BULLETIN
OF THE

FLORIDA STATE MUSEUM

BIOLOGICAL SCIENCES

Volume 11 Number 5

THE COMPARATIVE BIOLOGY OF TWO SPECIES
OF SWIFTS IN TRINIDAD, WEST INDIES

Charles T. Collins

:tu of..

UNIVERSITY OF FLORIDA
Gainesville

1968



Numbers 6/4he:BULEETIN·.OF THE FLORIDA SufATTE MU~EfiM am pu>
lisbed at irregular intervals. yolumes contain about] 800 pages and, are not
necessarily completed in any ofie:dale*dar year.

WALTER AUFFENBERG, Managing Editor

OLIVER L. AUSTIN, JR., Editor

Consultants for this issue:

PAUL H. BALDWIN

ALLAN R. PHILLIPS

Communications concerning purcha56 6r exchange of the publication and all
manuscripts should be· addressed to the Managing Edit6r of the Bulletin, Florida
State Museum, Seagle Building, Gainesville, Florida: 82601.

Published Februafy 2,„1968 Price for this issue $.90



THE COMPARATIVE BIOLOGY

OF TWO SPECIES OF SWIFTS

IN TRINIDAD, WEST INDIES.

CHARLES T. COLLINSl

SYNopms: The comparative biology of the short-tailed swift, Chaetura bracht/ura,
and the chestnut-collared swift, Cypseloides Tutilus, was studied in Trinidad dur-
ing parts of 1962-66. In many aspects both species proved similar to congeners
for which information exists. Both breed during the rainy season when insect
food is abundant, but their breeding activities are triggered by different·proximate
factors.

Ch. brachgura lays a clutch averaging 8.8 eggs in nests of twigs cemented to
the walls of manholes. Cyp. rutilus lays a clutch of 2 eggs in nests of mosses,
lycopsids, and ferns built on rocky outcrops over rivers and mountain streams,
and occasionally in sea caves. The environmental temperature of nest sites of
rutitus is lower than for those of brachvura. and the nestlings of rutilus are
brooded longer and more continuously than nestlings of brachyum. C!/p· rutlus
has a lower mortality of eggs and young than brachvura, its nest sites being
presumably less accessible to predators.

The young of brachgura grcjw more rapidly than those of mtilus, but both
species perfect their capacity for thermoregulation at about the same rate. In
rutilus, a down-like semiplume portion of its first teleoptile plumage emerges at an
early age and aids in thermoregulation. The young of brach,ura leave the nest
when about 3 weeks old and hang on the walls of the nest cavity until they
fledge at the age of 4-5 weeks; rutilus young remain in the nest until they Redge
at 5-6 weeks.

These two swifts appear to feed on the same types and sizes of aerial food,
but their foraging ranges only partially overlap; rutilus feeds at higher elevations
than brachyura and to some extent at higher altitudes. The differences in forag-
ing ranges may enable 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 swift are asso-
ciated with reproduction and reflect adaptations by rutilus to the cool, damp en-
vironment of the nest site.

i The author, Chapman Research Fellow, Department of Ornithology, American
Museum of Natural History, New York, completed this work while a graduate
student at the University of Florida. Gainesville. An earlier version formed his
doctoral dissertation and was accepted by the Graduate School in Tune 1966.
Present address: Department of Biology, Fairleigh Dickinson University, Madi-
son, New Tersey. Manuscript submitted 14 April 1967.-ED.

Collins, Charles T. 1968. The Comparative Biology of Two Species of Swifts in
Trinidad, West Indies, Bull. Florida State Mus., vol. 11, no. 5, pp  257-820.



258 BULLETIN FLORIDA STATE MUSEUM Vol. 11

TABLE OF CONTENTS

INTRODUCTION 258
ACKNOWLEDGMENTS 259
STUDY AREA 260
METHODS AND MATERIALS 260
GENERAL DESCRIPTION 263

Range 264
NESTS AND NEST SITES 264

Nests of the Genus Chaetura 264
Nests of the Genus Cypseloides 269

BREEDING SEASONS 276
CLUTCH SIZE 279
INCUBATION AND HATCHING SUCCESS 281
PARENTAL CARE 283

Chaetura brachyura 283
Cypseloides rutilus 284
Other Species 284

BROODING 284
FLEDGING SUCCESS 285
GROWTH 286

Body Weight 286
General Development 290
Development of Homeothermy 295
Torpor 297

ADULT- WEIGHT 298
FOOD AND FEEDING HABITS 299

Feeding of Young 805
ADULT BEHAVIOR 807
MOLT 810
PARASITES AND PREDATORS 810
DISCUSSION 311
LITERATURE CITED 814

INTRODUCHON

Swifts of the family Apodidae form a well-defined group of stream-
lined, fast-fiying 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 plentiful 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 sev-
eral species have only recently been discovered ( Rowley and Orr,
1962; Collins, 1968) and others are undescribed. A new species re-
mained undetected in a well studied part of northwestern South



1967 COLLINS: SWIFTS OF TRINIDAD 259

America as late as 1962 ( Eisenmann and Lehmann, 1962). The diffi-
culty of locating swift nests, which are usually solitary and often in
inaccessible cliff crevices or in hollow trees, has clearly hindered the
study of many species, particularly in the tropics. Currently detailed
life history data are limited for the, most part to a few species of the
temperate zone ( Am-Willi, 1960; Lack and Lack, 1951, 1952; Weit-
nauer, 1947; Fischer, 1958).

The island of Trinidad, with one of the largest swift faunas for
an area its size in the world, offers abundant opportunities for ecolog-
ical studies. The preliminary work by Snow ( 1962) indicated the
practicality of a detailed comparison of two of the nine species of
Trinidadian swifts. These two species, the Short-tailed Swift, Chae-
tura brachyum ( Jardine), and the Chestnut-collared Swift, Cypse-
Zoides rutilus ( Vieillot), are approximately the same size but have
striking differences in nesting ecology, clutch size, and the develop-
ment of the young. The present study was undertaken to analyze
these differences and, where possible, to point out their adaptive
significance.

Differences in nest type have been shown to be useful in differen-
tiating species of swiftlets of the genus Collocalia ( Sims, 1961; Med-
way, 1961, 1966; Brandt, 1966), while differences in ecology and
clutch size appear to be significant indicators of higher intrafamilial
relationships ( Lack, 1956). Thus the study of the comparative ecol-
ogy of additional species, in conjunction with studies of the anatomy,
osteology, and paleontology of swifts, should provide knowledge use-
ful in understanding the evolution of the Apodidae.

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. MeNab, Frank G. Nordlie, and Eugene
Eisenmann. I am particularly grateful to David W. Snow for ac-
quainting me with these swifts and their nest sites and for making
his notes available to me. Jocelyn Crane Griffin and the Department
of Tropical Research of the New York Zoological Society greatly fa-
cilitated 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



260 BULLETIN FLORIDA STATE MUSEUM Vol. 11

gratefully to acknowledge the financial support for this study received
from the Frank M. Chapman Memorial Fund of the American Mu-
seum of Natural History in 1962, 1963, and 1966, and in 1964 from
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.

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 at an elevation of 800
feet four miles north of the town of Arima, 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 twelve months of field work in Trinidad dur-
ing part or all of the breeding seasons of 1962-1964, exact dates being
26 June - 1 September 1962; 25 April - 11 July 1963; 8 May - 11
November 1964; 19 October - 6 November, and 24 November - 1
December 1966.

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 mon-
tane rain forest at elevations of 2500 to 3000 feet, and the rocky coast-
line of the north shore of the island. The principal nesting area for
Ch. brachyura was Waller Field, a United States Air Force base
deserted for more than ten years and heavily overgrown with grasses,
brush, and low second-growth forest ( Fig. 1.) except for the roads
and a few cement structures. Most nests of C!/P. Tutilus were located
in 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

Individual nests were checked regularly during the nesting season,
usually not more often than once a day in order to avoid excessive
disturbance and possible desertion.



1967 COLLINS: SWIFTS OF TRINIDAD 261

In 1962 adults and nestlings were banded with numbered bands
of colored plastic and, starting in 1963, also with U. S. Fish and Wild-
life Service numbered njetal 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 mark-
ing of nestlings and adults was only used to a limited extent. An
attempt to color mark a prebreeding flock of Ch. brachyura by paint-
ing the primaries of one wing yellow proved unsuccessful, as the
birds could not be readily distinguished in the field. Adults and nest-
lings were weighed with a 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 taken with Six's type maximum-
minimum recording thermometers. Body temperatures were meas-
ured with a small bulb mercury thermometer made by the Schultheis
Corporation. Readings were taken with the bulb inserted about 10
mm into the cloaca.

Cold stress experiments were a part of the investigation of nestling

1 -*if

-* 1 . I

Figure 1.-Savanna area near manhole nest sites of Chaetura brachyum, Waller
Field, Trinidad.



262 BULLETIN FLORIDA STAT'E MUSEUM Vol. 11

Figure 2.-Cold chamber used in tests of thermoregulatory capacity of nestling
swifts.

thermoregulation. These required a 6xSx5-inch cold chamber made
of foam plastic insulation material 11/k" thick ( Fig. 2.), which four
6-oz. cans of "Skotch Ice" ( refreezable liquid) kept at a temperature
of approximately 5°C for several hours. Nestlings were placed in-
dividually in the chamber in the field 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, the tests caused no apparent ill effects.

Swifts of both species were captured at night roosting places for
weight and molt studies. Flocks of Ch. brach!/ura were generally
confined in a roost site und examined the following morning. A hand
net was used to capture Cup. rutilus adults roosting at night in a river
gorge in Arima Valley; they were held in captivity over night and
released the following morning. Although mist nets were successfully
employed in Trinidad in catching large numbers of swifts of several
other species ( Collins, 1967a) only a few individuals of brach!/ura
and none of rutilus were mist-netted in this study.



1967 COLLINS: SWIFTS OF TRINIDAD 268

GENERAL DESCRIPTION

Chaetura brachyural 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 slight-
ly 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 collected in
late summer have extremely light brown underparts, the cause of
which is not understood. Birds in juvenal plumage have less gloss on
the body than adults and show a more grayish tinge on the paler
rump and under tail areas.

Cypseloides rutilusl 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 Chaetura brachgura and, as shown later,
the body weights of the two species are similar. In over all color
rutilus is dark sooty black-brown, darker on the wings and tail than
on the body. The males havi a complete collar of rufous feathers
covering the nape, auricular, loral, and malar regions, and the throat
and upper portion of the breast, but not the interramal area. 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 collected in Trinidad both proved to be females. Despite
numerous statements to the contrary, juveniles do not completely lack
the collar, but 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 varies, but it is never
so extensive as in adult males nor is it completely lacking as in most
adult females.

Albinistic feathers were observed in the adult plumages of both
brachgura and rutilus. In brachyura albinism was confined to just a
------

1 In Trinidad, Ch.  brach!/ura is represented by the race brachyum and Cup.
rutilus by the race futilus ( Peters, 1940). Although Peters ( 1946) places rutilus
in the genus Chaetura, I concur with the presently accepted views of Zimmer
( 1958) and Lack ( 1956) that the species is more properly included in the genus
Cypseloides.



264 BULLETIN FLORIDA STATE MUSEUM Vol 11

few feathers on the upper breast or head, while in rutilus it sometimes
involved numerous feathers on several parts of the body ( Collins,
1967b).

RANGE
Chaetura brachgura inhabits the southernmost Lesser Antilles and

northern South America. It occurs on the islands of St. Vincent, Trini-
dad, and Tobago and on the mainland from Venezuela and Colombia
south to Peru and the Matto Grosso of Brazil.

Cypseloides rutilus ranges from southern Mexico to Peru and
Bolivia and east through northern Venezuela and Trinidad. A sep-
arate population also occupies the highlands of southeastern Vene-
zuela and neighboring Guyana.

NESTS AND NEST SITES

NESTS OF THE GENUS Chaetura

Relatively few records for nests in natural settings exist for most
species of Chaetura, and for those of some species we have no knowl-
edge at all. The available information suggests that all tend to utilize
hollow trees or stumps and may 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 ac-
counts began to appear in journals of their nesting in such man-made
structures as 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 man-made structures are uauxi vauxi ( Townsend) in
temperate areas ( Baldwin and Hunter, 1963; Baldwin and Zaczkow-
ski, 1963) and vauxi aphanes Wetmore and Phelps, Jr. ( Sutton, 1948),
andrei Berlepsch and Hartert ( Sick, 1959), and brachyura ( Haver-
schmidt, 1958) in tropical South America. In Trinidad brach{/ura
has previously been reported to nest in chimneys and sea-caves
( Belcher and Smooker, 1936), as well as in subterr:mean manholes
and a nest box erected for swifts ( Snow, 1962).

Chaetura brachyura-The nest sites of brachyura followed in this
study were in vertical manholes that were part of the underground
drainage system of Waller Field ( Fig. 3). Snow ( 1962 ) discovered



1967 COLLINS: SWIFTS OF TRINIDAD 265

11 of these sites and kept them under observation from May 1957
until September 1961. I found an additional 10 holes used as nest or
roosting sites during this study between 1962 and 1964. Most of the
manholes were cylindrical concrete tubes 4 to 20 feet deep and con-
nected with smaller lateral drainage pipes at the bottom. Their inside
diameter was about 41/2 feet, and their concrete tops were usually
pierced by a circular access hole 2 feet in diameter, which was at
one time closed by a metal manhole cover. One hole, slightly nar-
rower and made of bricks, had a more uneven surface than 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
nearly flush with the. ground level ( Collins, 1967c). The tops of
several of the manholes were flush with the ground; others protruded
as much as 4 feet above it. 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, 51,4 by 10 inches, for the
swifts to enter. Fourteen of the 21 sites were partly Blled with water
or had water flowing through the bottom drainage pipe during the
nesting season. Water rising in the hole destroyed the nests in three
sites and trapped one adult. Although the nest sites were usually
brightly illuminated they had very little air circulation, and the relative
humidity was always above 95 per cent. The temperature in these
manholes during the nesting season ranged from 25.0 to 33.3°C. 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 fin-
ished nest of brachyum is so similar to all those reported for other
New World species in the genus that the building process must be
quite similar. The best studied species, Chaetura pelagica, collects
nesting material by grasping treetop 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. Ch. brachyura
shows a pronounced enlargement of these glands during the breeding
season, as has been reported for pelagica (Johnston, 1958) and sev-
eral species of Collocalia ( Marshall and Folley, 1956; Medway,
1962c).

The nest of brachyura is a shallow half-saucer made of twigs 20-75
mm long and usually only 1-2 mm in diameter ( Fig. 4). It is slightly



266 BULLETIN FLORIDA STATE MUSEUM Vol. 11

WEEdliki/.C/~I<Avilfir//#JiFFF/A# Demiem
~~~~~~~~;'~'7f  --®~~ f>-~ ir i -~41'U'' r <4, fi '*~
9,1, 'S.,f,t*.#fN...11 .

~6*<e~;4'' i#~69'i'Fi~JI.~0&=~~4
1*419 7**i;r ,

/6 4

-e#ze.*j»41**51,94.NiA*1,6

Figure 8.-Manhole nest sites of Chaetura brachvura, Waller Field, Trinidad.



1967 COLLINS: SWIFTS OF TRINIDAD 267

smaller than the nests described for some other species of Chaetura
( Table 1). The nests were glued to the walls of the manholes at
varying heights, some being near the top under the overhang where
they were in deep shadow and others 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 most of them fell off the
wall soon after the nesting season. Before re-use additional twigs ap-
peared to be added to the nest, as has been recorded for Ch. pelagica
( Amadon, 1936; Fischer, 1958). In only a few cases did brachyura
build up the semicircular arch of saliva on the wall above the nest so

TABLE 1. NEST DIMENSIONS OF SWIFTS OF THE GENUS Chaetura. (W)-

width of nest at greatest p6int 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. brach!/ura
6.18 5.4- 6.9

FB 8 5.88 4.0 - 6.5
D 2.52 1.8- 8.8

C. pelagical
W 7.5 - 11.8
FB ? 5.0 - 7.5
D 2.5 - 8.1

C. vauxi2
W 10.0
FB 1 6.0
D 4.0

C. andreis
8.5 7.5 - 9.5

FB 8 4.8 8.5 - 5.0
D 8.7 2.5- 3.0

C. chapmani4
6.9

FB 1 5.9
D 2.4

1Fischer, 1958; Benlire, 1895
?Dickinson, 1951
BSick, 1959
4Collins, M.S.



268 BULLETIN FLORIDA STATE MUSEUM Vol. 11

0 + V

1 I

Figure 4.-Nests of Chaetura brach!/ura.



1967 COLLINS: SWIFTS OF TRINIDAD 269

characteristic of petagica nests ( Fischer, 1958: Fig. 8), and the ab-
sence of this additional support may account for their more rapid de-
struction. Egg laying starts about 10 days after the beginning of
construction and before the nest is completed. The nests are unlined,
but in two cases a feather was glued in among the sticks, and one nest
containing recently hatched young had a large white feather in the
bottom.

A variety of other organisms also occupied the manhole nest sites.
Those that were partly Elled with water usually contained the tree
frog Hyla rubra. An unidentified snake and a lizard, Ameiva ameiva,
were each seen once at the bottom of dry holes, presumably having
entered 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

4
top and the globular mud nest of the potter wasp ( Eumenes canalicu-
latus) on the walls. Spiders of several types frequented the manholes,
and Snow ( 1962) once saw a large spider (Mygale sp.) pounce on
and kill a nestling that fell out of the nest.

NESTS OF THE GENUS Cupseloides

The nests of 4 of the 10 species presently included in the genus
Cypseloidesi are still unknown. Those that have been described, how- +
ever, show a good deal of similarity in both site and material. 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 ( 1961) postulates five -eco-

"logical requirements for nest sites: the presence of water, high re-
lief..., inaccessibility to terrestrial marauders, darkness, and the
lack of fiyway obstructions in the vicinity of the nest." This type of
nesting situation is so characteristic that many nests of nigel· have been
found by searching for these "ecological requirements" rather than for
birds showing signs of possible breeding ( Michael, 1927; Knorr, 1961,
1962 ). I used the same procedure to find additional rutilus nest sites
in Trinidad, and I venture it might be applied with equal success in
locating the yet undescribed nests of Cypseloides biscutatus ( Sclater),
cherriei Ridgway, crypms Zimmer, and lemosi Eisenmann and Leh-

i Until more detailed information is available I feel it is best to include the
species of Aeromis, Nephoecetes, and Streptoprocne in the genus C!/psdoides as
proposed by Lack ( 1956a).



270 BULLETIN FLORIDA STATE MUSEUM Vol. 11

mann. Certain nests attributed to C!/pseloides do not conform to this
general pattern or the descriptions of other nests of the same species.
One attributed to fumagatus ( Streubel) by Holt, ( 1927-1928) and one
to zonaris ( Shaw ) by Todd and Carriker ( 1922) were both described
as being made of twigs glued together with salvia. The nest attributed
to fumigatus contained five young and was located inside a house
gable, an improbable site and brood size for a Cypseloides species.
Both nests were probably made by some species of Chaetura.

Also Cupseloides semicollaris lays its eggs on sandy ledges in
caves ( Rowley and Orr, 1962) and zonaris was once suspected of
nesting in burrows in a cliff in Guatemala ( Anthony, in Griscom,
1932:194), certainly an atypical site for any New World swift. In
Africa, however, Apus horus ( Heuglin) characteristically nests in
the deserted burrows of bee-eaters and swallows ( Harwin, 1960;
Steyn, 1966).

1

S

Figure 5a.-Cone-shaped nest of Cypseloides rutilus.



1967 COLLINS: SWIFTS OF TRINIDAD 271

Cypseloides rutilus.-In the first description of a rutilus nest, Orton
( 1871) states ones in Colombia were "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... made of various plant fibers, usually including some
moss.

My observations show some variation in the shape of rutilus nests.
Some nests built on smooth vertical surfaces resembled truncated
cones ( Fig. Sa) similar to those reported for rutilus in Mexico by
Rowley ( 1966) and for fulnigatus and zonaris in Argentina by Dab-
bene ( 1918) [cited by Lack ( 1956a) as Reborati, 1918]. Others,
located on small rock ledges, were little more than pads of nest ma-

1 L

.r

....
f

.' r ...
42

....
4

- *i ,

Figure 5b.-Disc-shaped nest of C!/pseloides rutitus.



272 BULLETIN FLORIDA STATE MUSEUM Vol. 11

terial, somewhat thicker along the outer rim, with a wide but shallow
cup for the eggs ( Fig. 5b). This type of nest closely resembles the
"disk-shaped" ones reported for zonaris and niger when similarly 10-
cated on damp rocky ledges ( Rowley and Orr, 1965; Michael, 1927).
The shape of the nest thus seems somewhat dependent on whether it
is afGxed to a smooth rocky surface or perched on a narrow ledge.
Larger species such as zonaris require greater support for their nests
and consequently would be expected to build on ledges. The smaller
and lighter weight species such as rutilus and fumigatus can also build
cone-shaped nests fixed to vertical surfaces. Presumably owing to its
extreme weight ( 170-180gl, 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, rutilus nests in Trinidad appeared to
be primarily of soft plant material with some mud intermixed. This
mud presumably helps hold the nest material together and amx it
to the rock as no salivary glue appeared to be used. The universal
us of saliva in swift nest construction has already been questioned
( Marshall and Folley, 1956; Johnston, 1961), and its use should not
be assumed for rutilus until further information is available. The
plant materials used in Trinidadian rutitus nests included a liverwort
of the genus Plagiochilax, the lycopsids Selaginella cladorrhizans
and S. cf. arthritica, and the filmy fern Trichoinanes membranaceum.
All of these plants grow in damp shady places, particularly on rocky
outcrops along streams ( Fig. 6) and thus in proximity to the nest
sites of these swifts.

No information is available on the collection of the nest material
or nest construction by any species of Cypseloides. Nests are used
several successive years; a new lining of fresh green material is
added annually, and the annual additions show as distinct layers.
Sea cave nests of rutilus appeared to be constructed of slightly
different materials and contained seaweed as reported for a similarly
located nest of niger ( Legg, 1956).

In Trinidad rutilus nests have been found on rocky outcrops
overhanging pools in mountain streams ( Fig. 7), on the rocky walls
of a river gorge, in sea caves, in man-made culverts ( Fig. Sa) and
in one case on the under side of a bridge ( Belcher and Smooker,
1936; Snow, 1962). Of the 15 nest sites observed during this study,
2 were along mountain streams, 6 were in a river gorge, 4 in sea

i Weight data obtained from two specimens in the U. S. National Museum.



1967 COLLINS: SWIFTS OF TRINIDAD 278

f
Ic * -79-

P

YE

Figure 6.-Nesting material of Cypseloides rutilus gi-owing en stream-side rock
ledge.

caves, and 3 were in man-made culverts under a road or under a
bridge; 9 of these sites were ones found earlier by Snow ( 1962).

All the sites were similar to those for other Cypseloides species
in being in deep shadow, inaccessible to terrestrial animals, and



274 BULLETIN FLORIDA STATE MUSEUM Vol. 11

closely associated with water. They did not agree with all the
"requirements outlined for niger in that they were rarely associated
with high relief. All were in forested areas at relatively low eleva-
tions from sea level to 1100 feet. Most nests were in deep shadow
and none received direct sunlight. Streamside nests were only 2-4

Figure 7.-Stream nesting habitat of Cypseloides rutilus, Arima Valley,
Trinidad.



1967 COLLINS: SWIFTS OF TRINIDAD 275

feet above the water, but nests in a gorge were as much as 25
feet above the river where the walls were still damp from seepage
water. The sea-cave nests were about 6-8 feet above either permanent
watef or tidal wash. In Mexico, Rowley ( 1966) found nests of
rutitus in cayes in a rocky escarpment along a stream and also on
the vertical walls of a river gorge from 18 inches to about 15 feet
above the water level; in both situations the nest sites were in deep
shadow.

In contrast to the nests of the larger species, zonaris and niger,
which nest near and sometimes behind waterfalls, only one Trini-
dadian rutilus nest was near falling water. This nest, on a smooth
wall about 8 feet above a pool into which a small waterfall poured,
was just outside the spray zone of the fall. However Rowley ( 1966)

«noted a stream of water cascading partially over the entrance" of
a nesting cave of rutilus in Oaxaca, Mexico, and Lowery and Dal-
quest ( 1951) collected adults roosting in a cave behind a waterfall
elsewhere in Mexico.

The largest concentration of nests was in the rock-walled Guacharo
Gorge cut into limestone by the Arima River near the head of
Arima Valley. This gorge on the Spring Hill Estate has been a
nesting place for these swifts for at least 40 years, Belcher and
Smooker ( 1936) having reported a nest there in 1926. Occupied
nests were situated along the gorge at varying intervals, the shortest
being about 35 feet. Elsewhere the least distance I have recorded
between active rutilus nests was about 7 feet, which was all that -
separated two nests on the walls of a cave-like rock archway 8
feet above a channel cutting through Saut D'Eau Island, an islet
off the north coast of Trinidad. It is worth noting that these swifts
had to cross about a quarter mile of ocean to reach their nearest
feeding ground. The swifts inhabiting sea caves on Huevos Island
also probably cross stretches of water to reach mainland feeding
areas.

In Oaxaca Rowley ( 1966) found four rutilus nests at varying
intervals along a mile-long river gorge and clusters of nests in two
small shallow caves. One cave, approximately 25 feet deep, 10 feet
wide, and 15 feet high, contained 5 old nests, while the second
cave, about the same size but with a higher ceiling, contained 6
occupied nests.

The most prominent organisms sharing these nest sites were bats
( mostly of the family Phyllostomidae) that used the shady areas
as daytime roosts, several species of small frogs, and a cave cricket.



276 BULLETIN FLORIDA STATE MUSEUM Vol. 11

I once caught a small snake, Leptodeira annulata, 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 "guacham"
or oilbird ( Steatornig caripensis) as did two of the sea caves men-
tioned earlier in which rutilus was thought to nest (Snow, 1962).

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

BREEDING SEASON

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 Ch. brachyura and Cyp. rutilus extend
from April until August or early September, but varying within this
period considerably from year to year. The season coincides with
the height of the annual rainy season when insects are presumably
most plentiful. This probably represents an adaptive synchroniza-
tion that assures both an adequate supply of food when females
are forming eggs and when young are to be fed ( Thompson, 1950;
Lack, 1954, 1966 ). A similar adaptive relationship seems to exist
in Trinidad with the swallows, which also depend upon flying insets
for their food ( Snow and Snow, 1964).

Although the ultimate factor regulating the breeding season
seems to be an abundant food supply to support egg production
and nestling growth, the proximal, or triggering environmental
factors are more obscure. The role of the photoperiod in controlling
breeding id tropical and equatorial birds is still subject to debate.
Experimental work has shown that the gonads of several low-
latitude birds will respond to increasing photoperiod ( Marshall and
Disney, 1956; Miller, 1959), as has been demonstrated for many
temperate latitude species. However, the small annual change in
photoperiod at the lower latitudes make it more reasonable to assume
that these swifts, and possibly other tropical birds, respond to a
combination in photoperiod and some more variable environmental



1967 COLLINS: SWIFTS OF TRINIDAD 277

stimulus as Tordoff and Dawson ( 1965) showed for the erratic
breeding of the Red Crossbill, (Loria curuirostra). This crossbill
shows only a partial response to increasing or constant long photo-
periods; the completion of gonadal development and the triggering
of breeding depends on some proximate environmental factor, such
as an increased availability of suitable food.

The most obvious environmental factor regulating the breeding
of these Trinidadian swifts is the onset of the annual rainy season.
Yet the responses of the two species differ somewhat. Ch. brachyura
usually begins nesting before Ct/p. mtilus. and very soon after the
Brst heavy rains of the season. The Brst 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 years when brief heavy rains
preceed the period of intense summer rainfall, brachyura may start
nesting even earlier. In 1959 heavy rains early in April were followed
by a dry spell that lasted until the onset of the true summer rains
in mid-May. This false start triggered breeding by brachyura in
April, followed by a lull during the dry spell, and a renewal of
nesting activity in late May (Snow, 1962). During the extremely
wet winter and spring of 1964 brachyura began breeding very early,
although the main rainy season did not start until late May. A
summary of the number of brachyura nests begun in the years
1957 to 1964 in half-month intervals is presented in Table 2. Several

TABLE 2. BREEDING SEASON OF Chaetura brachqura. Figures show number

of nests started during half-month intervals.
A 11

Period 1957* 1958* 1959* 1960° 19610 1962 1963 1964 Years

1-15 April 1 1 2
16-80 April 1 1 8 2 7

1-15 May 541 8124424
16-81 May 4 8 2 8 2 1 2 4 21
1-15 J une 1 4 8 4 2 14

16-80 J une 115124 1 · 15
1-15 July 8 2 1 3 8 1 13

16-31 July 1 4 2 1 1 1 00 1 11
1-15 Aug. 8 1 2 3 1 00 1 11

16-81 Aug. 3 1 00 4
1-15 Sept. 1 1 1 00 8

TOTAL 19 16 16 14 21 18 12 14 125

*Data from Snow ( 1962 )
00 No observations.



278 BULLETIN FLORIDA STATE MUSEUM Vol. 11

other Trinidadian birds appeared to be influenced directly 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 activites
in several species. Similar dramatic shifts in breeding activity
associated with rainfall levels have been noticed also in nearby
Venezuela ( Gilliard, 1959).

Cyp. rutilus started its breeding activities later than Ch. brachyura
and in most years showed a greater population synchrony ( Table 3).
The first sign of renewed nesting was always the appearance of a
fresh lining of greenery in the old nests in preparation for their
re-use. Before the rains start this material ii in short supply, for
it dies away during the dry season and only regains its lushness
when the rains return. Cyp. rutilus apparently awaits the reappear-
ance of suitable nest material to begin its breeding cycle. Such
plant material is in turn dependent on the return of the full summer
rains and, in some cases, on the rising of water levels in the streams.

This sequence of events was particularly noticeable when eastern
Trinidad experienced a very wet winter and spring in 1964. As
mentioned earlier, this unseasonable wet weather stimulated very
early breeding by Ch. brach!/ura. At the same time Arima Valley
experienced a fairly normal dry season, which did not end until

TABLE 8. BREEDING SEASON OF C!/pseloides rutilus. Figures show number
of nests started during half-month intervals.

All
Period 19570 19580 19590 19600 19610 1962 1968 1964 Years

1-15 April
16-80 April 1 1
1-15 May 1 1 1 3

16-81 May 1 1 2 1 5 6 16
1-15 J une 11 2 3 5 1 13

16-30 June 1 2 1 2 6
1-15 July 2 1 8

16-31 July 2 1 2 1 2 00 8
1-15 Aug. 1 1 1 2 1 1 ** 4 11

16-31 Aug. 1 8 2 00 2 8

TOTAL 2 9 7 8 9 11 10 13 69

*Data from Show ( 1962)
0* No observations



1967 COLLINS: SWIFTS OF TRINIDAD 279

nearly continuous heavy rains fell on 22-23 May. Prior to this time
no indication of breeding was apparent at any known C!/P. rutilus
nest site in the valley; the stream -water levels were low, and no
suitable nest material was available. A few days after these first
heavy rains the mossy stream-side plant life recovered a great
measure of its former lushness. On checking six rutilus nest sites
on 29 May I found all six nests 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 sixth nest, though relined, was not used that year.

CLUTCH SYE

Chaetura brachgura
Like other species of Chaetura swifts, brachyura lays compara-

tively large clutches. The 26 complete clutches observed from 1962
to 1964 ranged from 2 to 7 eggs, with a mean clutch size of 3.8
( Table 4). This is slightly less than in the other Chaetura species
for which data are available ( 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 both
pelagica and brachyura, but each case appeared to result from two
females laying in the same nest ( Fischer, 1958; Snow, 1962). The
7-egg clutches recorded for vauxi ( Baldwin and Zaczkowski, 1963)
and brachyura ( this study) both seemed to be the product of but

TABLE 4. DISTRIBUTION OF CLUTCH SIZES OF Chaetura bracht/ura By HALF-
MONTH INTERVALS FOR YEARS 1962 To 1964.

Clutch Size
Period 128 4567 Totals

16-80 April 1 1 2

1 -15 May 1 2 2 5
16-81 May 11 8 1 6
1-15J une 

1 
116-80 June 8 1 1 4

1 -15 July 2 1 1 4
16-31 July 1 1 2
1 -15 Aug. 1 1
16-81 Aug. 1 1

All months 0 8 8 8 5 1 1 26



280 BULLETIN FLORIDA STATE MUSEUM Vol. 11

TABLE 5. CLUTCH SIZE OF SWIFT SPECIES IN THE GENUS Chaetura.

Number clutch
of Average

Species clutches Range size Reference

C. pelagica 25 2-5 4.2 Fischer, 1958
27 8-7 4.0 Dexter ( in Fischef, 1958)
19 4-6 5.3 Sherman, 1952

C. brachgum 41 1-6 3.6 Snow, 1962
·26 2-7 3.8 this study

C. andrei 8 4-5 4.6 Sick, 1959
C. vauxi 7 3-7 ? Baldwin & Zaczkowski,

1968; Bent, 1940.

a single female and in both 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 brach!/ura in 1963. In this case a clutch of 4 eggs was laid
in a newly constructed nest between 7-13 May, and the clutch still
consisted of only 4 eggs on 17 May. On 21 May a fifth egg was
noticed and when the nest was checked on 23 May a sixth had been
added. Four 2-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 on the same day dead or nearly
dead on the floor of the nest cavity. Presumably they were inadvert-
ently 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 dis-
ruption of egg laying and ejection of eggs in two other cases. Adult
birds were frequently observed roosting in nest cavities with a nesting
pair, though not in close approximation. At three other nests extra-
parental cooperation was observed in the feeding of the young.

In Ch. pelagica extra-parental 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 show it to be of
regular occurrence in brachyura. The origin of such cooperation is not
clear. It may result from a shortage of nest sites as Snow ( 1962)



1967 COLLINS: SWIFTS OF TRINIDAD 281

suggests, from the inability of some birds to find mates as Dexter
( 1952) proposes, or to some other cause. Skutch ( 1961) feels that
such activities in passerine birds may represent an adaptive curtail-
ment of the reproductive rate favoring the greater survival of fewer
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 partially incubated in a single
clutch weighed 1,1,1, 11/4, and 11/& grams. The range in size of
seven eggs was from 17 to 18% mm in length and from 12 to 13 nim
in width. They lacked any appreciable taper. Fresh eggs were a pure
white; well incubated ones were at times slightly discolored.

Cypseloides rutilus
As in all Cypseloides swifts, clutch size in rutitus is very small. Of

25 clutches  observed from 1962 to 1964, 23 were of 2 and 2 of 1 egg,
the average clutch size being 1.9. Of 32 clutches Snow ( 1962) ob-
served only one case of a clutch of a single egg was noticed and that
seemed attributable to a bird breeding for the first time.

The interval between the laying of the two eggs was slightly more
irregular than for brachyura. The second egg of the clutch was
usually laid 2 days after the first, but occasionally an interval of as
much as 5 days occurred, during which the first egg was left un-
covered.

The eggs from two clutches weighed 21/4, 2%, 2% grams and,
like those of brach!/ura, were white and became noticeably discolored
during the course of incubation. The one egg of rutilus measured in
Trinidad was 20.5 mm long and 15 mm wide and lacked any appreci-
able taper. Clutches Rowley ( 1966) measured in Mexico ranged from
23.5 by 15.2 mm and 24.2 by 15.0 mm to 22.6 by 15.2 mm and 21.9
by 15.4 mm.

No extra-parental cooperation was observed in this species.

INCUBATION AND HATCHING SUCCESS

The incubation period was calculated from the laying of the last
egg to the hatching of the last young. For Ch. brachyum the 17-18
day period determined by Snow ( 1962) was confirmed, except in one
case when the period was only 16 days. Hatching of the entire clutch
usually involved a period of 48-72 hours between the hatching out of
the first and last young.



282 BULLETIN FLORIDA STATE MUSEUM Vol. 11

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

Although substantial losses often occurred during the incubation
period, the percentage of hatching was high among those eggs of
both species that reached the expected date of hatching ( Table 6).
The figure recorded in this study for rutilus ( 84.3 per cent ) is lower
than that of Snow (93.1 per cent) because of the desertion of a
clutch, which may in turn have resulted from the greater frequency
of disturbing visits in this study. Thus the higher value is probably
more characteristic of undisturbed nests. The hatching rate based on
the total number of eggs laid is rather low for both species compared
with similar values reported for other swifts ( Table 6). Comparable
data for tropical congenors is however lacking. Those species show-
ing a high hatching success are also those with the more inaccessible
nest sites. The higher hatching success of Cyp. rutilus Eis compared
to Ch. brachyura probably similarly reflects the fact that Cyp. mtilus
nests overhang water on smooth surfaces or inaccessible ledges, and

Table 6. AVERAGE HATCHING AND FLEDGING SUCCESS OF SWIFT SPECIES

Eggs hatched of Eggs hatched Young fledging Young Redging
Species No. completely of No. laid of No. eggs of No. eggs

incubated (%) (%) hatching (%) laid (%)
Apus apusl

( England) 74.011 74.5 59.0
Apus apus2

( Switzerland ) -- 76.0 85.8 65.2
Apus melba3 94.4 86.0 80.9 76.0
Apus cafet 98.9 88.6 86.0 76.2

( Kenya)
Apus cal]ee 81 .0 70.3 57 .0

( South Africa)
Cypsiurus parvt,56 - - 54.2 31.5 17.1
Chaetura pelagica7 89.5 96.1 86.0
Chaetura brachqura8 95.0 51.7 58.5 26.7
Cypseloides rutiluso 93.1 --
Cypseloides rutiluss 84.8 65.8 68.4 86.1
Collocatia maximalo 29.2 65.4
Collocatia esculentalo - - 76.1 74.7
Collocalia salanganalo 51.5 78.5

1Lack and Lack, 1951, 2Weitnauer, 1947. BLack and Arn, 1947. 4Moreau,
1942a. 5Schmidt, 1965. eMoreau, 1941. 7Fischer, 1958, 8This study. 9Snow,
1962. 10Medway, 1962a. 1178.0 per cent when eggs ejected prior to start of
incubation are omitted.



1967 COLLINS: SWIFTS OF TRINIDAD 288

are less often disturbed by predators than the nests of Ch. brach!/ura
in manholes or hollow trees. Several of the "inaccessible" sites men-
tioned for other species were in man-made structures and may not
reflect mortality rates when under natural conditions.

PARENTAL CARE

The period when 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 brach{/ura the nestling and
fledgling periods are well defined while in rutilus the two periods
overlap.

Chaetura brachgura
Nestling period.-The young of brachyura spend the Erst 3 weeks

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

Fledgling period.-The brach!/ura fledgling period lasts about 2
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 49 and 50 days after hatching respectively.

The ultimate factor governing departure of the fledglings is
probably 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 that escaped while being handled flew away
successfully, and 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 abandoning the nest
cavity entirely. Two 35-day-old swifts, caught roosting in their
nest cavity, were fully capable of sustained flight at this age and



284 BULLETIN FLORIDA STATE MUSEUM Vol. 11

returned successfully when released at a point 9 miles away.
The earlier obseryations by Snow ( 1962) indicated that "the young
can fly if disturbed as early as 28 days after hatching; if undis-
turbed, they do not usually leave until they are 30-40 days old."
Cypseloides rutilus

In Cup. rutilus, as in all swifts except species of Chaetura, no
separation of the hestling and fledgling periods is apparent, as the
young remain in the nest until the time they can fly and feed them-
selves. This combined nestling-fledgling period in Cyp. rutitus is
somewhat longer than in Ch. brachyura, being closer to 40 days.
All available figures exceed 35 days, and most fall between 37-43
days. These figures are in agreement with those determined by
Snow ( 1962). Young rutitus have been seen on occasion to exercise
their wings while "hanging to the outer rim of the nest" ( Snow,
1962). Any attempt to clamber about on the rocky wall adjoining
the nest might be fatal, as these surfaces are usually smooth and
often wet and slippery.
OTHER SPECIES

The combined nestling-fledgling periods for most swifts are be-
tween 35-45 days, with larger species requiring slightly longer periods
than smaller ones. Unusually short periods of 29-32 days were noted
for Cypsiurus parcus C Litchenstein ) and 30 days for Chaetura
pelagica ( Moreau, 1941; Fischer, 1958). Slight geographic variation
in the nestling-fledgling period has been noted in Apus ca#er
( 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 the 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. After two weeks time
the young are too large for the adults to cover effectivley. During the
first days of nestling life brachyura nestlings are brooded regularly
by day for long periods and for shorter periods up to 20 minutes long
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 rutilus are usually brooded
continuously during the daytime for the first 10-11 days, and occa-
sionally as late as 13 days after hatching.



1967 COLLINS: SWIFTS OF TRINIDAD 285

Most swift species brood during the daytime for most of the Brst
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 Lack and Lack
( 1952) record daytime brooding 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.

FLEDGING SUCCESS

The mortality during the nestling and fledgling periods for Ch.
brachyura was approximately equal to that during incubation ( Table
6). Only 53.5 per cent of the 58 hatching fledged successfully, and
only 26.7 per cent of the 112 eggs laid resulted in fledged young. For
C!/p. rutilus the mortality rates of eggs and nestlings were also about
equal, with 68.4 per cent of the 19 hatchlings fiedging successfully, or
36,1 per cent of the total 36 eggs laid. -

As indicated by Snow ( 1962), the figures for brachyura may not be
typical of nests other than in man-made structures, and some addi-
tional mortality may well have resulted from the frequent visits and
repeated handling that were part of this study. No information is avail-
able for any species of Chaetura in a natural nest site. The only in-
formation on other Cypseloides swifts is for niger, which had a simi-
larly high rate of nest failures, particularly in the nest:ling stage
( Hunter and Baldwin, 1962).

The causes of egg and nestling losses are not clear. At least one
niger nestling was seen to fall from the nest ( Knorr, 1961: 168), and
possibly many of the rutilus losses are similarly due to young birds
accidentally falling out of the nest. This is less likely in brachyura
nestlings because their strong feet enable them to hold tenaciously to
the nest at a very early age.

No predation of eggs or nestlings was actually observed for either
species. Two nestlings brachyura and one of rutilus were found that
had been badly chewed by some animal. As these nests were inacces-
sible to terrestrial predators, possibly the culprits were bats of one of
the several species that commonly roosted close to the swift nests.
Other losses of both nestlings and eggs might also be attributable to
bat predation. Skutch (1964) suspected bats to be responsible for
the disappearance of eggs and nestlings and for the wounding of a
nestling hermit hummingbird.

In recent studies of three species of Cypseloides swifts in Mexico,
including rutilus, numerous broken eggs were found amid the litter



286 BULLETIN FLORIDA STATE MUSEUM Vol: 11

that accumulated under nests and roosts ( Rowley, 1966; Rowley and
Orr, 1962, 1965). Altough some of these may have been dropped by
females, particularly early in the breeding season, most were probably
accidentally ejected from nests by adults. Rowley ( 1966) considered
rutilus "clumsy on [their] nests" and that consequently eggs were
often accidentally rolled over the edge of the shallow nests and des-
troyed. Accidental ejection of eggs from a nest by an adult has been
observed in Chaetura brachyura ( pers. obs.) and in two species of
Apus (Lack and Lack, 1951; Moreau, 1942a).

GROWTH

BODY WEIGHT
A total of 321 brachyura nestling weights was obtained in the field,

from 57 chicks in 15 nests ( Fig. 8); from 1-15 weights were obtained
from single nestlings. A total of 165 weights of rutilus nestlings was
obtained from 25 individuals weighed between 1 and 16 times each
( Fig. 9).

At hatching the average weight of brachgura nestlings was 1.6
grams; 18 days later they reached a maximum average weight of 21.2

25-

20·

15-

9-
8-
7-
6.

W
L 

IN
 

G
R

AM
S

5-

4- CHAETURA BRACHYURA
3- f
2-

024681012141618202224 26 28 30 32 34 36
AGE IN DAYS

Figure 8.-Growth curve of Chaetura brachyura. Semi-log plot, vertical lines
represent range of daily  weights, curve connects daily means.



1967 COLLINS: SWIFTS OF TRINIDAD 287

grams, a 13.3-fold increase. At fiedging they had reached approxi-
mately 87 per cent of their adult weight.

The average weight of rutilus at hatching was 2.1 grams, and they
reached a maximum average weight of 26.2 grams on day 29, a 12.4-
fold increase. At fledging rutilus weighed approximately 119 per cent
of their adult weight.

The instantaneous percentage growth rate calculated for each day
( Brody, 1945: 508) tended to decrease in both species after an initial
rise ( Table 7,8). Ch. brachgura had its peak growth rate on the 4th
day after hatching, but the peak for rutilus did not occur until the 7th
day. The average weight gain per day and the average per cent
growth rate per day calculated for seven 5-day periods during the
nestling life of these two species ( Table 9) show that brach!/ura
has an initially higher average daily weight gain and average per cent
growth rate that subsequently decline rapidly. After approximately 3
weeks of nestling life the young begin to lose weight, particularly
when they first leave the nest and again later when they begin to
fly. Cyp. rutilus, on the other hand, has an initially lower average
daily weight gain and average per cent growth rate which also
declines, although at a slower rate so that the nestlings do not begin

15-

10-
9-
8
7-
6-

W
T.
 I

N 
G

R
AM

S

5-

4- GYPSELOIDES RUTILUS

3-

2-

024681012141618 20 22 24 26 28 30 32 34 36

AGE IN DAYS

Figure 9.-Growth curve of Cypseloides rutilus. Semi-log plot, vertical lines
represent range of daily weights, curve connects daily means.



288 BULLETIN FLORIDA STATE MUSEUM Vol. 1 I

Table 7. DAILY WEIGHT ( GRAMS) AND RELATIVE GROWTH RATE (PER CENT) OF
Chaetura brach!/ura.

Mean Per cent
Days from Mean weight relative growth
hatching No. weight Range change per day

20 1.6 1 - 2% --„.
1 18 2.1 lA - 2% 0.5 27.1
2 18 2.8 234 - 8% 0.7 28.7
8 10 - 3.7 21% - 442 0.9 27.8
4 10 5.1 8% - 6% 1.4 34.0
5 10 6.8 5% - 7% 1.2 19.1
6 8 7.4 6 - 9 1.1 16.0
7 9 8.7 4 - 11 1.8 16.1
8 16 11.1 844 - 15 2.4 24.8
9 9 11.2 536 - 15 0.1 0.8

10 15 18.5 11~6 - 16% 2.8 18.6
11 14 16.1 18 - 19% 2.6 17.6
12 14 16.2 1836 - 19 0.1 0.6
18 7 18.3 15 % - 20 2.1 12.1
14 9 19.0 17% -21% 0.7 3.7
15 11 18.1 18 - 22% -0.9 - 8.6
16 8 19.1 1716 - 21% 1.0 13.9
17 7 19.6 18 - 22 0.5 2.5
18 6 22.2 17%- 2236 2.6 12.4
19 7 20.2 1736 - 28% -2.0 - 9.4
20 5 20.9 19% - 23 0.7 3.4
21 7 20.2 17% - 22% -0.7 -3.4
22 6 19.0 17% - 22 36 -1.2 - 9.5
28 5 18.9 16 - 21 -0.1 - 0.5
24 8 18.8 13% - 21% -0.1 - 0.5
25 11 19.7 16 - 21 0.9 4.6
26 7 19.0 1536 -2134 -0.7 -3.6
27 7 19.4 17% - 28 0.4 2.0
28 6 18.0 17 - 20 -1.4 - 7.4
29 6 18.7 17% -21% 0.7 8.9
30 6 18.4 1634 - 2014 -0.8 - 1.6
81 7 16.5 1444 - 18 42 -1.9 -10.8
82 8 17.0 16 - 181/2 0.5 2.9
83 5 16.6 15 - 17% -0.4 - 2.8
84 4 15.7 14 14 - 17 -0.9 - 5.5
85 4 15.4 18 - 17 -0.8 - 1.9
36 1 16.0 0.6 8.8
87 2 14.8 1836 - 15 -1.7 -11.2



1967 COLLINS: SWIFTS OF TRINIDAD 289

Table 8. DAILY WEIGHT ( GRAMS ) AND RELATIVE GROWTH RATE (PER CENT) OF

C!/pseloides rutilus.

Mean Per cent
Days from Mean weight relative growth
hatching No. weight Range change per day

0 7 2.1 2 - 242
1 10 2.5 2 - 8 0.4 17.4
2 7 8.5 2% - 4% 1.0 38.6
8 10 3.9 844- 5 0.4 10.8
4 8 5.0 4% - 6% 1.1 24.8
5 18 6.8 542- 7% 1.8 28.1
6 7 7.8 642- 8% I.0 14.7
7 7 10.6 8 - 14% 8.8 88.2
8 4 9.8 842 - 12% -0.8 - 8.7
9 10 11.6 8 - 13 1.8 16.8

10 8 12.8 9% - 1444 1.2 9.8
11 7 14.1 1142 - 16 1,8 9.6
12 6 15.8 14 - 1842 1.7 11.8
13 .6 16.6 14 42 - 17% 0.8 4.9
14 4 18.2 17 - 19% 1.6 9.2
15 1 20.5 2.8 11.9
16 6 20.7 1842 - 2142 0.2 0.9
17 1 19.8 -1.4 - 7.0
18 6 21.0 20 - 22 1.7 8.4

e &
 . 

8.,
8 s

.5.5
1 4 21.2 18 - 26% 0.2 9.8

4 28.9 216 - 24% 2.7 11.9
6 22.5 18% - 26 -1.4 - 6.0
2 20.8 2014 - 21% -1.7 - 7.8
8 25.5 25 -27 34 4.7 20.3
1 23.0 . -2.5 -10.3
3 25.2 24% - 25% 2.2 9.1

27 3 24.2 24 - 25 -1.0 - 4.0
28 1 24.0 . -0.2 - 0.8
29 3 26.2 2314 - 28% 2.2 8.7
30 4 23.6 221,6 - 26 14 -2.6 -10.4
81
82 1 20.3 4.1 -15.0
83 .... -8.8
84 8 24.4 28 - 2656 -- 18.3
55 1 24.0 ........ - ........ -0.4 - 1.6
86 2 23.9 2236 - 25% -0.1 - 0.4
87 1 24.8 0.4 1.6



290 BULLETIN FL,ORIDA STATE MUSEUM Vol. 11

Table 9. AVERAGE DAILY GROWTH RATE < GRAMS ~ AND RELATIVE GROWTH RATE
(PER CENT ~ FOR 5-DAY INTERVALS FOR Cupseloides rutitus AND Chaetura brach-

vura.

C. brach!/um 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 -0.8 - 2.1 0.4 1.6
25-29 -0.02 - 0.1 0.8 8.8
80-84 -0.6 - 8.5 -0.4 - 2.8

to lose weight until approximately 41/5 weeks after hatching.
The general pattern of growtli shown by these two swifts is similar

to that reported for most altricial birds, particularly those with longer
periods of development ( Dawson and Evans, 1957, 1960; Maher,
1964; Kahl, 1958). Ch. brach[/ura is nearly identical in growth pattern
to the only previously studied Chaetura species, pelagica and uauxi
( Fischer, 1958; Baldwin and Zaczkowski, 1963). Cyp. 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, brachyura and rutilus hatch
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 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 hatching. 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. 10 and the tail in Fig. 11. The tail completes its
growth about 26-27 days after hatching, but the wing does not reach
full length until shortly after Redging.



1967 COLLINS: SWIFTS OF TRINIDAD 291

120-

W
IN

G
 L

EN
G

TH
 I

N 
M

M 90-

C. BRACHYURA

60-

C. RUT]LUS

30-

15- A-- 1

0 1, 1,
0 5 10 15 20 25 30 35

AGE IN DAYS

Figure 10.-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=

.

40-

35- 1 ,

i *
Z 30-

TA
IL
 L

EN
G

TH
 I

N C. BRACHYURA
25-

20-

4· G. RUTILUS15-

10-

5-

0 6'6'4'68,6 15 20 25 30' 35
AGE IN DAYS

Figure 11.-Growth of tail of Chaetura brachyura and Cypseloides rutilus.
Vertical lines represent ranges, curves connect daily means.



292 BULLETIN FLORIDA STATE MUSEUM Vol. 11

Cyp. mtitus acquires its feather covering in a sequence generally
similar to that of Ch. 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 at about day 10-11.
The flight feathers begin to emerge from their sheaths about 13-14
days after hatching, about one day later than noted for brachgura. The
contour feathers, however, begin to break through their sheaths much
earlier in rutilus despite their having emerged through the skin some-
what later than in brachyum. These feathers begin to erupt in 13 days
as opposed to day 15-16 for brachyura. The contour feathers of rutilus
on the cervical, capital, and ventral tracts develop somewhat more
slowly than those of the dorsal tract, as also noted for brachyura. The
tail reaches its full length about the time the young fiedges (Fig. 11),
but the wing does not complete its growth until early in the post-
fledging period ( Fig. 10).

A major difference in the plumage development of Chaetura and
Cypsetoides 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 consists 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 previ6us estimate of 8-9 days after hatching.

These semiplumes are freed of their sheaths for more than half
their length shortly after they erupt from the skin, and thus the nest-
ling 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
over by the emerging contour plumage at about 28 days after hatch-
ing. 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 occasionally a few appear along
the lateral margin of the humeral tract and in a short row in the apter-
ium 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 one probably occurs in all members of the genus. The semiplume



1967 COLLINS: SWIFTS OF TRINIDAD 298

covering and the early emergence of the contour feathers from their
sheaths appear to be aids to thermoregulation in nestlings living in a
cooler microclimate.

Eyes.-The two species differ noticeably in the development of the
eyes. Those of Chaetura are partially open on day 16 and completely
open on day 18, which is slightly later than has been observed for
pelagica and uauxi ( Fischer, 1958; Baldwin and Zaczkowski, 1963).
In Cypseloides rutilus they open gradually with an interval of more
than a week between the first partial and the complete opening; the
eyes may open partially as early as day 7, but usually this first occurs
on· day 8-9; they are not fully open until about day 16-17.

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 pig-
mentation at the tip, especially noticeable in brachgura. The lining of
the mouth is also a flesh pink and lacks the bright pigmentation ob-
served in many other avian groups, particularly the passerines. A
prominent egg tooth is present on the upper mandible. Parkes and
Clark ( 1964) report similar structures in other genera and the lower
mandible has a hardened whitish cap. The egg teeth gradually disap-
pear during the first weeks of nestling life. Both egg teeth are gen-
erally unobservable by day 14, although a slight roughness on the cul-
men 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 brachyura seem to be particularly well
developed very early in life and are capable of supporting the nestling
on a vertical surface within 48 hours of hatching. The feet of rutilus
cannot support a nestling this way until about day 14. Michael ( 1933)
similarly notices that Cypseloides niger has "the dainty feet and slen-
der 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
on the particularly sharp claws and strong toes as compared to
Cypseloides niger. The young of brachyum hold on to the twigs of
the nest so tenaciously that claws are apt to be pulled off it care is not
taken in removing them from the nest. An unexplained loss of claws
of vauxi nestlings noted by Baldwin and Hunter ( 1963) probably
occurred during their removal from the nest for observation. Their
stronger feet enable to Chaetura species to raise larger broods in
their small nests. The ability to hold tightly to the nest reduces the
chances of a nestling being jostled out of the crowded nest, parti-
cularly when defecating. As the nestlings grow and overcrowd the



294 BULLETIN FLORIDA STATE MUSEUM Vol. 11

4

Figure 12.-Chaetura brachuura nestlings shortly before leaving the nest.

nest. ( Fig. 12) they can climb out and cling to the wall nearby until
actual fledging (Fig. 13).

Behavior. The vocalizations of these nestling swifts are rather
limited. Cypseloides rutilus nestlings only make a very soft twittering
when disturbed and practically no noise during feeding, but brachgura
nestlings utter a prolonged loud rasping rattle that can be heard at
some distance whenever disturbed and particularly during feeding.
This call starts and stops abruptly, and if one bird starts, its nestmates
are quick to join in. This 'disturbance' call ( Fischer, 1958) is normally
restricted to feeding and associated activities and excitement once the
eyes are open. Prior to this the slightest disturbance, whether an ex-
ternal stimulus or merely the sudden activity of one member of the
brood, is apt to trigger several seconds of this calling.

Neither of these swifts foul the nest, The nestlings carefully void
fecal wastes over the nest rim. As other workers have noted, this
often results in large accumulations of trash, particularly the chitinous
remains of their insect food, under the nests. This indigestable chitin
is passed completely through the digestive tract and not regurgitated
in the form of pellets as in some other insectivorous birds.



1967 COLLINS: SWIFTS OF TRINIDAD 295

:,/ % J

./- - i :»ep r J

.. I al '.
,·. . . ~. ..I - i - .1,;mAI

31<*95 6/IMM
. Ilillidyr)illillilliLI".

- -I.#-~;..

V
.

«S -
Figure 13.-Chaetum brachyura Hedglings hanging on wall near nest. Nearby

are the mud nests of the potter wasp, Eumenes calialiculatus.

DEVELOPMENT OF HOMEOTHERMY

Young swifts of both species essentially lack any thermoregulatory
capacity at hatching. When they are not brooded their body tempera-
ture quickly drops to near ambient temperatures ( Figs. 14-15). Body
temperatures as low as 25-27°C were recorded for rutilus; the lowest
body temperature recorded for 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 the body tem-
perature declines very little, even during extended periods of exposure.

Nestlings tested in a cold chamber ( Fig. 2) 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 brachgura
nestlings and 72 tests on 12 rutilus nestlings. The rate at which body
temperature dropped lessened sharply with increasing age ( Fig. 16).
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 nestlings' surface to volume ratio. CUP.



296 BULLETIN FLORIDA STATE MUSEUM VoL 11

40-

BO
DY

 T
EM

PE
RA

TU
RE
 

°C
 

BO
DY

 T
EM

PE
R

AT
U

R
E 

'C 38-

36-34- ~ CHAETURA BRACHYURA

32-

30-

6~46810 1214 /1820 22
AGE I N DAYS

Figure 14.-Body temperature of nestlings of Chaetura brach!/ura when un-
brooded. Vertical lines represent daily range in body temperatures, curve con-
nects daily means. Typical daily range in ambient temperature 26.0-30.5 C.

40-

3/

36-

34-

32-

30-

28- CYPSELOIDES RUTILUS

26

24-

6246s,612 14 16 16 20 22
AGE IN DAYS

Figure 15.-Body temperature of nestlings of Cgpseloides rutilus when un-
brooded. Vertical lines represent daily range in body temperatures, curve connects
daily means. Typical daily range in ambient temperature 21.0-25.0 C.



1967 COLLINS: SWIFTS OF TRINIDAD 297

rutilus seem to have an efficient coat of insulation early in nestling
life in its downlike semiplume covering. In addition its contour plum-
age grows in very rapidiy. Both rutitus and brachyura, however, per=
feet their thermoregulatory capacities at about the same rate and
show little difference in their body weights, and hence surface to
volume ratios, during their first 2 weeks of life. Thus brachyura
evidently must depend upon increased heat production to counteract
the effect of cold. As the ambient temperatures of their nest sites are
usually quite warm, they are only rarely exposed to cold and the need
for increased thermogenesis.
TORPOR

The insect food of swifts may be affected markedly by varying
weather conditions. In 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). Young Apus apus can fast as long as 9 days by utilizing their
stored fat deposits and decreasing their body temperature and metabo-
lism at night ( Koskimies, 1950). Similar reactions have been observed

10- 32

33

DE
CR

EA
SE

 I
N 

BO
DY

 T
EM

P 
(°

6
/5

 M
IN

.) ~ C. BRACHYURA
8-

2I
60 35 8 GRUTILUS

es 2
11

4-

1

eS
0-5 6-It 12-17 18-23

AGE IN DAYS

Figure 16.-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.



298 BULLETIN FLORIDA STATE MUSEUM Vol. 11

in several species of tropical swifts when deprived of food for several
days in captivity ( Howell, 1961; pers. 6bser.). Under natural condi-
tions no healthy adult or nestling of either brachgura or rutilus ex-
hibited 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. Several times nestlings that appeared to be injured
or in an extremely weakened condition had abnormally low body
temperatures, and usually 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 neither brachyura nor rutilus seem to use it in
the normal course of events.

ADULT WEIGHT

A sample of 240 individual weighings showed the average adult
weight of brachgura to be 18.3 grams with a range of 15.5-22.0 grams.
Snow ( 1962 ) reported an average weight of 19.8 grams, but this
value was clearly influenced by the inclusion of one female weighing
30 grams, 8 grams heavier than any other recorded for Ch. brachyura
This value is within the expected weight range of the larger but
extremely similar species, Chaetura chapmani, Hellmayr, to which
perhaps it should be attributed. The average weight of 24 juveniles
of brachgura, captured with 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, well below the minimal weight recorded for any adult.

The average adult weight of rutilus was 20,2 grams and ranged
from 17% to 241/4 grams in a sample of 45 individual weighings. A
slight sexual dimorphism in weight was apparent; 24 males averaged
20.6 grams and ranged from 191/4 to 2214 grams, while 19 females
averaged 19.6 grams with a range of 17% to 241/4 grams. This
difference is significant (P< .02).

Monthly mean weights for both sexes of brachyura varied between
a low of 17.1 grams (Oct. 1964) and a high of 18.7 grams ( Aug. 1964).
Somewhat higher ( 18.9, 19.0 g) daily means were also recorded dur-
ing August 1964. Monthly mean weights of both sexes of C. rutilus
varied from a low of 19.6 grams to a high of 20.7 grams, while daily
sample averages varied from a low of 19.0 to a high of 21.1 grams,
both in October 1964. Eighteen individuals of brachgura and eight of
rutilus weighed on two to four separate occasions varied as little as
44 gram and as much as 21/2 grams between weighings.



1967 COLLINS: SWIFTS OF TRINIDAD 299

These weight variations are explainable in terms of temporal varia-
tions in food ayailability. Gladwin and Nau ( 1964) recorded similar
weight changes in Apus apus in England and correlated sharp de-
creases in body weight with prolonged cold or rainy weather, which
greatly decreases the swifts aerial food supply ( Lack and Owen, 1955).
No marked seasonal change in weight was apparent between April and
November in either brachyura or futilus, as is typical in migrant species
such as 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, information on where and
at what rate it is collected is only fragmentary.

In Trinidad 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 the abundant intermittant showers. 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 watched over longer
periods certain specific feeding patterns become discernible.

Chaetura brachyura is by far the most widely distributed species
in Trinidad and is found at almost all elevations. The only Chaetura
that regularly forages over the savanna areas, it is decidedly more
plentiful there and over the lower parts of the northern range than
over those 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 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 bf 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, rutilus is also commonly observed at higher elevations
including the summit of El Tucuche ( 3,068 feet), whereas Ch.
brachyura is uncommon above 1200 feet. Conversely I have never
observed rutilus over the savanna areas. In addition to feeding at



300 BULLETIN FLORIDA STATE MUSEUM Vol. 11

higher elevations, rutilus and another swift, Panyptila cagennensis
(Gmelin), seem at all elevatiohs to feed farther above the ground
than most species of Chaetum. This tendency was also observed for
rutilus in Trinidad by Snow ( 1962) and in Costa Rica by Slud ( 1964),
and elsewhere for niger by Rathbun ( 1925). As this characteristic
of feeding at higher altitudes was most commonly noted during fine
weather and particularly when. both rutilus and cal/ennensis were
part of mixed flocks containing one or more species of Chaetura, it
may be less diagnostic 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 in Washington Cupse-
Zoides niger makes daily trips of several miles from mountain nesting
sites to lowland feeding areas ( Rathbun, 1925). During the breeding
season both species also make long-range movements of several huh-
dred miles to avoid prolonged adverse weather conditions ( Lack,
1955; Udvardy, 1954). Fischer ( 1958) reports seeing Chaetura pela-
gica in New York foraging over a field about 1/4 mile from the nest
and regularly bringing in Ephemeroptera, presumably collected over
a stream 1/8 mile away. He also saw two color-marked birds foraging
2% and 4 miles, respectively, from their nests.

Weather-influenced differences in feeding attitude have been no-
ticed for Apus apus and CUp. 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 with
mouths open to catch whatever happens to get scooped in, but if
watched closely can be seen to change their f[ight direction to snap
up attractive prey items. Additional 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 that are less characteristic of true aeroplankton ( Lack and
Owen, 1955).

The foraging habits of brachyura and rutilus did not change no-
ticeably from day to day, although both species often descended to
nearly ground level during wet weather to feed on the large flights
of winged reproductive termites. Feeding on this temporary plethora
of food was not confined to the swifts. Many species, ranging in size
from house wrens ( Troglodytes aedon) to caciques ( Psarocolius decu-



1967 COLLINS: SWIFTS OF TRINIDAD 801

manus), also preyed on them. Eisenmann ( 1961) noted a similar
array of birds feeding on termite swarms in Panama.

In Brazil Carvalho ( 1962) observed Ch. brachyura and Ch. spini-
cau(la ( Temminck) "rubbing" against dry twigs and plants in bloom
in search of insects or nest material. Several times I saw somewhat
similar behavior by brachyura in Trinidad. The birds seemed to bank
sharply up and Rutter briefly near the outermost branches of trees
extending above the forest canopy, apparently picking insects or
spiders off the leaves. Fischer ( 1958) noticed similar foraging be-
havior in pelagica and it may well be widespread among the swifts.

Other swifts have also been noted feeding in several less typical
ways. Meikeljohn (1928) reports Apus apus landing on the wall of a
house and gathering spiders under the eaves, and Gilbert ( 1944) saw
them foraging for insects and perhaps nest parasites in old swallow
nests.

The stomach contents of the swifts collected during this study
were mostly masses of partly digested insect remains, difficult to
identify. On the other hand, the food they brought the nestlings was
easily identified and probably was the same food the adults con-
sumed. The adults brought the food to the nests in their throats as
a compact mass of undigested insects partly glued together by saliva.
by manipulating the food from the throat of recently fed nestlings I
collected 21 samples of nestling food, 17 from brachyura and 4 from
rutilus. This method, used earlier by Lack and Owen ( 1955), does
not injure the birds if done carefully, and was not repeated often
enough to disrupt the pattern of normal growth.

These samples varied ( Table 10) from a nearly complete food ball
of 326 insects to only a few remnants of a meal. Eight were homo-
geneous masses of either winged ants or winged reproductive ter-
mites. Heterogeneous samples varied from one or two types of insects
to a mixture of some 40 species representing 6 orders of insects and 9
families of spiders. Daily variation in the food brought in by a single
pair of adults was extensive and usually included both homogeneous
and heterogeneous samples.

Interspecific differences in the type of food collected by these
swifts is hard to assess because of the difficulties encountered in col-
lecting samples from rutilus. Seemingly brachyura utilized a great
variety of food items and rutilus only a few. This difference probably
results from the fortuitous collecting of nearly homogeneous samples
of winged ants and termites from rutilus; possibly more samples would
have shown a diversity of prey items equal to that of brachyura.



302 BULLETIN FLORIDA STATE MUSEUM Vol. 11

TABLE 10. CONTENTS OF FOOD BALLS COLLECTED FROM NESTLINGS OF Chae-
tura brachydra AND Cypseloides rutilus.

Number of
Food item samples in which Number of

it occurred individuals

A. Chaetura brach!/ura
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 84
Theridiidae 1 1
Araneidae 1 8
unidentified 1 21

Coleoptera 6 78

Curculionidae 8 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 8 18

Lema sp. 1 8
Chaetocnema sp. 1 2
Systena sp. 2 2

Unidentified 1 2
Altica sp. 1 2

Platypodidae 8 28
Platt,pus sp. 8 28

Staphylinidae 2 8
Coccinellidae 1 1

Nitidulidae 8 8
Stelidota sp. 21 1
Carpophilus sp 2

Orthoptera 1 1

CONTINUED NEXT PAGE-



1967 COLLINS: SWIFTS OF TRINIDAD 808

TABLE 10 CONTINUED-

Number of
Food item samplesin which Number of

it occurred individuals

Hemiptera 2 10
Saldidae 1 1
Tingidae 1 9

Homoptera 2 16
Membracidae 1 2
Aphidae 1 1
Cicadellidae 1 5

Dettocaphalus flavicosta 1 1
Unidentified 1 4
Delphacidae 2 8

Peregrinus maidus 1 1
Sogata sp. 1 1
unidentified 1 6

-Diptera 12 402

Hymenoptera 16 208
Formicidae 12 128

Camponotus sp. 6 41
Trachymqrmex sp. 2 6
Leptalae elohgata 2 15

unidentified 4 75

Isoptera 4 49
Kalotermitidae 1 1

Calcaritermes nigriceps 1 1
Rhinotermitidae 2 82

Coptotermes testareus 2 82
Termitidae 1 16

Nasutitermes costalis 1 16

B. C!/Pseloides rutilus
Hymenoptera 2 19

Formicidae 2 19
Dorgmyrmex sp. 2 19

unidentified 1 7

Isoptera 2 25
Rhinotermitidae 1 20

Dolichorhinoterines Zongilabius 1 20
Termitidae 1 5

Anoplotermes meridianus 1 2
Anoplotermes sp. 1 8



804 BULLETIN FLORIDA STATE MUSEUM Vol. 11

Homogeneous food samples reported for several other swift species
were in no case typical of the normal dav-to-day diet. These simply
corroborate what has already been observed from the foraging be-
havior. Swifts are quick to feed on any temporarily abundant prey
item such as mayflies (Ephemeroptera) or aphids ( Homoptera:
Aphidae ) in temperate areas or winged ants ( Hymenoptera: Formi-
cidae) or termites ( Isoptera) in the tropics.

Swifts feed not only on many different kinds of insects, but on a
wide range of sizes as well. Even so the sizes of prey items any
species of swift takes seem to have certain limits. The upper limit
probably depends upon the size of the bird and what it can com-
fortably swallow.

All food items of brachyura and 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 to be the best available indication of total size. All fractional
measurements were read to the next whole millimeter. The range of
sizes and abundance of each size food item is shown in Fig. 17. As
was true for the prey species diversity, brachyura appears to feed on
a wider range of prey items than rutilus. Again it seems likely that
this seeming difference is an artifact of the sampling. If only the

280

260·

[3 CHAETURA BRACHYURA
140-

~ CYPSELOIDES RUTILUS

120-

too-

NU
M

BE
R 

O
F 

PR
EY

 I
TE

M
S

80-

60- m'.''

·· =r 1 I

40- '5
20- ···

081
01 2345678 9 10

PREY SIZE IN MM

Figure 17.-Size of prey selected by Chaetura brachgura and Cypseloides
rutitus. Diagonal shaded areas represent the portion of the sample consisting
of winged ants and termites.



1967 COLLINS: SWIFTS OF TRINIDAD 805

similar food items ( winged ants and termites) of the two swift species
are compared (Fig. 17), 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 differences in size of these food items the swifts selected may
indicate a similar absence of difference in size of other food items
selected. If so, rutilus and 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 plentiful. During rainy or cold weather fewer insects of all sizes
are available, 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 swifts such as Apus apus may occa-
sionally select food items larger than any taken by either brachyura
or rutilus and rarely take prey as small as some these smaller swifts
take regularly. Similarly, 276 food items collected by another large
swift, Cypseloides niger, in Veracruz, Mexico, ranged from 2-12 mm
in length, with the most frequent sizes selected being 9 and 10 mm,
or about the maximum size recorded for either brach!/ura or 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 C Shelley) sup-
port this idea. These two swifts are nearly equal in size and select
similar sized prey items ( G. E. Watson, pers. comm.).

FEEDING OF YOUNG

The feeding of the nestlings was seen on several occasions but
never at close enough range 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, inserts its bill into the nest-
ling's mouth, and passes the food to it ( see Am-Willi, 1960; Plate
22-23). Food items are often brought to the nest glued together with
saliva into a compact wad or "food ball". Very young birds generally
receive only part of a food ball, 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 brachyura is similar to that of other species
of Chaetura for which there is information. The intervals between



806 BULLETIN FLORIDA STATE MUSEUM Vol. 11

visits of adults to the nest range from 2.5-45 minutes and average
20.5 minutes.

Like other swifts of its genus, Cypseloides rutilus is characteris-
tically absent from the nest for extended periods of time, particularly
after brooding has ended. The feeding intervals of rutirus appears
to be long and irregular. 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 could not be de-
termined.

Smith ( 1928) reports the best studied species of Cypseloides, Cyp.
niger, may leave the nest at dawn and not return to feed the nestling
until nearly dusk. Some feedings have been observed in the morning
hours and indicate higher feeding rates at certain times, possibly
when the nestling is very young. Michael ( 1927) watched an adult
of this species feed the nestling, brood it, and then regurgitate a sec-
ond meal for the young swift several hours after the initial feeding.
Two adults collected at nighttime 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 a#inis in Kenya
( Moreau, 1942b). This swift fed the young birds at intervals ranging
from less than 8 up 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
inlarger 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 time. Both Fischer ( 1958) and Sherman ( 1952) found that
pelagica brought smaller quantities of food per trip during such visits,
occasionally only a single insect.

An increase in feeding rate with increasing age of the nestlings
is indicated in some swifts ( Kendeigh, 1952: 97-98) . This is partic-
ularly true in times of good weather and abundant food, when the
young swifts tend to build up large reserves of subcutaneous fat.
Lack ( 1956c) reports the adults tended to stay away from the nest
longer when the young were well fed and consequently did not beg
as enthusiastically when adults returned with food.



1967 COLLINS: SWIFTS OF TRINIDAD 807

ADULT BEHAVIOR

Flocking.-Both brachyum and Futilus are· most frequently ob-
served flying in company with other swifts of either the same species
or in mixed Rocks of several species. Flocks made up of but one spe-
cies are less characteristic and have been observed for brachyura only
in savanna areas and for rutilus only in the vicinity of the summit of
El Tucuche ( elevation 3,075 ft.), one of the two highest peaks in
Trinidad ( Snow, 1962; pers. obs.). Although at times these Hocks
seemed to be primarily socially oriented, with individuals gliding in
lazy circles and occasionally executing steep dives, they most often
appeared to be loose aggregations of actively feeding birds. I have
observed both single-species and mixed-species flocks during all parts
of the year.

Roosting.-During the breeding season adults of both brachyura
and rutitus roost on or very near their nests. In brachyura, other
adults of the same species were sometimes found in the same man-
hole site with a nesting pair, but roosting at some distance from the
nest. Adults and their late stage young out of the nest usually roosted
in a single tight clump near the nest.

After the breeding season individuals of both species tended to
unite in communal roosting flocks. In brach[/ura these postbreeding
roosting flocks were sometimes as small as 6-10 birds, perhaps repre-
senting but one or two family groups, occasionally as large as 375
birds. The manhole a roosting flock selected changed from year to
year and was not dependent on its having been used as a nest site
that year. Frequently several roosting flocks, both large and small,
occupied manholes less than 50 yards apart on the same night. Post-
breeding roosting flocks of brachgura often included from 1-6 in-
dividuals of Chaetura chapmani ( Fig. 18), an uncommon resident in
Trinidad ( Collins, MS.), and twice one or two individuals of Chaetura
spinicauda ( Snow, 1962; pers. obs.).

In Trinidad the post-breeding roosting flocks of rutilus were usu-
ally only small groups of 2-6 birds, and some pairs continued to roost
apart at their nest site ( Fig. 19). In Mexico Rowley ( 1966: 131)
observed large roosting Rocks of this species, one of which he esti-
mated to contain 300 birds. No other species of swift has been re-
corded roosting with rutilus.

In both species as the breeding season approaches these roosting
flocks tend to break up and the various pairs spend the night adja-
cent to their prospective nest sites. Further information is needed on



808 BULLETIN FLORIDA STATE MUSEUM Vol. 11

6

I f

e
2 S

1,*f

Figure 18.-Roosting Rock of Chaetura brachyura in manhole nest site,
Waller Field, Trinidad. One individual of Chaetum chapmani, with the light
throat, can be seen at the top center,

the exact timing and sequence of this dispersal of the breeding pairs.
Display and copulation.-Owing to the difficulty of observing any

individual f[ying swift for more than a few moments, the display be-
havior of swifts is very poorly known. Like other members of its
genus, brachyura was often seen flying in pairs or trios in the vicinity
of the nesting sites. Though it was never possible to determine the
sexes of the birds involved, this type of display is generally assumed
to be associated with pair formation ( Fischer, 1958). The "V-ing"
display commonly noted in pelagica was not observed during this
study.

Copulation in pelagica has been observed only when adults were



1967 COLLINS: SWIFTS OF TRINIDAD 309

I.

.. 2 7- -3-
.  / f...4

.

-

6 44.4_.tr  -
. , I.

1

ize.V .... 7. 9 +Lit34/0*#-

/*

./. & -™ 18,2, 11 . iEBa
Figure 19.-Roosting pair of C!/Pseloides rutilus on nest, Arima Valley,

Trinidad.

roosting at the nest site ( Fischer, 1958), but for other species it has
also been observed frequently while the birds were in flight ( Dupond,
1943; Smith, 1950; Lack, 1956c; Rowley and Orr, 1962). Twice I saw
two brachyura tumble downward end over end while clinging together,
separate a few feet above the ground, and fly away in different direc-
tions. Similar actions have been noted in Ch. pelagica (pers. obs.)
and Aeronautes saxatilis (Bent, 1940). Two such pairs of saxatilis
collected each proved to be male and female in full breeding condi-
tion ( Bradbury, 1918).

A wing-clattering or wing-clapping threat display at the nest or
roost has been recorded for several species of Chaetura. In its usual
form, as Fischer ( 1958) describes it in pelagica, the bird slowly raises
its wings above its back, leaps backward into flight, and snaps or claps
its wings together three to six times before landing near its original
starting point. The wing-clapping display of brachyura is noticeably



810 BULLETIN FLORIDA STATE MUSEUM Vol. 11

different from that of pelagica and chapmani ( Collins, MS) but sim-
ilar to that of andrei ( Sick, 1959), in which the wings are raised in the
same fashion but the feet usually do not leave the wall and the clap-
ping is confined to a single downward clap, seemingly more against
the wall of the roost than against the opposite wing.

This sort of threat display was not shown by rutilus when sim-
ilarly disturbed at its roost sites, nor was any aerial display or copula-
tory behavior by it noted during this study.

MOLT

Both brachuura and rutilus have a single complete annual molt
which follows the breeding season. Some birds, particularly those
raising second broods, were found in the early stages of this molt
while they still had eggs or young in the nest. Molting birds were ob-
served from August to early December.

In general the molt pattern is similar in both brachyura and rutilus
and in agreement with the sequence Snow ( 1962) outlined for Chae-
tura species. 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 4th or 5th primary. Body molt begins soon
after the start of the primary molt and spans the whole duration of
the molt 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.

Juvenal birds do not molt either remiges or rectrices their Brst
fall. Some light body molt observed in these birds in late September
and October may represent a partial postjuvenal molt of the body
feathers.

PARASITES AND PREDATORS

Ectoparasites in the form of mites ( Acarina) and feather lice
( Mallophaga) were collected from both species. Mallophaga were
abundant on nestlings when their feathers were first emerging from
the sheath, and their eggs were clustered on the dorsal feathers of the
head and neck. Mites were noticed only on the remiges, mainly
on the vanes of the outer primaries. Although these collections have
not yet been identified, the mallophagan species Dennyus brevicapitis
has been reported from brachyura in Trinidad, and Dennyus brunne-



1967 COLLINS: SWIFTS OF TRINIDAD 811

itorques and Eureum uepezi from rutilus in other parts of its range
( Carriker, 1954, 1958).

One specimen of a Rea, Polygenia dunni, was caught on a young
nestling 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. Beebe ( 1950) watched a
pair of nesting Bat Falcons in Venezuela preying heavily on the
smaller swifts, including both brachyura and rutilus.

DISCUSSION

In their general biology Chaetura brachyum and Cypseloides
rutilus appear similar to most swifts for which information is avail-
able. They are almost exclusively aerial in their activities and feed
on airborne 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 adjusted their reproduc-
tive cycles so that they breed when suitable food is most plentiful.
For the swallows, as for the swifts, the breeding peak and the maximal
abundance of food both occur early in the rainy season. For the
nectar feeding hummingbirds and the Bananaquit ( Coereba faveoia),
however, the maximal food abundance and the breeding peak occur
at the height of the dry season ( December-May) when many forest
trees and vines are in flower ( Snow and Snow, 1964 ). The absence
of a pronounced peak in food abundance may permit an extended
breeding season as in two species of thrushes ( Snow and Snow, 1963).
Beyond the tropics, a similar adaptive relationship often exists be-
tween breeding season and maximal food abundance. It can be seen
in a great variety of bird species including both temperate zone tits
of the genus Parus and arctic sandpipers of the genus Calidris ( Gibb,
1954; Holmes, 1966). Previously the explanation of this synchroniza-
tion was that "breeding seasons are adapted to the environmental
cycle in such a way as to secure that the maximum supply of appro-
priate food will be available when the young are hatched and for a
sufficient time after they are first on the wing" ( Thompson, 1950: 179).
More recent studies have shown that another important factor in-



812 BULLETIN FLORIDA STATE MUSEUM Vol. 11

Ruencing the timing of breeding is "the female's obtaining enough
food to form eggs" ( Lack, 1966; 273).

The pattern of nestling growth in both species is typical of altricial
birds, although greatly prolonged in comparison to the several small
passerines Maher ( 1964) reviews. Snow ( 1962) suggests that nest
inaccessibility has allowed a relaxation of selection for the accelerated
growth of nestlings so typical of most passerine birds nesting in the
open.

Chaetura brach!/ura 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, feed-
ing habits, and general behavior only minor specific differences exist.
For the most part these result from the timing of events during de-
velopment. This general similarity is shown by an array of species
that inhabit the area from temperate North America south to sub-
equatorial South America including both sedentary and migratory
species.

An equal degree of similarity exists between Cypseloides rutitus
and other congeneric species, although the little information available
relates mainly to niger.

Although both species studied show similarities to various con-
geners, several pronounced intergeneric differences are manifest in
their reproductive activities. The nest site of rutilus is colder and
darker than that of brachyura, less accessible to predators, and suffers
fewer losses of both eggs and nestlings. At the same time this en-
vironment imposes several hardships on the development of the young.
At hatching the young swift's capaeity for temperature regulation is
poorly developed, and it improves rather slowly during the first weeks
of nestling life. If left unbrooded in the cold environment of the nest,
rutilus nestlings rapidly lose heat to the environment, and much of
the energy available for growth is expended in wasteful thermogenesis.
To prevent such energy-draining heat loss, the adults brood the nest-
lings until their capacity for thermoregulation reaches a stage where
the heat lost without brooding will no longer slow growth and de-
velopment appreciably. In rutilus and its congeners thermoregulation
is aided by the early appearance of an insulating feather coat. This in-
cludes 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 rutilus and other species of Cypseloides to



1967 COLLINS: SWIFTS OF TRINIDAD 818

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 tem-
perate and tropical swifts have shown these birds to be similarly
food limited and their clutch size adapted to the number of young
that can be raised under average conditions ( Lack and Lack, 1951;
Lack and Am, 1947; Lack, 1966; Perrins, 1964; Moreau, 1941, 1942a,
1942b). The same factors doubtless regulate clutch size in other swifts
in both temperate and tropical parts of the New World.

As shown above, the clutch size of brachyura resembles that of
other species of Chaetura and is nearly double the clutch size of
Cypseloides rutilus. Thus rutilus in Trinidad seems capable of ob-
taining food enough to nourish only two young, while brachyura can
gather nearly double that amount. As noted earlier the feeding ranges
of these two swifts overlap only partially, with rutilus feeding at
higher elevations and higher altitudes. Even so, it is hard to accept
the corollary that the food decreases in abundance by nearly 50 per
cent with such shifts in feeding ecology, and hence is entirely re-
sponsible for the reduced clutch size in rutilus. It is equally hard to
accept that rutilus is only half as efBcient at gathering food as brach-
yura. However rutilus has to brood the young longer and more con-
tinuously than brachyura to contend with the colder environment of
its nest site, which reduces the nestlings' food by restricting the forag-
ing to 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.

In other species of Cypseloides a clutch size of two is typical
except in niger, which nests in extremely cold environments at high
elevations in the temperate zone, where it has to contend with an
even less dependable food supply because of prolonged periods 6f
bad weather in its breeding area. Like other swifts facing similar con-
ditions it shows a further reduction in clutch size, namely to a single
egg. It would be interesting to know what size clutch this bird lays
in less rigorous environments in Central America and the West Indies.

Snow ( 1962) suggests that the small size of rutilus nests provides
room for only two nestlings with consequent selection for a clutch of
only two. This seems doubtful unless a maximum nest size for Cypse-



814 BULLETIN FLORIDA STATE MUSEUM Vol. 11

loides can be demonstrated, which seems unlikely in view of the fact
that CDpseloides semicollaris builds no nest and lays only two eggs
( Rowley and Orr, 1962).

In feeding both brach!/ura and rutilus apparently select food items
within the same size ranges, but forage in slightly different areas. This
may well represent an efficient mechanism to avoid interspecific com-
petition 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 differ-
ences in the food items selected may be enough to avoid interspecific
food competition. In support of this hypothesis it would be interest-
ing to know the size prey ranges selected by an extremely large species
such as Cypseloides semicollaris or zonaris and any of the tiny species
of Collocalia or Micropanyptila furcata Sutton.

Feeding at higher altitudes by one species may further reduce
interspecific competition within a given foraging range. Cypseloides
mtilus and Panyptila cayennensis exhibit this habit in Trinidad, and
Collocalia maxima Hume reduces possible interspecific competition
with the several other sympatric species of Conocatia by similarly
foraging at higher altitudes and specializing on the larger higher-flying
insects in Malaysia ( Medway, 1962a). Additional studies will un-
doubtably further clarify the ecological and behavioral differences
existing between sympatric species of aerial foraging insectivorous
birds.

LrrERATURE CITED

Amadon, Dean
1936. Chimney swifts nesting in a barn. Auk, 58: 216-217.

Am-Willi, Hans
1960. Biologische Studien am Alpensegler.

Verlag Vogt-Schild, Solothurn. 205 pp.
Baldwin, Paul H., and William F. Hunter

1968. 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, Ceo. A., Thomas R. Howell, and Tom J. Cade

1957. Torpidity in the white-throated swift, anna hummingbird, and poor-
will. 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.

Zoologica, 35:69-86.



1967 COLLINS: SWIFTS OF TRINIDAD 815

1952. Introducti6n to the ecology of the Arima Valley, Trinidad, B. W. L
Zoolbgica, 37: 157-188.

Belcher, Charles, and G. D. Smooker
1986. Birds of the colony of Trinidad and Tobago. Part III. Ibis p. 26.

Bendire, Charles E.
1895. Life histories of North American birds. U.S. Nat. Mus., Speciai Bull.

No. 3.177-188.
Bent, Arthur C.

1940. Life histories of North American cuckoos, goatsuckers, hummingbirds
and their allies. Bull. U. S. Nat. Mus., 176: 1-506.

Bradbury, William C.
1918. Notes on the nesting habits of the white-throated swift in Colorado.

Condor, 20: 103-110.
Brandt, John H.

1966. Nesting notes on the Collocalia of Micronesia and penninsular Thailand.
Oologists' Record, 40:61-68.

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.,
103:583-549.

1958. Anew species and subspecies of Mallophagan from Venezuela. Acta
Biol. Venezuela, 2: 171-177.

Carvalho, Cory T. de
1961. Notas sobre Chaetum em Belem, Para ( Aves, Apodidae). Rev. Brasil.

Biol., 21: 175-178. ( also published in Dusenia, 1963, 8:105-108).
Coffey, Lula C.

1958. Weights of some chimney swifts at Memphis. Bird-Banding, 29:98-104.
CoIIins, Charles T.

1968, The "downy" nestling plumage of swifts of the genus Cypseloides.
Condor, 65: 824-328.

1965. The down-like nestling plumage of the palm swift Cypsiums parous
( Lichtenstein). Ostrich, 86: 201-202.

1967a. Mist-netting neotropical swifts.
EBBA News, 30:78-75.

1967b. Partial albinism in the chestnut-collared swift in Trinidad. Bull. Brit.
Orn. Club, 87: 122-128.

1967c. On a subterranean nest site of the short-tailed swift in Trinidad.
Oologists' Record, 41: 54-55.

1968. Notes on the biology of Chapman's swift, Chaetura chapmani. (Aves;
Apodidae). Am. Mus. Novitates, in press.

Dabbene, Roberto
1918. Nidos y huevos de vencejos. El Hornero, 1: 198.

Dawson, William R., and Francis C. Evans
1957. Relation of growth and development to temperature regulation in

nestling field and chipping sparrows. Physiol. Zool., 80:315-827.



316 BULLETIN FLORIDA STATE MUSEUM Vol. 11

1960. Relation of growth and development to temperature regulation in
nestling vesper sparrows. Condor, 62:329-840.

Dexter, Ralph W.
1952. Extraparental cooperation in the nesting of chimney swifts. Wilson

Bull., 64:183-189.
Dickinson, J. C., Jr.

1951. A nest of Chactui a vauxi 1ichmondi in central Honduras. Wilson Bull.,
63:201-202.

Dupond, Ch.
1943. L'accouplement des martinets noirs, Apus a. apus (L.). Le Gerfaut,

88:60-62.
Eisenmann, Eugene

1961. Favorite foods of neotropical birds: flying termites and Cecropia cat-
kins. Auk, 78:636-638.

Eisenmann, Eugene, and F. Carlos Lehmann
1962. A new species of swift of the genus Cvpseloides from Colombia. Am.

Mus. Novitates, No. 2117: 1-16.
Fischer, Richard B.

1958. The breeding biology of the chimney swift, Chaetura pelagica ( Lin-
naeus). N.Y. State Mus. and Sci. Serv., Bull., 868:1-141.

Gibb, John
1954. The breeding biology of the great and blue titmice. Ibis, 92:507-539.

Gilbert, M. V.
1944. Swifts scavenging in house-martin's nests. Brit. Birds, 28:185.

Gilliard, E. Thomas
1959. Notes on some birds of northern Venezuela. Am, Mus. Novitates, No.

1927:1-83.
Gladwin, T. W., and B. S. Nau

1964. A study of swift weights. Brit. Birds, 58:844-356.
Griscom, Ludlow

1932. The distribution of bird-life in Guatemala. Bull. Am. Mus. Nat. Hist.,
64: 1-439,

Harwin, R. M.
1960. Notes on the horus swift. Ostrich, 81: 20-24.

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 ( Catidris alpina) in northern Alaska. Condor, 68:8-46.

Holt, E. G.
1927-1928. An ornithological survey of the Serro do Itatiaya, Brazil. Bull. Am.

Mus. Nat. Hist., 57:251-826.
Howell, Thomas R.

1961. An early reference to torpidity in a tropical swift. Condor, 68:505.
Hunter, William F., and Paul H. Baldwin

1962. Nesting of the black swift in Montana. Wilson Bull. 74:409-416.



1967 COLLINS: SWIFTS OF TRINIDAD 817

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, 60:78-84.

1961. Salivary glands in the black swift. Condor, 63:338.
Kahl, M. Philip, Jr.

1962. Bioenergetics of growth in nestling wood storks. Condor, 64: 169-188.
Kendeigh, S. Charles

1952. Parental care and its evolution in birds. Illinois Biol. Monographs,
22:1-856.

Knorr, Owen A.
1961. The geographical and ecological distribution of the black swift in

Colorado. Wilson Bull., 78: 155-170.
1962. Black swift breeds in Utah. Condor, 64:79.

Koskimies, Jukka
1950. The life 6f 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, 78: 1-82.
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. 289 pp.
1966. Population Studies on Birds. Clarendon Press, Oxford. 841 pp

Lack, David, and Hans Arn
1947. Die Bedeutung der Gelegegr6sse beim AIpensegler. Orinth. Beob., 44: -

188-210.
Lack, David, and Elizabeth Lack

1951. The breeding biology of the swift, Apus apus. Ibis, 98: 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: 120-186.

Legg, Ken
1956. A sea-cave nest of the black swift. Condor, 58: 188-187.

Lowery, George H., Jr. and Walter W. Dalquest
1951. Birds from the state of Veracruz, Mexico. Univ. Kansas Publ. Mus. Nat.

Hist., 8.581-649.
Maher, William J.

1964. Growth rate and development of endothermy in the snow bunting
(Plectrophenax niualis) and lapland longspur ( Calcarius lapponicus)
at Barrow, Alaska. Ecology, 45: 520-528.

Marshall, A. J., and H. J. deS. Disney
1956. Photostimulation of an equatorial bird ( Que?ea qudea, Linnaeus).

Nature, 177: 148-144.



318 BULLETIN FLORIDA STATE MUSEUM Vol. 11

Marshall, A. J., and S. J. Folley
1956. The origin of nest cement in edible-nest swiftlets ( Collocalia spp.)

Proc. Zool. Soc. London, 126:883-889.
Medway, Lord

1961. The identity of Collocatia fuciphaga C Thunburg). Ibis, 108: 625-626.
1962a. The swiftlets ( Collocatia) of the Niah Cave, Sarawak. Part I, Breeding

biology. Ibis, 104: 45-66.
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 CoUocalia maxima Hume. Proc.
Zool. Soc. Lond., 188:305-315.

1966. Field characters as a guide to the specific relations of swifts. Proc. Linn.
Soc. Lond., 177:151-172.

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
1938. A young black swift. Condor, 85:80.

Miller, Alden H.
1959. Response to experimental light increments by Andean sparrows from an

equatorial area. Condor, 61: 844-347.
Moreau, R. E.

1941. A contribution to the breeding biology of the palm swift, Cypselus par-
-UUS. Journ. East Africa Uganda Nat. Hist. Soc., 15: 154-170.

1942a. The breeding biology of Micropus caller streubelii Hartlaub, the white-
rumped swift. Ibis, 1942: 27-49.

1942b. Colletoptera allinis at the nest. Ostrich, 13:187-147.
Orton, J.

1871. Notes on some birds in the museum of Vassar College. Am. Nat., 4:711-
717.

Parkes, Kenneth C., and George A. Clark, Jr.
1964. Additional records of avian egg teeth. Wilson Bull., 76: 147-158.

Perrins, Christopher
1964. Survival of young swifts in relation to brood size. Nature, 201: 1147-

1148.
Peters, James L.

1940. Check-list of Birds of the World. Vol. 4. Harvard University Press,
Cambridge. 291 pp.

Rathbun, S. F.
1925. The black swift and its habits. Auk, 42:497-516.

Rowley, J. Stuart
1966. Breeding birds of the Sierra Madre del Sur, Oaxaca, Mexico. Proc.

Western Foundation Vert. Zool., 1: 107-204.
Rowley, J. Stuart, and Robert T. Orr

1962. The nesting of the white-naped swift. Condor, 64: 861-367.



1967 COLLINS: SWIFTS OF TRINIDAD 319

1965. Nesting and feeding habits of the white-collared swift. Condor, 67: -
449-456.

Schmidt, Rudolf K.
1965.  Brutbiologie des Weissburzelseglers Apus caller cafer ( Lichtenstein)

auf der Kaphalbinsel. Journ. f. Ornith. 106:295-806.
Sherman, Althea R.

1952. Birds of an Iowa Dooryard. The Christopher Pub. House, Boston.
270 PP.

Sick, H.
1948a. The nest of Chaetura andrei meridionalis. Auk., 65: 515-520.
1948b. The nesting of Reinarda squamata ( Cassin). Auk., 65: 169-174.
1959. Notes on the biology of two Brazilian swifts, Chaetura andrei and

Chaetura cinereiventris. Auk., 76:471-477.
Sims, R. W.

1961. The identification of Malaysian species of swiftlets Conocalia. Ibis,
108a:205-210.

Skutch, Alexander F.
1961. Helpers among birds. Condor, 68: 198-226.
1964. Life histories of hermit hummingbirds. Auk., 81:5-25.

Slud, Paul
1964. The birds of Costa Rica. Bull. Am. Mus. Nat. Hist., 128: 1-480.

Smith, Emily
1928. Black swifts nest behind a waterfall. Condor, 30:186-138.

Snow, David W.
1962. Notes on the biology of Trinidad swifts. Zoologica, 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. Zoologica,

49:1-89.
Steyn, Peter

1966. The occurrence of the horus swift, Apus horus ( Heuglin), at Paarl,
Cape Province. Ostrich, 37:192-198.

Sutton, George M.
1948. Breeding of Richmond's swift in Venezuela. Wilson Bull., 60: 189-190.

Thompson, A. Landsborough
1950. Factors determining the breeding seasons of birds: an introductory

review. Ibis, 92: 178-184.
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 cross-

bill. Condor, 67:416-422.
Udvardy, Miklos D. F.

1954. Summer movements of black swifts in relation to weather conditions.
Condor, 56: 261-267.



820 BULLETIN FLORIDA STATE MUSEUM Vol. 11

Weitnauer, Emil
1947. Am Neste des Mauerseglers, Apus apus apus (L)  Ornith. Beob.,

44:133-182.
Zimmer, John T.

1953. Studies of Peruvian birds. No. 64, The Swifts: family Apodidae. Am.
Mus. Novitates, No. 1690: 1-20.



Contributions to the-'BuLLETIN of  THE 'FLORiDA STATE MUSEUM may be in any
fidld  bf; bidogy. Manu*trifts_dealift¥ *ikh, natural history Or„sydematic prdblems
ih,>61*ing the sbytheast*rn United Status .ot the 'Caribbead a*a are soliBitad
gspecially.

Manuscripts should Ibe of medium length--50 to ,200 pages. Examination fo;
suitability is made by an Editorial Board.

The BULLETIN is distributed w6rldwide thro~igh institutional subscriptions and
excliange5 only. It is 66nsidBred Ithe :tespousibility  of the aut}ior to distribute his
paper, td all interebted individuals. To aid in, tbi#, ffty 660185 irre f~irnished the
author without cost.

PREPARATION OF MANUSCRIPT -

Highly rec6mmended as a guide is the volume:

Co~ference' of Biological Editors, Committee on Form and Style.
1960. Style manual for biological journals.

Amer. Inst. Biol. Sci., Washington. 92 p.

Manuscripts should be typewritten with double spacing throughout, with ample
margins, and on only one side of. the: paper. The author should keep a copy; the
original and a carbon must be submitted. Tables and legends of figures should
be typed on sheets separate from. the text. Several legdnds 6r tables may be
placed on a single sheet.

Illustrations, including maps and photographs, should be referred to as "figures."
All ·illustratiOns are Yeduced to a maximum 6f 4-1/4 by 7-1/8 inches. Size scales,
wherever they are necessary, should be incorporated into the figure.

References t6 literature should conform with the bibliographic style used in recent -
numbers of the BULLETIN. Spell 6ut in full the titles of non-English serials and
places of publication.

Footnote material should be kept to a minimum. H6wever, provide copy for a
footnote detailing the title; afAliations, and address of the author (see recent
numbers 6f the BULLETIN~.

Manuscripts must be accompanied by a synopsis-a brief and factual summary
(not a mere description) of the contents and conclusions, which points out the
presence of any new information and indicates its relevance: In it list all new
organjsms described and give their ranges; indicate all tax6nomic changes pro-
posed. The synopsis, written in full sentences, should be concise, but completely
intelligible in itself without references to the paper, thereby enabling the busy
reader to decide more surely than he can from the, title alone whether the paper
merits his reading. The synopsis will be published with the paper. It does not
replace the usual conclusions or summary sections. It may also serve as copy
for the abstracting services.

Manuscripts and all editorial matters should be addressed to:

Managing Editor of the BULLETIN
Florida State Museum
Seagle Building
Gainesville, Florida