
In other species of Cypseloides a clutch size of two is
typical, with the exception of C. niger. This species, which
nests in extremely cold environments at high elevations in the
temperate zone, also has to contend with a less dependable food
supply owing to prolonged periods of bad weather in its breeding
area. Like other swifts facing similar conditions it shows a
further reduction in clutch size, namely to a single egg. It
would be interesting to know what the clutch size of this bird
is when nesting in less rigorous environments as in parts of
Central America.
Snow (1962) suggested that the small size of C. rutilus
nests provides room for only two nestlings with consequent
selection for a clutch of only two. This seems doubtful unless
a maximum ne§t sis for Cypselaldas can be demonstrated. It
also seems unlikely since Cypseloides semicollaris builds no
nest and lays only two eggs (Rowley and Orr, 1962).
In their feeding, C. brachyura and C. rutilus apparently
select food items within the same range of sizes, but forage
in slightly different areas. This may well represent an efficient
mechanism to avoid interspecific competition between similarly
sized swifts. As noted earlier, differently sized swifts tend
to select different sizes of prey items. Thus where two dif
ferently sized species share a foraging range the size differences
in the food items selected may be sufficient to avoid interspecific
food competition. In support of this hypothesis it would be

92
extremely valuable to know the range in size of prey items
selected by an extremely large species as Cypseloides
semicollaris or C. zonaris, and any of the tiny species of -
Collocalia or Micropanyptila furcata Sutton.
Feeding at higher altitudes above the ground may also
represent an adaptive divergence of foraging behavior that
further reduces interspecific competition within any given
foraging range. In addition to C. rutilus and P. cayennensis,
which exhibit this habit in Trinidad, Collocalia maxima Hume
similarly forages at higher altitudes and specializes on the
larger higher-flying insects in Malaysia (Medway, 1962a). It
thereby reduced interspecific competition with the several
other Malaysian species of Collocalia.

SUMMARY
The comparative biology of the short-tailed swift,
Chaetura brachyura, and the chestnut-collared swift, Cypseloides
rutilus, was studied in Trinidad during parts of 1962-1964. In
many respects both species were similar to congeners for which
information exists.
Both swifts breed during the rainy season when insect
food is abundant, but their breeding activities are triggered
by different proximate factors.
C. brachyura lays a clutch averaging 3.8 eggs in nests
of twigs cemented to the walls of manholes. C. rutilus, which
lays a clutch of 2 eggs, builds nests of mosses, lycopsids, and
ferns on rocky outcrops over rivers and mountain streams, and
occasionally in sea caves. The environmental temperature of nest
sites of C. rutilus is lower than for those of C. brachyura,
and the nestlings of C. rutilus are brooded longer and more
continuously than nestlings of C. brachyura. C. rutilus has
a lower mortality of eggs and young than C. brachyura, the nest
sites of C. rutilus being, presumably, less accessible to preda
tors.
The young of C. brachyura grow more rapidly than those
of C. rutilus, but both species perfect their capacity for
thermoregulation at about the same rate. In C. rutilus, however,
93

94
a down-like semiplume portion of its 'first teleoptile plumage
emerges at an early age and aids in thermoregulation.
The young of C. brachyura leave the nest when about 3
weeks old and hang on the walls of the nest cavity until fledging
at the age of 4-5 weeks. C. rutilus young remain in the nest un
til fledging at an age of 5-6 weeks.
These two swifts appear to feed on the same types and
sizes of aerial food. Their foraging ranges, however, only
partially overlap. C. rutilus feeds at higher elevations than
C. brachyura and to some extent also at higher altitudes. The
differences in foraging ranges may be an adaptation enabling them
to avoid interspecific competition for food. Similar adapta
tions seem to be present in other species of swifts.
. Most of the differences in the biology of these two
species of swifts are associated with reproduction and represent
adaptations of C. rutilus to the cool, damp environment of the
nest site.

LITERATURE CITED
Amadon, Dean
1936. Chimney swifts nesting in a bam. Auk, 53:216-217.
Baldwin, Paul H., and William F. Hunter
1963. Nesting and nest visitors of the vaux's swift in
Montana. Auk, 80:81-85.
Baldwin, Paul H., and Nick K. Zaczkowski
1963. Breeding biology of the vaux swift. Condor, 65:400-406.
Bartholomew, Geo. A., Thomas R. Howell, and Tom J. Cade
1957. Torpidity in the white-throated swift, anna hummingbird,
and poorwill. Condor, 59:145-155.
Beard, J. S.
1946. The Natural Vegetation of Trinidad. Clarendon Press,
Oxford. 152 pp.
Beebe, William
1950. Home life of the bat falcon, Falco albigularis
albigularis Daudin. Zoolgica, 35:69-86.
1952. Introduction to the ecology'of the Arima Valley,
Trinidad, B.W.I. Zoolgica, 37:157-183.
Belcher, Charles, and G. D. Smooker
1936. Birds of the colony of Trinidad and Tobago. Part
III. Ibis, 6:1-35.
Bendire, Charles E.
1895. Life histories of North American birds. U. S. Nat.
Mus., Special Bull. No. 3:177-183.
95

96
Bent, Arthur C.
1940. Life histories of North American cuckoos, goatsuckers,
hummingbirds and their allies. Bull. U. S. Nat. Mus.,
176:1-506.
Brody, S.
1945. Bioenergetics and Growth. Reinhold Publ. Co., New
York. 1023 pp.
Carriker, M. A., Jr.
1954. Studies in Neotropical Mallophaga, XI: bird lice of
the suborder Amblycerca, genus Dennyus Neumann. Proc.
U. S. Nat. Mus., 103:533-549.
1958. A new species and subspecies of Mallophagan from
Venezuela. Acta Biol. Venezuela, 2:171-177.
Coffey, Lula C.
1958. Weights of some chimney swifts at Memphis. Bird-
Banding, 29:98-104.
Collins, Charles T.
1963. The "downy" nestling plumage of swifts of the genus
cypseloides. Condor, 65:324-328.
1965. The down-like nestling plumage of the palm swift
Cypsiurus parvus (Lichtenstein). Ostrich, 36:201-202.
Dawson, William R., and Francis C. Evans
1957. Relation of growth and development to temperature
regulation in nestling field and chipping sparrows.
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329-340.
Dexter, Ralph W.
1952. Extraparental cooperation in the nesting of chimney
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1951. A nest of Chaetura vauxi richmondi in central Honduras.
Wilson Bull., 63:201-202.

97
Eisenmann, Eugene
1961. Favorite foods of neotropical birds: flying termites
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1962. A new species of swift of the genus Cypseloides from
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1944. Swifts scavenging in house-martin's nests. Brit.
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Gladwin, T. W., and B. S. Nau
1964. A study of swift weights. Brit. Birds, 58:344-356.
Gibb, John
1954. The breeding biology of the great and blue titmice.
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Haverschmidt, F.
1958. Schornsteine als Massenschlafplatz von Chaetura brachyura
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Holt, E. G.
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98
Hunter, William F., and Paul H. Baldwin
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Johnston, David W.
1958. Sex and age characters and salivary glands of the
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Kahl, M. Philip, Jr.
1962. Bioenergetics of growth in nestling wood storks.
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1952. Parental care and its evolution in birds. Illinois
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Knorr, Owen A.
1961. The geographical and ecological distribution of the
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1962. Black swift breeds in Utah. Condor, 64:79.
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1950. The life of the swift, Micropus apus (L.), in relation
to the weather. Ann. Acad. Sci. Fenn., 15:1-151.
Lack, David
1954. The Natural Regulation of Animal Numbers. Clarendon
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1956a. A review of the genera and nesting habits of swifts.
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99
1956b. Further notes on the breeding biology of the swift
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1956c. Swifts in a Tower. Methuen and Co., London. 239 pp.
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1947. Die Bedeutung der Gelegegresse beira Alpensegler.
Omith. Beob., 44:188-210.
Lack, David, and Elizabeth Lack
1951. The breeding biology of the swift, Apus apus. Ibis,
93:501-546.
1952. The breeding behaviour of the swift. Brit. Birds;
45:186-215.
Lack, D., and D. F. Owen
1955. The food of the swift. Journ. Animal Ecology. 24:
120-136.
Legg, Ken
1956. A sea-cave nest of the black swift. Condor, 58:183-187.
Maher, William J.
1964. Growth rate and development of endothermy in the snow
bunting (Plectrophenax nivalis) and lapland longspur
(Calcarius lapponicus) at Barrow, Alaska. Ecology,
45:520-528.
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1956. Fhotostimulation of an equatorial bird (Quelea quelea,
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Marshall, A. J., and S. J. Folley
1956. The origin of nest cement in edible-nest swiftlets
(Collocalia spp.). Proc. Zool. Soc. London, 126:383-
389.
Medway, Lord
1961. The identity of Collocalia fuciphaga (Thunburq). Ibis,
103:625-626.
1962a. The swiftlets (Collocalia) of Niah Cave, Sarawak.
Part I, Breeding biology. Ibis, 104:45-66.

100
1962b. The swiftlets (Collocalia) of Niah Cave, Sarawak.
Part II, Ecology and regulation of breeding. Ibis,
104:228-245.
1962c. The relation between the reproductive cycle, moult,
and changes in the sublingual salivary glands of the
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Lond., 138:305-315.
Meikeljohn, A. H.
1928. Swifts taking food from under eaves. Brit. Birds,
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Michael, Charles M.
1927. Black swift nesting in Yosemite National Park. Condor,
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1933. A young black swift. Condor, 35:30.
Miller, Alden H.
1959. Response to experimental light increments by andean
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1941. A contribution to the breeding biology of the palm
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1942a. The breeding biology of Micropus caffer streubelii
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1871. Notes on some birds in the museum of Vassar College.
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Parkes, Kenneth C., and George A. Clark, Jr.
1964. Additional records of avian egg teeth. Wilson Bull.,
76:147-153.

101
Perrins, Christopher
1964. Survival of young swifts in relation to brood size.
Nature, 201:1147-1148.
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1925. The black swift and its habits. Auk, 42:497-516.
Reboratti, J. H.
1918. Nidos y huevos de vencejos. Homero, 1:193.
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Rowley, J. Stuart, and Robert T. Orr
1962.
1965.
Schmidt,
1965.
Sherman,
1952.
Sick, H.
1948a.
1948b.
1959.
Sims, R.
1961.
Skutch,
1961.
The nesting of the white-naped swift. Condor, 64:
361-367.
Nesting and feeding habits of the white-collared swift.
Condor, 67:449-456.
Rudolf K.
Brutbiologie des weiss Burzelseglers Apus caffer caffer
(Lichtenstein) auf der Kaphalbinsel. Joum. f. Ornith.
106:295-306.
Althea R.
Birds of an Iowa Doryard. Ihe Christopher Pub. House,
Boston. 270 pp.
The nest of Chaetura andrei meridionalis. Auk., 65:
515-520.
The nesting of Reinarda squamata (cassin). Auk., 65:
169-174.
Notes on the biology of two Brazilian swifts, Chaetura
andrei and Chaetura cinereiventris. Auk., 76:471-477.
W.
The identification of Malaysian species of swiftlets
Collocalia. Ibis, 103a:205-210.
Alexander F.
Helpers among birds. Condor, 63:198-226.

102
1964. Life histories of hermit hummingbirds. Auk., 81:5-25.
Smith, Emily
1928. Black swifts nest behind a waterfall. Condor, 30:
136-138.
Snow, David W.
1962. Notes on the biology of Trinidad swifts. Zoolgica,
47:129-139.
Snow, David W., and Barbara K. Snow
1963.
Breeding and the annual cycle in three Trinidad
thrushes. Wilson Bull., 75:27-41.
1964.
Breeding seasons and annual cycles of Trinidad
land-birds. Zoolgica, 49:1-39.
Sutton, George M.
1948.
Breeding of Richmonds swift in Venezuela. Wilson
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Todd, W.
E., and M. A. Carriker, Jr.
1922.
The birds of the Santa Marta region of Colombia: A
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14:1-611.
Tordoff, Harrison B., and William R. Dawson
1965.
The influence of daylength on reproductive timing in
the red crossbill. Condor, 67:416-422.
Udvardy,
Miklos D. F.
1954.
Summer movements of black swifts in relation to weather
conditions. Condor, 56:261-267.
Weitnauer, Emil
1947. Am Neste des Mauerseglers, Apus apus apus (L.)
Ornith. Beob., 44:133-182.

BIOGRAPHICAL SKETCH
Charles Thompson Collins was bom on March 9, 1938,
at Long Branch, New Jersey. In June 1956 he was graduated
from the Pingry School, in Elizabeth, New Jersey. He received
the degree of Bachelor of Arts from Amherst College in June
1960, and the Master of Science degree from The University of
Michigan in June 1962. Since then he has worked toward the
degree of Doctor of Philosophy at the University of Florida.
He is a member of the Society of the Sigma Xi, Ameri
can Ornithologists' Union, Cooper Ornithological Society,
Wilson Ornithological Club, and Urner Ornithological Club.
103

This dissertation was prepared under the direction of
the chairman of the candidates supervisory committee and has been
approved by all members of that committee. It was submitted to
the Dean of the College of Arts and Sciences and to the Graduate
Council, and was approved as partial fulfillment of the require
ments for the degree of Doctor of Philosophy.
June 21, 1966
Dean,
Supervisory Committees
Rehuir
Dean, Graduate School



LITERATURE CITED
Amadon, Dean
1936. Chimney swifts nesting in a bam. Auk, 53:216-217.
Baldwin, Paul H., and William F. Hunter
1963. Nesting and nest visitors of the vaux's swift in
Montana. Auk, 80:81-85.
Baldwin, Paul H., and Nick K. Zaczkowski
1963. Breeding biology of the vaux swift. Condor, 65:400-406.
Bartholomew, Geo. A., Thomas R. Howell, and Tom J. Cade
1957. Torpidity in the white-throated swift, anna hummingbird,
and poorwill. Condor, 59:145-155.
Beard, J. S.
1946. The Natural Vegetation of Trinidad. Clarendon Press,
Oxford. 152 pp.
Beebe, William
1950. Home life of the bat falcon, Falco albigularis
albigularis Daudin. Zoolgica, 35:69-86.
1952. Introduction to the ecology'of the Arima Valley,
Trinidad, B.W.I. Zoolgica, 37:157-183.
Belcher, Charles, and G. D. Smooker
1936. Birds of the colony of Trinidad and Tobago. Part
III. Ibis, 6:1-35.
Bendire, Charles E.
1895. Life histories of North American birds. U. S. Nat.
Mus., Special Bull. No. 3:177-183.
95


96
Bent, Arthur C.
1940. Life histories of North American cuckoos, goatsuckers,
hummingbirds and their allies. Bull. U. S. Nat. Mus.,
176:1-506.
Brody, S.
1945. Bioenergetics and Growth. Reinhold Publ. Co., New
York. 1023 pp.
Carriker, M. A., Jr.
1954. Studies in Neotropical Mallophaga, XI: bird lice of
the suborder Amblycerca, genus Dennyus Neumann. Proc.
U. S. Nat. Mus., 103:533-549.
1958. A new species and subspecies of Mallophagan from
Venezuela. Acta Biol. Venezuela, 2:171-177.
Coffey, Lula C.
1958. Weights of some chimney swifts at Memphis. Bird-
Banding, 29:98-104.
Collins, Charles T.
1963. The "downy" nestling plumage of swifts of the genus
cypseloides. Condor, 65:324-328.
1965. The down-like nestling plumage of the palm swift
Cypsiurus parvus (Lichtenstein). Ostrich, 36:201-202.
Dawson, William R., and Francis C. Evans
1957. Relation of growth and development to temperature
regulation in nestling field and chipping sparrows.
Physiol. Zool., 30:315-327.
1960. Relation of growth and development to temperature
regulation in nestling vesper sparrows. Condor, 62:
329-340.
Dexter, Ralph W.
1952. Extraparental cooperation in the nesting of chimney
swifts. Wilson Bull., 64:133-139.
Dickinson, J. C., Jr.
1951. A nest of Chaetura vauxi richmondi in central Honduras.
Wilson Bull., 63:201-202.


TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS i i
LIST OF TABLES v
LIST OF ILLUSTRATIONS vi
INTRODUCTION 1
STUDY AREA 3
METHODS AND MATERIALS 5
GENERAL DESCRIPTION 8
RANGE 10
NESTS AND NEST SITES 11
Chaetura brachyura 11
Cypseloides rutilus ............. 18
BREEDING SEASONS 27
CLUTCH SIZE 33
INCUBATION
PARENTAL CARE 41
Chaetura brachyura 41
Nestling period. ..... .. 41
Fledgling period 41
Cypseloides rutilus ........... 42
BROODING 44
FLEDGING SUCCESS 45
GROWTH
Body weight 47
iii


60
Fig. 11. Chaetura brachyura nestlings and fledglings,
a) in the nest shortly before leaving, b) on wall near nest.


PARENTAL CARE
The period during which the young are under parental
care is divided into nestling and fledgling periods. The nest
ling period includes the time the young are in the nest. The
fledgling period is when the young are out of the nest but in
capable of flying and are still being fed by the adults. These
periods are quite different in the two species of swifts in this
study. In C. brachyura there is a well defined nestling and
fledgling period while in C. rutilus these two periods overlap..
Chaetura brachyura
Nestling period. The young of C. brachyura spend the
first three weeks of their lives in the nest. Some birds leave
the nest as early as day 20 but most remain in it until 22-23
days after hatching. Those in larger broods tend to leave the
nest sooner than those in smaller ones.
Fledgling period. C. brachyura has a fledgling period
lasting about two weeks during which the young are out of the
nest clinging to the walls of the nest cavity. Most of the
fledglings remain in the nest cavity until they are 30-36 days
old, and occasional individuals stay until they are about 40
days old, even though they may be capable of leaving as early
as 26 days after hatching. In one extreme case two young birds
were still roosting in the nest cavity and being fed by the adults
when 49 and 50 days old, respectively.
41


6
taken with the bulb inserted about 10 mm into the cloaca.
Cold stress experiments were used as a part of the
investigation of nestling thermoregulation. These involved
a 6x8x5 inch cold chamber constructed of 1-1/8 inch thick
foam plastic insulation material (Fig. 1). When equipped with
four 6-oz cans of "Skotch Ice" (refreezable liquid), this
chamber maintained a temperature of approximately 5 C for
several hours. In the field, nestlings were placed individually
in the chamber for a period of 5 minutes, and their temperatures
were recorded before and after cold exposure. Even though
sharp body temperature drops were recorded for very young
nestlings, no ill effects were attributable to this test.
Swifts of both species were yaptured at night roosting
places for weight and molt studies. Flocks of C. brachyura
were generally confined in a roost site and examined the follow
ing morning. A hand net was used to capture C. rutilus adults
roosting in a river gorge in Arima Valley; they were held in
captivity over night and released the following morning.


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Fig. 15. Size of prey selected by Chaetura brachyura and Cypseloides rutilus.
Diagonal shaded areas represent the portion of the sample consisting of winged
ants and termites. .
vO


LIST OF ILLUSTRATIONS
Figure Page
1. Cold chamber used in tests of thermoregulatory
capacity of nestling swifts. .. ... 7
2. Manhole nest sites of Chaetura brachyura 13
3. Nests of Chaetura brachyura 15
4. Nests of Cypseloides rutilus ..... 20
5. Nesting material of Cypseloides rutilus growing
on stream-side rock ledge 22
6. Stream nesting habitat of Cypseloides rutilus. 24
7. Growth curve of Chaetura brachyura ........ 48
8. Growth curve of Cypseloides rutilus 49
9. Growth of the wing of Chaetura brachyura and
Cypseloides rutilus 55
10. Growth of the tail of Chaetura brachyura and
Cypseloides rutilus. ............... 56
11. Chaetura brachyura nestlings and fledglings. ... 60
12. Body temperatures of nestlings of Chaetura
brachyura when unbrooded 63
13. Body temperatures of nestlings of Cypseloides
rutilus when unbrooded ...... 64
14. Decrease in body temperature of nestling swifts
under cold stress. 65
15. Size of prey selected by Chaetura brachyura and
Cypseloides rutilus. ............... 79
vi


24
Fig. 6
SLreara nesting habitat of Cypseloides rutilus


-Table 10 (Continued)
Number of
samples in which Number of
Food item it occurred individuals
Homoptera
2
16
Membracidae
1
2
Aphidae
1
1
Cicadellidae
1 -
5
Deltocephalus flavicosta
1
1
unidentified
1
4
Delphacidae
2
8
Peregrinus maidus
1
1
Sonata sp.
1
1
unidentified
1
6
Diptera
12
402
Hymenoptera
16
203
Formicidae
12
128
Camponotus sp.
6
41
Trachymyrmex sp.
2
6
Leptalae elongata
2
15
unidentified
4
75
Isoptera
4
49
Kalotermitidae
1
1
Calcaritermes nigriceps
1
1
Rhinotermitidae
2
32
Coptotermes testareus
2 2
32
Termitidae
1
16
Nasutitermes costalis
1
16
B. Cypseloides
Hymenoptera
rutilus
2
19
Formicidae
2
19
Dorymyrmex sp.
2
19
Isoptera
2
25
Rhinotermitidae
1
20
Dolichorhinotermes longilabius
1
20
Termitidae
1
5
Anoplotermes meridianus
1
2
Anoplotermes sp.
1
3


77
by these swifts is hard to assess accurately because of the
difficulties encountered in collecting sufficient food samples
from C. rutilus. A great variety of food items was utilized by
C. brachyura in apparent contrast to C. rutilus. This difference
is probably due to the accidental collection of nearly homogeneous
samples of winged ants and termites from C. rutilus, and it is
possible that additional samples would have shown a diversity of
prey items equal to that of C. brachyura. Homogeneous food
samples have been reported for several other species of swifts,
and in no case were they typical of the normal day to day diet.
Thus they are only further indications of what has already been
observed from the foraging behavior: swifts are quick to feed
on any temporarily abundant prey items, like mayflies
(Ephemeroptera) or aphids (Homoptera: Aphidae) in temperate
areas or winged ants (Hymenoptera: Forraicidae) and termites
(Isoptera) in the tropical areas.
Not only do swifts feed on many different kinds of
insects but also on a variety of sizes. Even so there seem
to be certain limits to the sizes of prey items taken by any
species of swift. The upper limit probably depends upon the
size of the bird and what it could comfortably swallow.
All food items of C. brachyura and C. rutilus were
measured to check for possible size differences in their prey.
The total length from the head to the tip of the abdomen, ex
clusive of antennae and legs, was taken as the best available
indication of total size. All fractional measurements were read
to the next whole millimeter. The range of sizes and abundance


Table 6. Average hatching and fledging success of swift species.
Species
Eggs hatched of
No. completely
incubated (%)
Eggs hatched
of No. laid
(%)
Young fledging
of No. eggs
hatching (%)
Young fledging
of No. eggs
laid (%)
Apus apus^
(England)
74.011
74.5
59.0
Apus apus2
(Switzerland)

76.0
85.8
65.2
o
Apus melba
94.4
86.0
80.9
76.0
Apus caffer^
98.9
88.6
86.0
76.2
(Kenya)
Apus caffer-5
81.0
70.3
57.0
(South Africa)
Cypsiurus parvus^

54.2
31.5
17.1
Chaetura pelgica7

89.5
96.1
86.0
Chaetura brachyura8
95.0
51.7
53.5
26.7 K
Cypseloides rutilus^
93.1



Cypseloides rutilus8
84.3
65.8
68.4
36.1
Collocalia maxima^

29.2
65.4

Collocalia esculenta^

76.1
74.7

Collocalia salangana^

51.5
78.5

Lack and Lack, 1951. ^Weitnauer, 1947. ^Lack and Arn, 1947. ^Moreau, 1942a.
^Schmidt, 1965. ^Moreau, 1941. ^Fischer, 1958. 8This study. ^Snow, 1962. ^Medway, 1962a.
78.0 per cent when eggs ejected prior to start of incubation are omitted.
to
vo


62
Development of Horneothermy
Young swifts of both species essentially lack any
thermoregulatory capacity at hatching. When they are not
brooded their body temperature quickly drops to near ambient
temperature (Figs. 12-13). Body temperatures as low as 25-
27 C were recorded for C. rutilus; the lowest body temperature
recorded for C. brachyura nestlings was 31.9 C. The thermo
regulatory capacity of both species improves as they grow older,
and at the end of the third week of nestling life there is little
decline in body temperature even during extended periods without
brooding.
Nestlings tested in a cold chamber (Fig. 1) at approxi
mately 5 C showed rapid decreases in body temperature, as much
as 9.8 degrees within 5 minutes. A total of 101 tests were made
on 31 nestlings of C. brachyura and 72 tests on 12 C. rutilus.
The rate at which body temperature dropped lessened sharply with
increasing age (Fig.. 14). This lessening in temperature decline
represented an increase in the thermoregulatory capacity of the
nestlings through both an increased capacity for thermogenesis
and decreased heat loss. The decrease in body heat loss could
be due to the appearance of an insulating feather coat or a
decrease in the surface to volume ratio of the nestling. C.
rutilus seems to have an efficient coat of insulation early in
nestling life in the form of a down-like semiplume covering.
In addition, its contour plumage grows in very rapidly. C.
rutilus and C. brachyura, however, perfect their thermoregulatory


61
Behavior. The vocalizations of these nestling swifts
are quite limited. C. rutilus nestlings only make a very soft
twittering when disturbed and give no calls during feeding. By
comparison C. brachyura nestlings utter a prolonged loud rasping
rattle when disturbed and particularly during feeding. This
call starts and stops abruptly, and if one bird starts, its
nest-mates are quick to join in. This "disturbance" call
(Fischer, 1958) is restricted to the time of feeding and its
associated activity and excitement once the eyes are open.
Prior to this the slightest disturbance, whether an external
influence or merely the sudden activity of one member of the
brood, may trigger this call, which can be heard at some distance.
Neither of these swifts foul the nest during the nestling
period. Fecal wastes are carefully voided over the rim of the
nest by the young swifts. As noted by others this often results
in large accumulations of trash under the nests. Much of the
material found below swift nests, however, consists of the
chitinous remains of their insect food and does not appear to
have passed through the digestive tract. Legg (1956) found
insect remains around a nest of Cypseloides niger, part of which
appeared to be in the form of a pellet. Thus it seems probable
that swifts, like many other insectivorous birds, regurgitate
pellets made up of the indigestible chitinous portions of their
insect prey and that much of the material accumulated under their
nests, or in some cases in the nest (Rowley and Orr, 1965), comes
from these pellets.


GENERAL DESCRIPTION
Chaetura brachyura is one of four similar-appearing
congeneric species that occur in Trinidad. It is a small bird
about 115 mm long with a short stubby tail (28-33 mm) and long
narrow wings (117-127 mm). In fresh plumage it is dark black-
/
brown, except for the rump and under tail coverts which are
pale ashy brown. The throat is slightly paler than the breast.
The feathers of the darker areas, particularly the remiges,
have a noticeable greenish gloss or iridescence. In worn
plumage the gloss is purple or completely bleached out to a
lusterless dark brown, and the bird appears paler, particularly
on the throat, and is more brownish than black. Occasional
individuals have been collected in late summer with extremely
light brown underparts, but the cause of this is not understood.
Birds in juvenal plumage are less glossy on the body areas than
adults and have a more grayish tinge to the paler rump and under
tail areas.
Cypseloides rutilus appears to be a larger swift
(135 mm) owing to its longer tail (38-42 mm), but its wings are
about the same length (119-128 mm) as those of C. brachyura.
In over all color C. rutilus is dark sooty black-brown, darker
on the wings and tail than on the body. The males have a
complete collar of rufous feathers covering the nape, auricular,
8


50
Table 7. Daily weight (grams) and relative growth rate (per
cent) of Chaetura brachyura.
Days from
hatching
No.
Mean
weight
Range
Mean
weight
change
Per cent rela
tive growth
per day
0
20
1.6
1
0 -2.1/2
__
,
1
18
2.1
1
1/4-2.3/5
0.5
27.1
2
13
2.8
2
1/4-3 1/2
0.7
28.7
3
10
3.7
2
1/4-4 1/2
0.9
27.8
4
10
5.1
3
1/2-6 1/4
1.4
34.0
5
10
6.3
5
3/4-7 1/4
1.2
19.1
6
8
7.4
6
-9
1.1
16.0
7
9
8.7
4
-11
1.3
16.1
8
16
11.1
8
1/4-15
2.4
24.3
9
9
11.2
5
1/2-15
0.1
0.8
10
15
13.5
11
1/2-16 3/4
2.3
18.6
11
14
16.1
13
-19 1/2
2.6
17.6
12
14
16.2
13
1/2-19.
0.1
0.6
13
7
18.3
15
3/4-20
2.1
12.1
14
9
19.0
17
1/2-21 3/4
0.7
3.7
15
11
18.1
13
-22 1/4
-0.9
- 8.6
16
8
19.1
17
1/2-21 1/2
1.0
13.9
17
7
19.6
18
-22
0.5
2.5
18
6
22.2
17
3/4-22 1/2
2.6
12.4
19
7
20.2
17
1/2-23 3/4
-2.0
- 9.4
20
5
20.9
19
1/2-23
0.7
3.4
21
7
20.2
17
3/4-22 1/2
-0.7
- 3.4
22
6
19.0
17
1/4-22 1/2
-1.2
- 9.5
23
5
18.9
16
-21
-0.1
- 0.5
24
8
18.8
13
3/4-21 1/4
-0.1
- 0.5
25
11
19.7
16
-21
0.9
4.6
26
7
19.0
15
1/2-21 1/4
-0.7
- 3.6
27
7
19.4
17
1/2-23
0.4
2.0
28
6
18.0
17
-20
-1.4
- 7.4
29
6
18.7
17
1/4-21 3/4
0.7
3.9
30
6
18.4
16
1/4-20 1/4
-0.3
- 1.6
31
7
16.5
14
1/4-18 1/2
-1.9
-10.8
32
3
17.0
16
-18 1/2
0.5
2.9
33
5
16.6
15
-17 3/4
-0.4
- 2.3
34
4
15.7
14
1/4-17
-0.9
- 5.5
35
4
15.4
13
-17
-0.3
- 1.9
36
1
16.0
--
0.6
3.8
37
2
14.3
13
1/2-15
-1.7
-11.2
*


66
capacities at about the same rate and there is little difference
in their body weight, and hence surface to volume ratio, during
their first two weeks of life. Thus it would seem that C.
brachyura must depend upon increased heat production to counter
act the effects of cold environmental temperatures. As the en
vironmental temperatures of their nest sites are usually quite
warm, they are only rarely exposed to such cold conditions and
the need for increased thermogenesis.
Torpor
The insect food of swifts may be markedly affected by
varying weather conditions. In the temperate regions, where
acute food shortages lasting several days are of common occur
rence, both adult and nestling swifts routinely drop their body
temperatures at night and enter a state of torpor (Koskimies,
1950I Bartholomew, Howell, and Cade, 1957). The young of Apus
apus can fast as long as 9 days by utilizing their stored fat
deposits and decreasing their body temperature and metabolism
at night (Koskimies, 1950). Similar reactions have been observed
for several species of tropical swifts when deprived of food
for several days in captivity (Howell, 1961; pers. obser.).
Under natural conditions no healthy adult or nestling of either
C. brachyura or C. rutilus exhibited a body temperature below
the maximum that it was capable of maintaining, and none appeared
to be in less than a fully active, awake condition. On several
occasions nestlings which appeared to be injured or in an ex
tremely weakened condition had abnormally low body temperatures.


INTRODUCTION
Swifts of the family Apodidae form a well-defined group
of streamlined, fast-flying birds which spend most of the day
light hours on the wing in pursuit of their insect prey. They
occur throughout the world but are most abundant in tropical
regions. Although the biology of swifts has been studied in
Africa (Moreau, 1941, 1942a, 1942b), South America (Sick,
1948a, 1948b, 1959) and Malaysia (Medway, 1962a, 1962b), the
family as a whole is still poorly known. The nests of several
species have only recently been discovered (Rowley and Orr,
1962) and others are undescribed. A new species remained un
detected in a well studied part of northwestern South America
as late as 1962 (Eisenmann and Lehmann, 1962). The difficulty
of locating swift nests, which are usually solitary and often
in inaccessible cliff crevasses or in hollow trees, has clearly
hindered the study of additional species, particularly in the
tropics. At present, detailed life history data are confined
for the most part to a few species of the temperate zone (Lack
and Lack, 1951, 1952; Weitnauer, 1947; Fischer, 1958).
The island of Trinidad, having probably the largest
swift fauna for an area its size, offers abundant opportunities
for ecological studies. The preliminary work by Snow (1962) in
dicated the practicality of a detailed comparison of two of the
1


42
The ultimate factor governing departure of the fledglings
is probably the cessation of feeding by the adults. Young birds
quite capable of flying were observed to spend much or all of
the day roosting in the nest cavity, so long as the adults con
tinued to feed them. Several birds, which escaped while being
handled, successfully flew away and yet were found again roosting
on subsequent daytime visits. Snow (1962) also observed young
birds to "return to their nest hole by day after their first
flight." It is quite possible that young birds more than 30
days old, still found roosting by day, were making occasional
short flights before entirely abandoning the nest cavity. Two
35-day-old swifts, caught roosting in their nest cavity, were
fully capable of sustained flight at this age and successfully
returned when released at a point nine miles away. The earlier
observations by Snow (1962) indicated that "the young can fly
if disturbed as early as 28 days after hatching;if undisturbed,
they do not usually leave until they are 30-40 days old."
Cypseloides rutilus
In C. rutilus, as in all swifts except species of
Chaetura, there is no separation of the nestling and fledgling
periods as the young remain in the nest until the time they can
fly and feed themselves. This combined nestling-fledgling period
in C. rutilus is somewhat longer than in C. brachyura, being
closer to 40 days. All available figures exceed 35 days and most
fall between 37-43 days, averaging 39-30 days. These figures are
in agreement with those determined by Snow (1962). Young C.


BREEDING SEASONS
Most land birds in Trinidad have a well defined breeding
season. In contrast to the annual period of molt which shows
little yearly variation, the breeding season varies considerably
from species to species and from year to year (Snow and Snow,
1964). The breeding seasons for the two swifts C. brachyura
and C. rutilus extend from April until late August or early
September but vary within this period considerably from year
to year. The season coincides with the height of the annual
rainy period when insects are presumably most abundant, and
it probably represents an adaptive synchronization that assures
adequate food when young are to be fed. A similar adaptive
relationship seems to exist in Trinidad with the swallows,
which also depend upon flying insects for their food (Snow and
Snow, 1964).
Although the ultimate factor regulating the breeding
season seems to be an abundant food supply at the time of
nestling growth, the proximate environmental factors are more
obscure. The role of photoperiod as a proximate factor con
trolling breeding in tropical and equatorial birds is still
subject to debate. Experimental work has shown that the gonads
of several low-latitude birds respond to increasing photoperiods,
as has been amply shown for temperate latitude birds (Marshall
27


20
Fig. 4. Nests of Cypseloides rutilus; a) "Cone-shaped,"
b) "disk-shaped."


29
1962). In 1964 when there was an extremely wet winter and
spring, particularly in the more easterly parts of Trinidad,
the breeding activities of C. brachyura began very early,
although the main rainy season did not appear to start until
late May. A summary of the number of C. brachyura nests begun
in the years 1957 to 1964 in half-month intervals is presented
in Table 2. Several other Trinidadian birds appeared to be
directly influenced by the return of rainy weather. In several
cases the first strong rains of the season triggered repro
ductive activity. Almost immediately nest building and the
gathering of nest material was conspicuous and a peak in the
number of eggs laid soon followed (Snow and Snow, 1964).
Temporary dry spells also sharply reduced breeding in several
species.
C. rutilus started its breeding activities later than
C. brachyura and in most years showed a greater population
synchrony (Table 3). The first sign of their renewed nesting
was always the appearance of a fresh lining of greenery in the
old nests in preparation for their re-use. Prior to the start
of the rains this material is in short supply since much of it
dies away during the dry season and regains its previous lush
ness only when the rains return. It appears that C. rutilus
depends upon the reappearance of suitable nest material to
begin its breeding cycle. Such plant material is in turn de
pendent upon the return of the full summer rains and in some
cases the rising of water levels in the streams.


100
1962b. The swiftlets (Collocalia) of Niah Cave, Sarawak.
Part II, Ecology and regulation of breeding. Ibis,
104:228-245.
1962c. The relation between the reproductive cycle, moult,
and changes in the sublingual salivary glands of the
swiftlet Collocalia maxima Hume. Proc. Zool. Soc.
Lond., 138:305-315.
Meikeljohn, A. H.
1928. Swifts taking food from under eaves. Brit. Birds,
22:89.
Michael, Charles M.
1927. Black swift nesting in Yosemite National Park. Condor,
29 :89-98.
Michael, Enid
1933. A young black swift. Condor, 35:30.
Miller, Alden H.
1959. Response to experimental light increments by andean
sparrows from an equatorial area. Condor, 61:344-347.
Moreau, R. E.
1941. A contribution to the breeding biology of the palm
swift, Cypselus parvus. Journ. East Africa Uganda
Nat. Hist. Soc., 15:154-170.
1942a. The breeding biology of Micropus caffer streubelii
Hartlaub, the white-rumped swift. Ibis, 1942:27-49.
1942b. Colletoptera affinis at the nest. Ostrich, 13:137-147.
Orton, J.
1871. Notes on some birds in the museum of Vassar College.
Am. Nat., 4:713.
Parkes, Kenneth C., and George A. Clark, Jr.
1964. Additional records of avian egg teeth. Wilson Bull.,
76:147-153.


BODY TEMPERATURE
40-
o
0 38-
3 6-
34-
32-
1 1 1 1 r
6 8 10 12 14
AGE IN DAYS
~l r-
16 18
I I
20 22
Fig. 12. Body temperatures of nestlings of Chaetura brachyura when
unbrooded.- Vertical lines represent daily range in body temperatures,
curve connects daily means. Typical daily range in ambient temperature
26.0-30.5 C.
O'
w


25
poured a small waterfall, and just outside the spray zone of
the fall. Of the 15 nest sites observed during this study 2
were along mountain streams, 6 were in a river gorge, 4 in
sea caves, and 3 were in main-made culverts under a road or under
a bridge. Nine of these sites were found by Snow (1962).
The largest concentration of nests was in the rocky
walled "gucharo gorge" cut into limestone by the Arima River
near the head of Arima Valley. This gorge is located on the
Spring Hill Estate and has been a nesting place for these swifts
for at least 40 years, a nest being reported from there in 1926
(Belcher and Smooker, 1936). Individual nests were situated
along the gorge at varying intervals the least being about 35
feet. Elsewhere, the least distance I have recorded between
two active C. rutilus nests was about 7 feet. In this case
the two nests were on the walls of a cave-like rock archway
8 feet above a channel of water which cuts through Saut DEau
Island, an offshore islet on the north coast of Trinidad. It
is noteworthy that these swifts had to cross about a quarter
mile of ocean to reach the nearest feeding area. The swifts
inhabiting sea caves on Huevos Island probably also crossed
stretches of water in getting to mainland feeding area.
The most prominent organisms sharing these nest sites
were a variety of bats (mostly of the family Phyllostomidae)
which used the shady areas as daytime roosts. Several species
of small frogs and a cave cricket could be found in the vicinity
of the nest sites. On one occasion a small snake, Leptodeira



FOOD AND FEEDING HABITS
A poorly known aspect of swift biology is their feeding
habits. Although some information exists on the types of food
collected and the rate at which it is brought to the young,
there is only fragmentary information on where and at what rate
it is collected.
In Trinidad, particularly during clear, sunny weather,
mixed flocks of swifts are commonly seen moving up and down the
valleys of the northern range, overhead at one instant, several
miles away in a matter of minutes and back overhead shortly
thereafter. During the summer rainy season these birds are often
observed on the advancing edge of one of the intermittent
showers so abundant at that time of the year. The flocks may.
contain up to seven of the nine species of swifts recorded in
Trinidad. These are only temporary associations, and if the
birds are observed over longer periods certain specific feeding
patterns can be seen.
Chaetura brachyura is by far the most widely distributed
species in Trinidad and is observable at almost all elevations.
It is the only Chaetura that regularly forages over the savanna
areas and is decidedly more abundant there and over the lower
parts of the northern range than over areas above 1200 feet
elevation. One pair feeding young in a nest at an elevation of
500 feet in Arima Valley "used to fly off down the valley in the
70


FLEDGING SUCCESS
The mortality during the nestling and fledgling periods
for C. brachyura was approximately equal to that during incuba
tion (Table 6). Only 53.5 per cent of the 58 hatchlings suc
cessfully fledged, and only 26.7 per cent of the 112 eggs laid
resulted in fledged young. For C. rutilus the mortality rates
of eggs and nestlings were also about equal, with 68.4 per cent
of the 19 hatchlings successfully fledging, or only 36.1 per
cent of the total of 36 eggs laid.
As indicated by Snow (1962), the figures for C. brachyura
may not be typical of nests other than in man-made structures,
and there may well have been some additional mortality resulting
from the frequent visits and repeated handling which were part
of this study. There is, however, no information available for
any species of Chaetura in a natural nest site. The only
information on other Cypseloides swifts is for CL niger, which
had a similarly high rate of nest failures, particularly in the
nestling stage (Hunter and Baldwin, 1962).
The causes of egg and nestling losses are not clear.
At least one nestling of Cypseloides niger was seen to fall from
the nest (Knorr, 1961:168), and it is possible that many of the
losses of C. rutilus are similarly due to young birds accidentally
failin9 out of the nest. This is less likely in C. brachyura in
45


ADULT WEIGHT
The average adult weight of C. brachyura, based on a
sample of 240 individual weights, was 18.3 g with a range of
15 1/2-22 g. Snow (1962) reported an average weight of 19.8
g, but this value was influenced by the inclusion of a very
fat, non-breeding female weighing 30 grams, a weight 8 g
heavier than any other recorded for C. brachyura. This value
is however, within the expected weight range of the extremely
similar species Chaetura chapmani, to which perhaps it should
be attributed. The average weight of 24 juveniles of C.
brachyura, captured in roosting flocks of adults during Septem
ber and October 1964, was not appreciably different from that
of the adults although a few juvenile individuals ranged as
low as 14-15 grams, which is below the minimal weight recorded
for any adult.
The average adult weight of C. rutilus was 20.2 g and
ranged from 17 3/4-24 1/4 g in a sample of 45 individual weights.
There was a slight sexual dimorphism, males being heavier than
females. The weights of 24 males averaged 20.6 g and ranged
from 19 1/4-22 1/4 g while 19 females averaged 19.6 g with a
range of 17 3/4-24 1/4 grams. This difference is significant
(P<.02).
Monthly mean weights for both sexes of C. brachyura
68


General development 53
Feathers 53
Eyes 58
Bill and feet 58
Behavior 61
Development of horneothermy 62
Torpor 66
ADULT WEIGHT 68
FOOD AND FEEDING HABITS 70
FEEDING OF YOUNG 81
MOLT 84
PARASITES AND PREDATORS 85
DISCUSSION 87
SUMMARY 93
LITERATURE CITED 95
BIOGRAPHICAL SKETCH 103
IV


WING LENGTH IN MM
Fig. 9. Growth of the wing of Chaetura brachyura and Cypseloides rutilus.
Vertical lines represent ranges, curves connect daily means. Wing length
measured along chord from carpal joint to tip of longest primary.
Ui
in


99
1956b. Further notes on the breeding biology of the swift
Apus apus. Ibis, 98:606-619.
1956c. Swifts in a Tower. Methuen and Co., London. 239 pp.
Lack, David, and Hans Am
1947. Die Bedeutung der Gelegegresse beira Alpensegler.
Omith. Beob., 44:188-210.
Lack, David, and Elizabeth Lack
1951. The breeding biology of the swift, Apus apus. Ibis,
93:501-546.
1952. The breeding behaviour of the swift. Brit. Birds;
45:186-215.
Lack, D., and D. F. Owen
1955. The food of the swift. Journ. Animal Ecology. 24:
120-136.
Legg, Ken
1956. A sea-cave nest of the black swift. Condor, 58:183-187.
Maher, William J.
1964. Growth rate and development of endothermy in the snow
bunting (Plectrophenax nivalis) and lapland longspur
(Calcarius lapponicus) at Barrow, Alaska. Ecology,
45:520-528.
Marshall, A. J., and H. J. deS. Disney
1956. Fhotostimulation of an equatorial bird (Quelea quelea,
Linnaeus). Nature, 177:143-144.
Marshall, A. J., and S. J. Folley
1956. The origin of nest cement in edible-nest swiftlets
(Collocalia spp.). Proc. Zool. Soc. London, 126:383-
389.
Medway, Lord
1961. The identity of Collocalia fuciphaga (Thunburq). Ibis,
103:625-626.
1962a. The swiftlets (Collocalia) of Niah Cave, Sarawak.
Part I, Breeding biology. Ibis, 104:45-66.


37
represent an adaptive curtailment of the reproductive rate
favoring the greater survival of a lesser number of young.
Eggs were usually laid at the rate of one every other
day. On a few occasions disturbances of the nest or inclement
weather appeared to prolong the laying period. Five eggs in
a single clutch weighed 1, 1, 1, 1-1/4 and 1-1/2 grams.
Clutch size in C. rutilus is very small, as is true
of all species of Cypseloides. Of 25 clutches observed from
1962 to 1964, 23 were of 2 eggs and 2 of 1 egg. Of 32 clutches
observed by Snow only one case of a clutch of a single egg was
noticed and he attributed this to a bird breeding for the first
time.
The interval between the laying of the two eggs was
more irregular than for C. brachyura. The second egg of the
clutch was usually laid two days after the first, but intervals
of as long as five days occurred during which the first egg was
left uncovered in the nest. The eggs from two clutches weighed
2-1/4, 2-3/4, 2-3/4 grams. Extraparental cooperation was not
observed in this species.


NESTS AND NEST SITES
Chaetura brachyura
There are relatively few records for nests in natural
settings for most species of Chaetura. The available informa
tion indicates that all tend to utilize hollow trees or stumps
and occasionally affix their bracket-shaped nests to vertical
rocky ledges or the walls of caves (Lack, 1956a). Most species
in the genus have been quick to accept various artificial
equivalents of these natural hollows, and as early as the 1870s
accounts began to appear in journals of their nesting in
numerous man-made structures including chimneys, wells, cis
terns, and a variety of buildings (Lack, 1956a; Fischer, 1958)#
The species most clearly illustrating this habit is the North
American chimney swift, Chaetura pelgica (Linnaeus), which
"now breeds much more often in chimneys than in trees" (Lack,
1956a). Other New World species of Chaetura known to use man
made structures are C. vauxi vauxi (Townsend) in temperate
areas (Baldwin and Hunter, 1963; Baldwin and Zaczkowski, 1963)
and C. vauxi aphanes Wetmore and Phelps, Jr. (Sutton, 1948),
C. andrei Berlepsch and Hartert (Sick, 1959) and C. brachyura
(Haverschmidt, 1958) in tropical South America. In Trinidad
C. brachyura has previously been reported to use chimney and
sea-cave nest sites (Belcher and Smooker, 1936), as well as
11


4
the northern half of Arima Valley, but a few were in sea
caves on the north coast, particularly near the town of
Blanchisseuse.


* BHPHHgnHjB r-v
FEEDING OF YOUNG
The feeding of the nestlings was seen on several occasions
but never close enough to be sure of details. Presumably it is
similar to that reported for other swifts in that the adult
carries the food to the nest in the mouth or throat. The adult
inserts its bill into the mouth of the nestling and passes the
food to it. As brought to the nest, the food items are often
glued together with saliva forming a compact wad or "food ball."
Very young birds generally receive only part of a ball of food,
the rest being shared with other nestlings or retained by the
adult. When older, a single nestling usually receives the entire
food ball.
The rate of feeding of C. brachyura is similar to that of
other species of Chaetura for which there is information. The
intervals between visits of adults to the nest range from 2.5-
45 minutes and average 20.5 minutes.
Like other swifts of the genus, Cypseloides rutilus is
characteristically absent from the nest for extended periods of
time particularly after brooding had ended. The feeding inter
vals of C. rutilus are irregular and lengthy. The one interval
for which an exact time was obtained was 36 minutes. All other
intervals recorded were in excess of 100 minutes, although the
exact duration was not determined.
81


34
Table 4. Distribution of clutch sizes of Chaetura brachyura
by half-month intervals for years 1962 to 1964.
Clutch Size
Totals
Period 1
2
3
4
5
6
7
16-30 April
1
1
2
1 -15 May
1
2
2
5
16-31 May
1
1
3
1
6
1 -15 June
1
1
16-30 June
2
1
1
4
1 -15 July
2
1
1
4
16-31 July
1
1
2
1 -15 Aug.
1
1
16-31 Aug.
1
1
All months 0
3
8
8
5
1
1
26


15
Fig
3
Nests of Chaetura brachyura


CLUTCH SIZE
Like other species of Chaetura, C. brachyura lays
large clutches. The 26 complete clutches observed from 1962
to 1964 ranged from 2-7 eggs, with a mean clutch size of 3.8
(Table 4). This is 'slightly less than for the other Chaetura
species that have been studied (Table 5). In the earlier
observations on this same population from 1957 to 1961, 41
clutches ranged in size from 1-6 and had a mean of 3.6 eggs
per clutch (Snow, 1962; Table 2). Unusual clutches of 8 and
9 have been recorded for C. pelgica and C. brachyura, re
spectively, but in each case they appeared to result from two
females laying in the same nest (Fischer, 1958; Snow, 1962).
The 7-egg clutches recorded for C. vauxi (Baldwin and Zaczkowski,
1963) and C. brachyura (this study) both seemed to be the product
of a single female. In both of these cases the eggs were laid
or hatched within a short time of each other.
An additional example of two females laying in a single
nest was noted for C. brachyura in 1963. In this case a clutch
of 4 eggs was laid in a newly constructed nest between 7-13 May
at the usual rate of 1 egg every other day. Incubation began
on 14 or 15 May, and the clutch still consisted of only 4 eggs
on 17 May. On 21 May, however, a fifth egg was noticed and
when the nest was checked on 23 May a sixth had been added.
33


18
nestling which fell out of the nest.
Cypseloides rutilus
The nests of four of the ten species presently included
in the genus Cypseloides are still unknown. There is, however,
a good deal of similarity in both site and nest material among
those that have been described. Lack, in his review of the
nesting habits of swifts (1956a), states that "all the species
of Cypseloides for which the nest is reliably known agree in
building on steep cliffs, usually in association with water,
making a cone-shaped nest of mud and moss lined with fern-
tips or twigs." For Cypseloides niger (Gmelin), Knorr (1962)
has delimited five "ecological requirements" for nest sites:
"the presence of water, high relief inaccessibility
for terrestrial marauders, darkness, and lack of flyway obstruc
tions in the vicinity of the nest." This type of nesting
situation is so characteristic that numerous nests of C. niger
have been successfully found by searching for these "ecological
requirements" rather than birds showing indications of possible
breeding (Michael, 1927; Knorr, 1961, 1962). The same pro
cedure was used in this study to find additional C. rutilus
nest sites in Trinidad and, I am sure, could be applied with
equal success to locating the yet undescribed nests of C.
biscutatus (Sclater), C. cherriei Ridgway, C. cryptus Zimmer,
and C. lemosi Eisenmann and Lehmann. Only two nests attributed
to Cypseloides are not in agreement with this general pattern
or the descriptions of other nests of the same species. They
represent one nest each of C. fumigatus (Streubel) (Holt, 1927-


WT. IN GRAMS
Fig. 7. Growth curve of Chaetura brachyura. Semi-log plot, vertical lines
represent range of daily weights, curve connects daily means.
00


40
nest sites. The higher hatching success of C. rutilus, compared
to C. brachyura, is probably similarly based on the fact that C.
rutilus nests overhang water on smooth surfaces or inaccessible
ledges, and are less often disturbed by predators than the nests
of C. brachyura in manholes or hollow trees. Several of the
"inaccessible" sites recorded for other species were in man-made
structures and may not, therefore, reflect mortality rates when
under natural conditions.


ACKNOWLEDGMENTS
I extend ray deep appreciation to Pierce Brodkorb for
his valuable supervision of this problem. Sincere thanks are
%
also due to the other biologists who critically read the manu
script: E. G. Franz Sauer, Thomas J. Walker, Brian K. McNab,
and Frank G. Nordlie. I am particularly grateful to David W.
Snow for acquainting me with these swifts and their nest sites
and for making his notes available to me. Miss Jocelyn Crane
and the Department of Tropical Research of the New York Zoologi
cal Society greatly facilitated my field work in Trinidad.
Thanks are also due Mrs. H. Newcomb Wright, Spring Hill Estate,
Arima Valley, Trinidad, for her hospitality and permission to
study the swifts nesting there. I wish to gratefully acknowledge
the financial support for this study received from the Frank
M. Chapman Memorial Fund of the American Museum of Natural
History in 1962 and 1963, and in 1964 the National Science
Foundation (Summer Fellowship for Graduate Teaching Assistants)
and Cyril K. Collins.
To John Beckner who identified the nest materials, and
to John F. Anderson, Frank M. Mead, Thomas E. Snyder, Phyllis
T. Johnson, and Robert E. Woodruff, who identified the arthropods,
I am also grateful.
XX


35
Table 5. Clutch size of swift species in the genus Chaetura.
Species
Number
of
clutches
Range
Average
clutch
size
Reference
C. pelgica
25
2-5
4.2
Fischer, 1958
T
27
3-7
4.0
Dexter (in Fischer, 1958)
t!
19
4-6
5.3
Sherman, 1952
C. brachyura
41
H
O'
3.6
Snow, 1962
It
26
2-7
3.8
this study
C. andrei
3
4-5
4.6
Sick, 1959
C. vauxi
?
3-7
?
Baldwin & Zaczkowski,
1963; Bent, 1940.
J


13
Fig. 2. Manhole nest sites of Chaetura brachyura, Waller Field,
Trinidad.


INCUBATION
The incubation period was calculated from the laying of
the last egg to the hatching of the last young. For C. brachyura
the 17-18 day period determined by Snow (1962) was confirmed,
except in one case, when the period was only 16 days. A period
of 48-72 hours usually elapsed between the hatching out of the
first and last young.
The incubation period for all clutches of C. rutilus
agreed with the 22-23 day period determined by Snow (1962).
The siblings in the broods of two usually hatched within 24
hours of each other.
Although substantial losses often occurred during the
incubation period, there was a high percentage of hatching
among those eggs of both species which reached the expected
date of hatching (Table 6). The figure recorded in this study
for C. rutilus (84.3 per cent) is lower than that of Snow (93.1
per cent) because of the desertion of a clutch and it may have
resulted from the greater frequency of disturbing visits. Thus
the higher value may be more characteristic of undisturbed
nests. The hatching rate, based on the total number of eggs,
is quite low for both species as compared with similar values
for other swifts (Table 6). Those species showing a high
hatching success are also those with the more inaccessible
38


14
water or had water flowing through the bottom drainage pipe
during the nesting season. In three sites nests were destroyed,
and in one case an adult was trapped by rising water in the
hole. Although the nest sites were usually brightly illuminated
there was very little circulation of air, and the relative
humidity was in excess of 95 per cent at all times. The
temperature in these manholes had a range of from 25.0 to 33.3 C
during the nesting season. A characteristic daily range was
from a low of 26.0 to a high of 30.5 C.
Although nest building was not observed for this species,
the finished nest of C. brachyura is so similar to that of all
other New World species in the genus that the building process
must also be highly similar. The best studied species, C.
pelgica, collects nesting material by grasping tree-top
twig s in its feet and breaking them off while in flight
(Fischer, 1958). The nest is made entirely of such twigs
glued together and affixed to a vertical surface by means of a
secretion of the sublingual salivary glands. C. brachyura
shows a pronounced enlargement of these glands during the
breeding season, as has been reported for C. pelgica (Johnston,
1958) and several species of Collocalia (Medway, 1962c).
The nest of C. brachyura is a shallow half-saucer of
twigs which are 20-75 mm long and usually only 1-2 mm in di
ameter (Fig. 3). It is slightly smaller than the nests de
scribed for other species of Chaetura (Table 1). The nests were
glued to the walls of the manholes at varying heights, some
being near the top where they were in deep shadow and others


PARASITES AND PREDATORS
Ectoparasites in the form of mites (Acaria) and
feather lice (Mallophaga) were collected from both species.
Mallophagans were particularly abundant on nestlings during the
period when their feathers were first emerging from the sheath.
Mallophagan eggs were most abundant on the dorsal feathering of
the head and neck. Mites were noticed only on the feathers of
the wings, particularly on the vanes of the outer primaries.
Although these collections have not yet been identified, the
*
mallophagan species Dennyus brevicapitis has been reported from
C. brachyura in Trinidad, and Dennyus brunneitorques and Bureum
yepezi from C. rutilus in other parts of its range (Carriker,
1954, 1958).
One specimen of a flea, Polygenis dunni, was caught on a
young nestling of C. brachyura. This species has previously
been collected from several rodents in Trinidad and northern
South America (Johnson, 1957).
The only endoparasites observed were tapeworms (Taenia
sp.) collected from the intestines of both swifts.
Adult mortality in swifts is generally lower than in
smaller and slower-flying species of passerines (Lack, 1954).
No predators of adult swifts were observed during this study.
In Venezuela, Beebe (1950) noted a pair of nesting bat falcons
85


WT. IN GRAMS
+
I Ji'iiiiii 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34
AGE IN DAYS
Fig. 8. Growth curve of Cypseloides rutilus. Semi-log plot, vertical lines
represent range of daily weights, curve connects daily means.
I|r
36
vo


46
light of the strength of their feet and their ability to hold
tenaciously to the nest, even at very early ages.
No predation of eggs or nestlings has been observed for
either species. Two nestlings of C. brachyura and one of C.
rutilus were found that had been badly chewed by some animal.
As these nests were inaccessible to terrestrial predators it is
possible that this was the result of an attack by a bat of one
of the several species which commonly roosted in close proximity
to the swift nests. Other losses of both nestlings and eggs
might also be attributed to bat predation. Skutch (1964)
similarly suspected bats to be responsible for the disappearance
of eggs and nestlings from the inaccessible nests and the wounding
of a nestling of a hermit hummingbird. Some egg losses were also
probably due to accidental ejection from the nest by the adults,
as has been observed for other species (Lack and Lack, 1951;
Moreau, 1942a).


BOOY TEMPERATURE #C
0.2 4 6 8 10 12 14 16 18 20 22
AGE IN DAYS
Fig. 13. Bod;/ temperatures of nestlings of Cypseloides rutilus
when unbrooded. Vertical lines represent daily range in body
temperatures, curve connects daily means. Typical daily range
in ambient temperature 21.0-25.0 C.
o
-P-


RANGE
Chaetura brachyura inhabits the southernmost Lesser
Antilles and northern South America, with a single report in
southern Panama. It is abundant on the islands of St. Vincent,
Trinidad, and Tobago and on the mainland from Venezuela and
Colombia south to Peru and the Matto Grosso of Brazil.
Cypseloides rutilus ranges continuously from southern
Mexico to Peru and Bolivia and east through northern Venezuela
and Trinidad. A separate population also exists in the high
lands of southeastern Venezuela and the neighboring parts of
British Guiana.
10


69
varied between a low of 17.1 g (Oct. 1964) and a high of 18.7 g
(Aug. 1964). Daily means somewhat higher (18.9, 19.0 g) were
also recorded during August 1964. Eighteen individuals weighed
on two or three separate occasions, varied from as little as
1/4 g to as much as 2 1/2 g between successive weighings.
Monthly mean weights of C. rutilus varied from a low of 19.6
g to a high of 20.7 g, while daily sample averages varied from
19.0 to 21.1 g, both in October 1964. Eight individuals weighed
on two to four separate occasions varied as little as 1/4 g and
as much as 2 1/2 g between weighings.
Weight variations of these magnitudes are explainable
in terms of temporal variations in food availability. Similar
weight changes were recorded for Apus apus in England (Gladwin
and Nau, 1964) with sharp decreases in body weight being corre
lated with prolonged cold or rainy weather. Such weather greatly
decreases the aerial food supply of these swifts (Lack and Owen,
1955). There was no marked seasonal change in weight between
April and November in either C. brachyura or C. rutilus as is
typical of migrant swifts, particularly C. pelgica in temperate
North America (Coffey, 1958).


90
conditions (Lack and Lack, 1951; Lack and Am, 1947; Perrins,
1964; Moreau, 1941, 1942a, 1942b). There seems to be no reason
to doubt that other swifts in both temperate and tropical parts
of the New World are similarly food limited and have their
clutch size regulated by the same factors.
As shown in this study, clutch size of C. brachyura
resembles that of other species of Chaetura and is nearly double
the clutch size of Cypseloides rutilus. It would thus seem that
in Trinidad C. rutilus is capable of obtaining enough food to
nourish only two young, while C. brachyura can gather nearly
double that amount. As noted earlier only a partial overlap of
the feeding range of these swifts occurs with C. rutilus feeding
at higher elevations and also at higher altitudes. Even so, it
is hard to accept the view that the food decreases in abundance
by nearly 50 per cent with such shifts in feeding ecology and
hence is entirely responsible for the reduction of clutch size in
C. rutilus. It is equally hard to accept that C. rutilus is only
half as efficient at food gathering as C. brachyura. As noted
earlier, however, C. rutilus broods the young more continuously
and for a longer time than C. brachyura in order to contend with
the cold environment of its nest site. At such times C. rutilus
reduces the food supply available to its young by reason of the
restriction of foraging to but one adult at a time. The absolute
abundance of food may be the same or only slightly diminished in
its foraging range, but the effective food supply available to
the nestlings is much less. The combination of such reduction
in effective food supply, mainly through reduced foraging capacity,


51
Table 8. Daily weight (grams) and relative growth rate (per
cent) of Cypseloides rutilus.
Days from
hatching
No.
Mean
weight
Range
Mean
weight
change
Per cent rela'
tive growth
per day
0
7
2.1
2
-2 :
1/2
1
10
2.5
2
-3
0.4
17.4
2
7
3.5
2
3/4-4 1/2
1.0
33.6
3
10
3.9
3
1/4 -5
0.4
10.8
4
8
5.0
4
1/4 -6 :
1/4
1.1
24.8
5
13
6.3
5
1/2 -7 .
3/4
1.3
23.1
6
7
7.3
6
1/2 -8 :
3/4
1.0
14.7
7
7
10.6
8
-14
1/2
3.3
38.2
8
4
9.8
8
1/2 -12
1/4
-0.8
- 8.7
9
10
11.6
8
-13
1.8
16.8
10
3
12.8
9
3/4 -14
1/4
1.2
9.8
11
7
14.1
11
1/2-16
1.3
9.6
12
6
15.8
14
-18
1/2
1.7
11.3
13
6
16.6
14
1/2-17
3/4
0.8
4.9
14
4
18.2
17
-19
3/4
1.6
9.2
15
1
20.5
--
2.3
11.9
16
6
20.7
18
1/2-21
1/2
0.2
0.9
17
1
19.3

-1.4
- 7.0
18
6
21.0
20
-22
1.7
8.4
19
4
21.2
18
-26
3/4
0.2
9.3
20
4
23.9
21
1/2-24
3/4
2.7
11.9
21
6
22.5
18
1/2-26
-1.4
6.0
22
2
20.8
20
1/4-21
1/4
-1.7
- 7.8
23
3
25.5
25
-27
1/2
4.7
20.3
24
1
23.0

-2.5
-10.3
25
3
25.2
24
3/4-25
3/4
2.2
9.1
D
27
3
24.2
24
-25
-1.0
- 4.0
28
1
24.0

-0.2
- 0.8
29
3
26.2
23
1/4-28
3/4
2.2
8.7
30
4
23.6
22
1/2-26
1/4
-2.6
-10.4
Jl
32
1
20.3

-3.3
-15.0
34
3
24.4
23
326
1/2
4.1
18.3
35
1
24.0

-0.4
- 1.6
36
2
23.9
22
1/2-25
1/4
-0.1
- 0.4
37
1
24.3

0.4
1.6


30
Table 2. Distribution of Chaetura brachyura nests in half-
month intervals.
Period
1957*
1958*
1959*
1960*
1961*
1962
1963
1964
All
Years
1 -15
April
1
1
2
16-30
April
1
1
3
2
7
1 -15
May
5
4
1
3
1
2
4
4
24
16-31
May
4
3
2
3
2
1
2
4
21
1 -15
June
1
4
3
4
2
14
16-30
June
1
1
5
1
2
4
1
15
1 -15
July
3
2
1
3
3
1
13
16-31
July
1
4
2
1
1
1
**
1
11
1 -15
Aug.
3
1
2
3
1
**
1
11
16-31
Aug.
3
1
**
4
1 -15
Sept.
1
1
1
**
3
Total
19
16
16
14
21
13
12
14
125
*Data from Snow (1962)
**No observations


97
Eisenmann, Eugene
1961. Favorite foods of neotropical birds: flying termites
and Cecropia catkins. Auk, 78:636-638.
Eisenmann, Eugene, and F. Carlos Lehmann
1962. A new species of swift of the genus Cypseloides from
Columbia. Am. Mus. Novitates 2117:1-16.
Fischer, Richard B.
1958. The breeding biology of the chimney swift, Chaetura
pelgica (Linnaeus). N. Y. State Mus. and Sci. Serv.,
Bull., 368:1-141.
Gilbert, M. V.
1944. Swifts scavenging in house-martin's nests. Brit.
Birds, 28:135.
Gladwin, T. W., and B. S. Nau
1964. A study of swift weights. Brit. Birds, 58:344-356.
Gibb, John
1954. The breeding biology of the great and blue titmice.
Ibis, 92:507-539.
Haverschmidt, F.
1958. Schornsteine als Massenschlafplatz von Chaetura brachyura
in Surinam. Journ. f. Ornith., 99:89-91.
Holmes, Richard T.
1966. Breeding ecology and annual cycle adaptations of the
red-backed sandpiper (Calidris alpina) in northern
Alaska. Condor, 68:3-46.
Holt, E. G.
1928. An ornithological survey of the Serr do Itatiaya,
Brazil. Bull. Am. Mus. Nat. Hist., 57:251-326.
(reference from Lack, 1956)
Howell, Thomas R.
1961. An early reference to torpidity in a tropical swift
Condor, 63:505.


88
The pattern of nestling growth in both species is
typical of altricial birds, although greatly prolonged as com
pared to the several small passerines reviewed by Maher (1964).
Snow (1962) suggests that the inaccessibility of the nest has
caused a relaxation of selection for the accelerated growth of
nestlings so typical of most passerine birds nesting in the open.
Chaetura brachyura shows a pronounced similarity in all
aspects of its biology to all other New World species of Chaetura
that have been studied. In nest form, clutch size, nestling
growth pattern, feeding habits, and general behavior only minor
specific differences exist. For the most part these result from
the timing of events during development rather than being major
departures from the common pattern. This general similarity is
shown by an array of species which inhabit the area from temperate
North America south to subequatorial South America, and also
includes both sedentary and migratory species.
An equal degree of similarity exists between Cypseloides
rutilus and other congeneric species, although the little informa
tion available relates mainly to C. nlger.
Although both species studied show similarities to various
congeners, several pronounced intergeneric differences occur in
their reproductive activities. The nest site of C. rutilus is
colder and darker than that of C. brachyura. It is also less
accessible to predators and there are reduced losses of both
eggs and nestlings of C. rutilus. At the same time this environ
ment imposes several demands upon these swifts as a part of the
young. The newly hatched young swift has a very poorly developed


82
The best studied species of Cypseloides, C. niger, may
leave the nest at dawn and not return to feed the nestling until
nearly dusk (Smith, 1928). Some feedings have been observed in
the morning hours and indicate higher feeding rates at some
times, possibly when the nestling is very young. Occasionally,
an adult of this species has been observed to feed the nestling,
brood it, and then regurgitate a second meal for the young swift
several hours after the initial feeding (Michael, 1927). Two
adults collected at night at their roosts still had large amounts
of food in their throats, which would have enabled them to feed
the nestling a second time (Collins, unpubl.).
The most complete information is that for Apus affinis
in Kenya (Moreau, 1942b). This swift fed the young birds at
intervals ranging from less than 8 to 254 minutes but averaged
one feeding trip every 118 minutes for a brood of two. Broods
of one were fed at a slower rate and broods of three at a
significantly faster rate than either the broods of one or two.
Despite acceleration of feeding rate with increased brood size,
the rate per individual nestling decreased in larger broods.
In many species a flurry of feeding activity begins
shortly before evening roosting, with the adults making many
trips to the nest in a short period of time. Both Fischer
(1958) and Sherman (1952), however, found that C. pelgica
brought smaller quantities of food per trip during such visits,
occasionally only a single insect.
An increase in rate of feeding with increasing age of
the nestlings is indicated in some swifts (Kendeigh, 1952i97-98).


57
as also noted for C. brachyura. The tail reaches its full
length about the time the young fledges (Fig. 9), but the wing
does not complete its growth until early in the post-fledging
period (Fig. 10).
The major difference in the plumage development of
Chaetura and Cypseloides species is the appearance in the latter
group of a dark gray, down-like covering early in nestling life,
prior to the appearance of the regular contour feathers. Al
though referred to as natal down by earlier observers it has
been shown to consist of a loose-webbed semiplume type of
feather and forms part of the first teleoptile plumage (Collins,
1963). These feathers appear as subcutaneous dots as early as
the first day of nestling life. They may break through the skin
as early as 5-6 days after hatching although usually somewhat
later. They routinely emerge earlier than the previous estimate
of 8-9 days after hatching (Collins, 1963). These semiplumes
are freed of their sheaths for more than half of their length
shortly after they erupt from the skin, and thus the nestling
soon takes on a downy appearance (Collins, 1963; Fig. 3). The
semiplumes seem to reach their full length of about 13-14 mm
by day 19 and are entirely freed of their sheaths by day 26.
They are covered by the emerging contour plumage at about 28
days after hatching. Semiplumes are longest on the back and
rump and shorter on the head and underparts. They are found on
the margins of the pterylae, particularly on the dorsal aspect
of the body. Although semiplumes are generally absent from
the wings, there are occasionally a few along the lateral
/


59
the first weeks of nestling life. Both egg teeth are generally
unobservable by day 14, although a slight roughness on the culmen
sometimes can be detected on slightly older birds.
Grasping with the feet was noticed on the first day after
hatching in both species. The legs of C. brachyura seem to be
particularly well developed even very early in life and are
capable of supporting the nestling on a vertical surface within
48 hours after hatching. The feet of C. rutilus cannot support
a nestling in a similar fashion until about day 14. Michael
(1933) similarly noticed that Cypseloides niger had "the dainty
feet and slender legs of a songbird" and not the stronger limbs
characteristic of the white-throated swift, Aeronautes saxatilis
(Woodhouse). In their study of Chaetura vauxi, Baldwin and
Hunter (1963) also comment upon the particularly sharp claws
and strong toes as compared to Cypseloides niger. As was also
found in this study, Baldwin and Hunter (1963) note that the
young of Chaetura held on to the twigs of the nest so tenaciously
that a loss of claws was likely to result if care were not taken
in removing them from the nest. The strong feet of Chaetura
are an obvious adaptation enabling them to raise a larger brood
in their small nests. The ability to hold tightly to the nest
reduces the chances of one of a large brood being accidentally
jostled out of the nest, particularly during defecation. When
the nestlings are older and the nest becomes overcrowded (Fig.
11a) their strong feet enable them to climb out and support
themselves on the wall nearby until actual fledging (Fig. lib).


9
loral and malar regions, but not the interramal areas nor the
throat and upper portion of the breast. The females are
generally uniform dark brown. A few birds have a partial
rufous collar on the nape and extending laterally to the edges
of the throat, with sometimes additional flecks on the throat
and breast. Two such birds were collected and both proved to
be females. Despite numerous statements to the contrary it
is not the juveniles that completely lack the collar. In
fact, birds in juvenal plumage invariably have some rufous
present as a partial collar. The edges of the collar are not
so sharply delimited as in the adults, and the crown feathers
also have narrow reddish edges. The extent of the rufous
coloring in the juvenal plumage is variable, but it is never
so extensive as in adult males nor is it completely lacking
as in most adult females.


102
1964. Life histories of hermit hummingbirds. Auk., 81:5-25.
Smith, Emily
1928. Black swifts nest behind a waterfall. Condor, 30:
136-138.
Snow, David W.
1962. Notes on the biology of Trinidad swifts. Zoolgica,
47:129-139.
Snow, David W., and Barbara K. Snow
1963.
Breeding and the annual cycle in three Trinidad
thrushes. Wilson Bull., 75:27-41.
1964.
Breeding seasons and annual cycles of Trinidad
land-birds. Zoolgica, 49:1-39.
Sutton, George M.
1948.
Breeding of Richmonds swift in Venezuela. Wilson
Bull., 60:189-190.
Todd, W.
E., and M. A. Carriker, Jr.
1922.
The birds of the Santa Marta region of Colombia: A
study in altitudinal distribution. Ann. Carnegie Mus.,
14:1-611.
Tordoff, Harrison B., and William R. Dawson
1965.
The influence of daylength on reproductive timing in
the red crossbill. Condor, 67:416-422.
Udvardy,
Miklos D. F.
1954.
Summer movements of black swifts in relation to weather
conditions. Condor, 56:261-267.
Weitnauer, Emil
1947. Am Neste des Mauerseglers, Apus apus apus (L.)
Ornith. Beob., 44:133-182.


52
Table 9. Average daily growth rate (grams) and relative growth
rate (per cent) for five-day intervals for Cypseloides rutilus
and Chaetura brachyura.
Age
C. brachyura
Mean daily Mean daily
weight relative
change growth rate
C. rutilus
Mean daily Mean daily
weight relative
change growth rate
0-4
0.9
29.4
0.7
21.7
5-9
1.2
15.3
1.3
16.8
10-14
1.6
10.5
1.3
9.0
15-19
0.2
2.5
0.6
4.7
20-24
-0.3
-2.1
0.4
1.6
25-29
-0.02
-0.1
0.8
3.3
30-34
-0.6
-3.5
-0.4
-2.3


94
a down-like semiplume portion of its 'first teleoptile plumage
emerges at an early age and aids in thermoregulation.
The young of C. brachyura leave the nest when about 3
weeks old and hang on the walls of the nest cavity until fledging
at the age of 4-5 weeks. C. rutilus young remain in the nest un
til fledging at an age of 5-6 weeks.
These two swifts appear to feed on the same types and
sizes of aerial food. Their foraging ranges, however, only
partially overlap. C. rutilus feeds at higher elevations than
C. brachyura and to some extent also at higher altitudes. The
differences in foraging ranges may be an adaptation enabling them
to avoid interspecific competition for food. Similar adapta
tions seem to be present in other species of swifts.
. Most of the differences in the biology of these two
species of swifts are associated with reproduction and represent
adaptations of C. rutilus to the cool, damp environment of the
nest site.


71
direction of the savanna three miles away. They would return
from the same direction" (Snow, 1962).
Cypseloides rutilus was less often observed in flight and
then only in the upper part of Arima Valley or over the higher
parts of the northern range. Even though it nests in caves at
sea level on the north coast and at elevations of 500-1100 feet
in Arima Valley, it seems to forage exclusively over the forest
at higher elevations. Although the feeding ranges of the two
species overlap at the lower elevations around 500 feet, C.
rutilus is also comidonly observed at higher elevations including
the summit of El Tuchuche (3,068 feet), whereas C. brachyura
is uncommon above 1200 feet. Conversely, I have never observed
C. rutilus over the savanna areas where C. brachyura is abundant.
In addition to feeding at higher elevations, C. rutilus and
another swift, Panyptila cayennensis (Gmelin), appear at all
elevations to feed at greater distances above the ground than
most species of Chaetura. This habit was also observed for C.
rutilus in Trinidad (Snow, 1962) and for C. niger in Washington
(Rathbun, 1925). As this characteristic of feeding at higher
altitudes was most commonly noted during fine weather and
particularly when both C. rutilus and cayennensis were part
of mixed flocks containing one or more species of Chaetura, it
may be less characteristic of their day to day feeding activities
when not in association with other species.
In England, Apus apus generally feeds in the immediate
vicinity of the nests (Lack and Owen, 1955), whereas Cypseloides
niger makes daily trips of several miles from mountain nesting


75
Table 10. Contents of food balls collected from nestlings of
Chaetura brachyura and Cypseloides rutilus.
Food item
Number of
samples in which
it occurred
Number of
individuals
A.
Araneae
Chaetura brachyura
2
94
Lycosidae
1
1
Tetragnathidae
1
1
Linyphiidae
1
1
Clubionidae
1
12
Mi c ryph an ti dae
1 '
2
Oxyopidae
1
2
Thomisidae
1
16
Salticidae
1
34
Theridiidae
1
1
Araneidae
1
3
unidentified
1
21
Coleptera
6
73
Curculionidae
3
14
Apion sp.
1
1
Ceutorhynchus sp.
1
12
unidentified
1
1
Scolytidae
3
9
Cocotrypes sp.
2
7
unidentified
2
2
Cryptophagidae
1
2
Chrysomelidae
3
13
Lema sp.
1
3
Chaetocnema sp.
1
2
Systena sp.
2
2
Altica sp.
1
2
unidentified
1
4
Platypodidae
3
28
Platypus sp.
3
28
Staphylinidae
2
3
Coccinellidae
1
1
Nitidulidae
3
3
Stelidota sp.
1
1
Garpophilus sp.
2
2
Orthoptera
1
1
Hemiptera
2
10
Saldidae
1
1
Tingidae
1
9


12
subterranean manholes and a nest box erected for swifts (Snow,
1962).
The C. brachyura nest sites followed in this study were
all in vertical manholes which were part of the underground
drainage system of Waller Field (Fig. 2). Eleven of these
sites were discovered by Snow and kept under observation by him
from May 1957 until September 1961 (Snow, 1962). An additional
ten holes used as nest or roosting sites were found during this
study and observed during 1962-1964. For the most part the
manholes were cylindrical concrete tubes from 4-20 feet deep,
connecting with a smaller lateral drainage pipe at the bottom.
The holes had an inside diameter of about 4-1/2 feet, and
usually had a concrete top pierced by a circular access hole, 2
feet in diameter, which at one time had been closed by a metal
manhole cover. One hole, slightly narrower and made of bricks,
had an uneven surface as opposed to the smooth walls of those
made of concrete. The only site not in one of these holes was
located in a subterranean, concrete-walled room about 20 feet
long, 10 feet wide, and 10 feet high. The swifts entered
and left this room through a 12-inch square opening in the
ceiling, which was flush with the ground level. The tops of
several of the manholes were also flush with the ground;
others protruded as much as 4 feet above ground. One of the
manholes used predominantly as a roosting site was nearly
roofed over with a metal sheet covered by cement, with only a
very small hole, 5-1/2 by 10 inches, providing access for the
swifts. Fourteen of the 21 sites were partially filled with


78
of each size food item is shown in Fig. 13. As was true for
the prey species diversity, C. brachyura appears to feed on a
wider range of prey items than C. rutilus. Again it seems likely
that this seeming difference is an artifact of the sampling. If
only the similar food items (winged ants and termites) of the
two swift species are compared (Fig. 15), the interspecific dif
ferences in the size of prey selected are not significant.
Winged ants and termites appear in the food samples throughout
the breeding season, and the absence of any difference in size
of these food items selected by the swifts may indicate a similar
absence of difference in size of other food items selected. If
so, C. rutilus and C. brachyura would appear to select similar
kinds and sizes of food items, although their foraging ranges
J
only partially overlap.
In England, Apus apus usually takes food items ranging
in size from 2-10 mm, rarely larger or smaller. Within this
range it tends to take larger items from 5-8 mm long during fine
weather when insects are abundant. During rainy or cold weather
there are fewer insects available of all sizes, and the swift
includes more of the smaller prey items from 2-5 mm in its diet
(Lack and Owen, 1955).
From this it seems that larger species, such as Apus
apus, may occasionally select food items larger than any taken
by either C. brachyura or C. rutilus and rarely take prey as
small as some regularly taken by these smaller swifts. Similarly,
276 food items collected by another large swift, Cypseloides
niger, in Veracruz, Mexico, ranged from 2-12 mm in length, with


LIST OF TABLES
Table Page
1. Nest dimensions of swifts of the genus Chaetura. 16
2. Distribution of Chaetura brachyura nests in half
month intervals. 30
3. Distribution of Cypseloides rutilus nests in half
month intervals 31
4. Distribution of clutch sizes of Chaetura brachyura
by half-month intervals for years 1962 to 1964 34
5. Clutch size of swift species in the genus Chaetura 35
6. Average hatching and fledging success of swift
species 39
7. Daily weight (grams) and relative growth rate
(per cent) of Chaetura brachyura 50
8. Daily weight (grams) and relative growth rate
(per cent) of Cypseloides rutilus 51
9. Average daily growth rate (grams) and relative
growth rate (per cent) for five-day intervals for
Chaetura brachyura and Cypseloides rutilus .... 52
10.Contents of food balls collected from nestlings
of Chaetura brachyura and Cypseloides rutilus. 75
v


16
Table 1. Nest dimensions of swifts of the genus Chaetura.
(W) width of nest at greatest point along rim, (FB) greatest
distance from back to front rim, (D) greatest depth from rim
to bottom of nest. Measurements in centimeters.
Number
of
nests
Average
Range
C. brachyura
W
6.2
5.4 6.9
FB
8
5.3
4.0 6.5
D
2.5
1.8 3.3
C. pelgica-1-
W
--
7.5 -11.3
FB
?

5.0 7.5
D

2.5 3.1
C. vauxi2
W
10.0

FB
1
6.0

D
4.0
-
C. andrei3
W
8.5
7.5 9.5
FB
3
4.3
3.5 5.0
D
3.7
2.5 3.0
C. chapmani^
W
6.9
FB
1
5.9

D
2.4

-'-Fischer, 1958; Bendire, 1895
2Dickinson, 1951
3Sick, 1959
^Collins, unpub.


21
the nest, then, seems to be entirely dependent on whether it
is affixed to a smooth rocky surface or perched on a narrow
ledge. Larger species such as C. zonaris, require greater
support for their nests and consequently would be expected to
build on ledges when available. The smaller and lighter weight
species such as C. rutilus and C. fumigatus, could also build
cone-shaped nests fixed to vertical surfaces. Presumably owing
to its extreme weight (170-180 g), the largest New World swift,
Cypseloides semicollaris (Saussure), builds no nest at all and
lays its eggs on sandy ledges in caves (Rowley and Orr, 1962).
Regardless of the shape, C. rutilus nests appeared to
be primarily of soft plant material with some mud intermixed.
This mud presumably helped hold the nest material together and
attach it to the rock as no salivary glue appeared to be used.
The universal use of saliva in swift nest construction has
already been questioned (Marshall and Folley, 1956; Johnston,
1961), and its use should not be assumed for C. rutilus until
further information is available. The plant materials used in
Trinidadian C^_ rutilus nests included a liverwort of the genus
Plagiochilax, the lycopsids Selaginella cladorrhizans and cf.
arthritica, and the filmy fern Trichomanes membranaceum. All of
these plants grow in damp shady places, particularly on rocky
outcrops along streams (Fig. 5) and thus in proximity to the
nest sites of these swifts. There is no information available
on the collection of the nest material or nest construction by
any species of Cypseloides. Nests are used during several
successive years, and a new lining of fresh green material is


32
This sequence of events was particularly noticeable
in 1964. In that year the easterly parts of Trinidad experi
enced a very wet winter and spring. As mentioned (p 29), this
unseasonable wet weather stimulated very early breeding by C.
brachyura in that area. At the same time Arima Valley had a
fairly normal dry season which did not end until 22-23 May.
These two days were marked by nearly'continuous heavy rains.
Prior to this time there had been no indication of breeding
that year at any known C. rutilus nest site in the valley.
The stream water levels were low and suitable nest material
was unavailable. Several days after these first heavy rains
the mossy stream-side plant life had recovered a great measure
of its former lushness. On 29 May six C. rutilus nest sites
were checked and all six nests were relined with fresh greenery.
On 3 June three of these contained one or more eggs. By 6 June
four of the six nests had full clutches while a fifth contained
a partial clutch. The remaining nest, although relined, was not
used that year.


26
annulata, was caught on a ledge only a few feet from an active
swift nest. As its name implies, the "gucharo gorge" also
contained a small colony of the gucharo or oilbird, Steatornis
caripensis, as did two of the sea caves in which C. rutilus was
thought to nest (Snow, 1962).
Environmental temperatures at typical C. rutilus nest
sites ranged from 18.8-26.2 C, but h'ad a characteristic daily
range of 21.5-25.0 C. Sea cave nest sites tended to be a bit
warmer, with maximum temperatures reaching 27.2 C. The range
in temperature recorded over 13 months at one nest site in the
river gorge was 18.8-23.8 C. Relative humidity at the nest
sites was always in excess of 95 per cent.


72
areas to lowland feeding areas in Washington (Rathburn, 1925).
During the breeding season both species also make long-range
movements of several hundred miles to avoid prolonged adverse
weather conditions (Lack, 1955; Udvardy, 1954). Chaetura pelgica
in New York was seen foraging over a field about 1/4 mile from
the nest and regularly brought in Ephemeroptera, presumably
collected over a stream 1/8 mile away. Itoo color-marked birds
were also seen foraging 2 3/4 and 4 miles, respectively, from
their nests (Fischer, 1958).
Weather-influenced differences in the height of feeding
have been noticed for Apus apus and C. niger, which feed higher
in the air on sunny days and low over the ground or water during
rainy or cloudy weather (Lack and Owen, 1955; Rathbun, 1925).
Day to day variations in feeding habits have been noticed
for many species of swifts as they exploit temporary abundances
in their air-born insect prey. They do not merely fly through
the air, mouths open, catching only whatever happens to get
scooped up. If closely observed, swifts can be seen to change
their flight direction to snap up an attractive prey item.
Confirmation of this is provided by the comparison of food
samples with random samples of aero-plankton. The swift-
gathered samples are clearly richer in the larger species
which are less characteristic of true aero-plankton (Lack, and
Owen, 1955).
The foraging habits of C. brachyura and C. rutilus did
not change noticeably from day to day although the swifts often
descended to nearly ground level during wet weather to feed on


98
Hunter, William F., and Paul H. Baldwin
1962. Nesting of the black swift in Montana. Wilson Bull.
74:409-416.
Johnson, Phyllis T.
1957. A classification of Siphonaptera of South America
with descriptions of new species. Mem. Ent. Soc.
Wash., 5:1-298.
Johnston, David W.
1958. Sex and age characters and salivary glands of the
chimney swift. Condor, 60:73-84.
1961 Salivary glands in the black swift. Condor, 63:338.
Kahl, M. Philip, Jr.
1962. Bioenergetics of growth in nestling wood storks.
Condor, 64:169-183.
Kendeigh, S. Charles
1952. Parental care and its evolution in birds. Illinois
Biol. Monographs, 22:1-356.
Knorr, Owen A.
1961. The geographical and ecological distribution of the
black swift in Colorado. Wilson Bull., 73:155-170.
1962. Black swift breeds in Utah. Condor, 64:79.
Koskimies, Jukka
1950. The life of the swift, Micropus apus (L.), in relation
to the weather. Ann. Acad. Sci. Fenn., 15:1-151.
Lack, David
1954. The Natural Regulation of Animal Numbers. Clarendon
Press., Oxford. 343 pp.
1955. The summer movements of swifts in England. Bird
Study, 2:32-40.
1956a. A review of the genera and nesting habits of swifts.
Auk, 73:1-32.


19
1928) and C. zonaris (Shaw) (Todd and Carriker, 1922). In
both cases the nests were described as being made of twigs
glued together with saliva. The nest of the former also con
tained five young and was located inside a house gable, an
%
improbable site and brood size for a species of Cypseloides.
Ihese nests are quite obviously more correctly referred to some
species of Chaetura.
In the first description of the nest of C. rutilus,
Orton (1871) states it to be "chiefly of moss, very compact,
and shallow, and located in dark culverts about two feet above
the water." Belcher and Smooker (1936) characterize nests
in Trinidad as "half cups stuck to a perpendicular wall of
rock over a swiftly running stream." Snow (1962)
describes the nest as "a substantial bracket, semicircular
in horizontal section with a wide depression for the eggs .
[and]. made of various plant fibers, usually including
some moss."
My observations indicate some variation in the shape
of C. rutilus nests. Some nests, built on smooth vertical
surfaces, in fact resembled truncated cones similar to those
of C. fumigatus and C. zonaris (Reboratti, 1918). Others,
located on small rock ledges, were little more than pads of
nesting material, somewhat thicker along the outer rim, with
a wide but shallow cup for the eggs (Fig. 4). This type of
nest closely resembles the "disk-shaped" ones reported for C.
zonaris and _C. niger when similarly located on damp rocky
ledges (Rowley and Orr, 1965; Michael, 1927). The shape of


74
method, used earlier by Lack and Owen (1955), did not injure the
the birds if done carefully and was not repeated frequently
enough to disrupt the pattern of normal growth.
The contents of these samples were extremely varied
(Table 10). Eight were homogeneous masses of either winged
ants or winged termites. Heterogeneous samples varied from one
or two types of insects to a mixture of some forty species
representing six orders of insects and nine families of spiders.
The samples varied in size from a nearly complete food ball of
326 insects to only a few remnants of a meal. Since it was not
always possible to get complete food balls from the young birds,
no comparison was made between the number or weight of food items
brought in different trips. In four cases it was possible to get
food samples from two C. brachyura nestlings of a single brood
on a single visit to the nest. In each case both nestlings had
received similar food. In the one case where samples were ob
tained on the same day from C. brachyura nestlings of different
broods in nest sites about a mile apart, one nestling had re
ceived a homogeneous sample of winged ants while two nestlings
at the other site had both received mixed samples of Diptera,
Coleptera, and Hymenoptera. Day to day variation in the food
brought in by a single pair of adults was extensive and usually
included both homogeneous and heterogeneous samples. No analysis
of seasonal differences in food items was possible since these
samples could only be collected while there were young birds in
the nest.
Interspecific differences in the type of food collected


89
capacity for temperature regulation, which improves slowly
during the first weeks of nestling life. If left unbrooded in
the cold environment of the nest, C. rutilus nestlings would
rapidly lose heat to the environment, and much of the energy
available for growth would be expended in wasteful thermogenesis.
To prevent such energy-draining heat loss, the adults brood the
nestlings until their capacity for thermoregulation has reached
a stage where the amount of heat lost without brooding will no
longer appreciably slow further growth and development. In C.
rutilus and other congeners the development of thermoregulation
is aided by the early appearance of an insulating feather coat.
This insulation includes the normal contour feathers, which
break out of the sheath at an early date, as well as a down-like
semiplume portion of the first teleoptile plumage, which also
grows in rapidly. Thus the intergeneric differences in nest
ling development and adult behavior represent adaptations that
enable CL rutilus and other species of Cypseloides to contend
with the cold environment of the nest site.
The regulation of clutch size in birds has been studied
in diverse taxa in many parts of the world. The most complete
information is based on studies of temperate passerine species in
which the clutch size "has been adapted by natural selection to
correspond with the largest number of young for which the parents
can, on the average, provide enough food" (Lack, 1954:31).
Studies on Old World temperate and tropical swifts have shown
these birds to be similarly food limited with their clutch size
adapted to the number of young which can be raised under average


BIOGRAPHICAL SKETCH
Charles Thompson Collins was bom on March 9, 1938,
at Long Branch, New Jersey. In June 1956 he was graduated
from the Pingry School, in Elizabeth, New Jersey. He received
the degree of Bachelor of Arts from Amherst College in June
1960, and the Master of Science degree from The University of
Michigan in June 1962. Since then he has worked toward the
degree of Doctor of Philosophy at the University of Florida.
He is a member of the Society of the Sigma Xi, Ameri
can Ornithologists' Union, Cooper Ornithological Society,
Wilson Ornithological Club, and Urner Ornithological Club.
103


58
margin of the humeral tract and a short row of them in the
apterium between the lesser secondary coverts and the marginal
coverts (Collins, 1965). A similar down-like plumage has been
recorded for other Cypseloides species (Hunter and Baldwin,
1962; Orr, in litt.) and probably occurs in all members of the
genus. The semiplume covering and the early emergence of the
contour feathers from their sheaths are aids to thermoregulation
in nestlings living in a cooler microclimate.
Eyes. The two species have a noticeable difference in
the opening of the eyes. Those of C. brachyura are partially
open on day 16 and completely open on day 18. This is slightly
later than has been observed for other species of Chaetura
(Fischer, 1958; Baldwin and Zaczkowski, 1963). In C. rutilus
they open gradually with an interval of more than a week between
the first partial opening and complete opening of the eyes. In
this species the young may have partially opened eyes as early
as day 7, but usually this first occurs on day 8-9. Their
eyes are not fully open until about 16-17 days after hatching.
Bill and feet. The newly hatched swifts of both species
are pale flesh pink except for the bill and claws which have a
slight gray pigmentation at the tip, especially apparent in C.
brachyura. The lining of the mouth is also a flesh pink. In
both species a prominent egg tooth is present on the upper man
dible (similar structures were reported in other genera by
Parkes and Clark, 1964), and a hardened whitish cap occurs on
the lower mandible. The egg teeth gradually disappear during


54
to break through the skin, usually doing so around day 4-5.
The rectrices are somewhat slower, emerging on about day 6-7,
followed by the contour plumage when the birds are about 8 days
old. The feathers of the dorsal tract grow somewhat faster
than those of the cervical, capital, and ventral tracts and begin
to emerge from their sheaths about 15-16 days after the young
hatch. Emergence in the remaining tracts is somewhat later.
The flight feathers begin to break out of their sheaths 12-13
days after hatching. The growth of the wing is shown in Fig. 9
and the tail in Fig. 10. The tail completes its growth about
26-27 days after hatching, but the wing does not reach full
length until shortly after fledging.
C. rutilus acquires its feather covering in a sequence
generally similar to that of C. brachyura but it differs
slightly in timing. The remiges first break through the skin
on about day 5, and the rectrices about 9 days after hatching.
The contour plumage first appears as dark subcutaneous streaks and
emerges through the skin about 10-11 days after hatching. The
flight feathers begin to emerge from their sheaths about 13-14
days after hatching, about one day later than noted for C.
brachyura. The contour feathers, however, begin to break through
their sheaths much earlier in C. rutilus despite their having
emerged through the skin somewhat later than in C. brachyura.
These feathers begin to erupt 13 days after hatching as opposed
to day 15-16 for C. brachyura. The contour feathers of C.
rutilus on the cervical, capital, and ventral tracts are some
what slower in their development than those of the dorsal tract,


DISCUSSION
In their general biology Chaetura brachyura and
Cypseloides rutilus appear similar to most swifts for which
information is available. They are almost exclusively aerial
in their activities and feed on air-borne arthropods, mostly
insects.
The breeding season of both swifts coincides with the
abundance of aerial food associated with the summer rainy season.
Many other species of Trinidadian birds have similarly altered
their reproductive cycles so that breeding occurs at a time of
maximal abundance of suitable food. For the swallows, as for
the swifts, the peak in breeding and the maximal abundance of
food both occur early in the rainy season. For the nectar
feeding hummingbirds and the bananaquit (Coereba flaveola), how
ever, the maximal food abundance and the peak in breeding occurs
at the height of the dry season (December-May) at the time when
many forest trees and vines are in flower (Snow and Snow, 1964).
The absence of a pronounced peak in food abundance may result in
an extended breeding season as in two" species of thrushes (Snow
and Snow, 1963). Beyond the tropics, a similar adaptive rela
tionship often exists between breeding season and maximal food
abundance, as in temperate zone tits of the genus Parus and
arctic sandpipers of the genus Calidris (Gibb, 1954; Holmes,
1966).
87


METHODS AND MATERIALS
During the nesting season individual nests were checked
regularly, usually once a day or less in order to avoid exces
sive disturbance and possible desertion.
In 1962 adults and nestlings were marked with numbered,
colored plastic bands and, starting in 1963, also with U. S.
Fish and Wildlife Service numbered, aluminum bands. Nestlings
less than 8-10 days old could not be banded and were marked
with spots of color applied with a felt marking pen to the
skin of the back or belly. Color marking of nestlings and
adults was only used to a limited extent. An attempt to color
mark a prebreeding flock of C. brachyura, by painting the pri
maries of one wing yellow, proved unsuccessful as the birds
could not be readily distinguished in the field.
Weights of adults and nestlings were obtained with
spring balance of the type obtainable from the British Trust
for Ornithology. This balance was calibrated in half-gram
intervals, and weights were estimated to the nearest quarter
gram.
Environmental temperatures were obtained by means of
Sixs type maximum-minimum recording thermometers. Body
temperatures were measured with a small bulb mercury ther
mometer made by the Schultheis Corporation. Readings were
5