Published by the 
Wilson Ornithological Society
OBSERVATIONS ON THE BREEDING BIOLOGY OF THE SILKY-
TAILED NIGHTJAR (CAPRIMULGUS SERICOCAUDATUS MENGELI)
FIONA A. WILKINSON1
OBSERVATIONS ON THE BREEDING BIOLOGY OF THE SILKY-
TAILED NIGHTJAR (CAPRIMULGUS SERICOCAUDATUS MENGELI)
FIONA A. WILKINSON1
ABSTRACT.?I found 15 nests of the Silky-tailed Nightjar (Caprimulgus sericocaudatus mengeli) from 1994 to 2004 at
Cocha Cashu Biological Station, Manu National Park, Peru?. Females and males shared incubation and brooding duties with
females on the nest during the day and males on at night. Nest relief occurred between 0300?0600 and 1800?2100 hrs.
Two-egg clutches were placed on bare ground or on leaf-litter in more mature strands of forest. The semi-precocial young
were mobile within 24 hrs of hatching and remained in the area with an adult through the fledgling stage. Both males and
females feigned injury during incubation and brooding if disturbed. Three nesting sites were used for 5 years and another
for 10 years, suggesting strong site fidelity and possibly a strong pair bond among long-lived individuals. Received 29
August 2005. Accepted 29 January 2009.
The behavior and ecology of most nightjars and
nighthawks (Family Caprimulgidae) are poorly
known resulting from their largely crepuscular
and nocturnal habits. They are difficult to locate
and monitor, especially in complex habitats (e.g.,
rainforests) and only limited data about their
breeding biology are available.
The Silky-tailed Nightjar (Caprimulgus serico-
caudatus) is one of 12 neotropical nightjars which
breeds in South America and belongs to the
largest and most cosmopolitan genus, Caprimul-
gus (Cleere 1998, Holyoak 2001). Adult males
and females of the 12 species have been
described; however, the young of nine species
remain unknown (Cleere 1998, Holyoak 2001).
The Silky-tailed Nightjar is one of the least
studied members of the genus and current
literature is limited to descriptions based on a
few museum specimens (Cleere 1998, Holyoak
2001) and range extensions via vocalizations
(Madron?o N and Esquivel 1997, Alexio et al.
2000).
The known range of this species extends from
eastern Peru? and Bolivia across Paraguay and
southeastern Brazil into northern Argentina
(Cleere 1998, Holyoak 2001). Two subspecies
(C. s. sericocaudatus, C. s. mengeli) are recog-
nized and differ in size (Dickerman 1975),
vocalizations (Hardy and Straneck 1989), and
geographic range. C. s. mengeli, is slightly smaller
and darker than the nominate race (Dickerman
1975), and is only known from the Amazonian
Basin, whereas C. s. sericocaudatus is restricted to
the Atlantic Forest region of South America
(Cleere 1998, Holyoak 2001). I found nests of
C. s. mengeli in the vicinity of Manu National
Park in southeastern Peru?. Species identification
was confirmed via vocalizations and plumage
characteristics, and I use Silky-tailed Nightjar to
refer to the mengeli subspecies. The objectives of
this study were to describe (1) aspects of the
breeding biology of Silky-tailed Nightjars, and (2)
associated behaviors.
METHODS
Study Area.?Field work was conducted be-
tween September and November in 1994, 1995,
1997?1999, and 2004 at Cocha Cashu Biological
Station (CCBS) (11u 549 S, 77u 229 W, elevation
,380 m), Manu National Park, Department of
Madre de Dios, Peru?. A network of trails
surrounding the research station encompasses
,12 km2 of undisturbed lowland floodplain and
evergreen tropical forest (Terborgh et al. 1984).
The trails are relatively close together (,100?
400 m) forming forest ??blocks?? surrounding an
oxbow lake (Cocha Cashu; Fig. 1). Another
oxbow lake (Cocha Totora) borders the trail
system to the east. Habitats within the study area
were divided using Trail # 12 that is east-west
between the two lakes, and which separates
mature, high canopy forest to the north and
younger forest to the south (J. W. Terborgh, pers.
comm.). There are swamps throughout the study
area, but most are in the southern portion.
Ambient temperature ranged from 10 to 33u C
from August to December with a mean of 24u C.
Rainfall was concentrated during November to
May with an annual total of ,2,000 mm (Ter-
borgh 1990).
Nightjar activity (e.g., calling, nest relief,
feeding young) typically began 15 to 30 min
1 U.S. Geological Survey, Patuxent Wildlife Research
Center, National Museum of Natural History, Smithsonian
Institution, P. O. Box 37012, Washington, D.C. 20013,
USA; e-mail: wilkinsf@si.edu
The Wilson Journal of Ornithology 121(3):498?505, 2009
498
prior to sunset and sunrise during the breeding
season and lasted from 2 to 60 min, depending on
nesting stage (incubation, brooding). Censuses
and nest observations occurred from 0300 to 0600
and 1700 to 2100 hrs.
Censuses.?I found several Silky-tailed Night-
jar nests between September and November 1994
and 1995 while searching for nests of Ocellated
Poorwills (Nyctiphrynus ocellatus), which exhib-
ited a strong preference for areas along the trails
(FAW, unpubl. data). Six census routes (x? 5
4.14 km, range 5 1.5?6.6 km in length) were
established in 1997 covering an area of ,5 km2.
Routes were selected based on areas where nests
were located and calls were heard most frequently
in 1994 and 1995 for both species. Calling
nightjars could be heard at least 100 m from
trails. Censuses were conducted by walking the
trails during selected hours 2?3 times per week
per time period. Areas where birds were flushed
and/or heard calling outside of the census
parameters were visited the following dawn or
dusk to check for nightjar activity (nests, calls,
etc.) and were sporadically checked throughout
the field season.
I detected the birds? orangish red eye shine with
a headlamp or a hand-held spotlight during dark
periods. Birds nested on the ground and tended to
align themselves parallel to the trail; it was
necessary to walk trails in both directions to
detect eye shine. Nightjars do not build an actual
nest structure and I define a ??nest?? as the location
of the eggs or nestlings.
Birds were captured by approaching the nest
silently and covering them with a hand-held insect
net. I attempted to capture adults within 12 to
24 hrs of nest discovery but only made 1?2
attempts per field season to minimize the
possibility of nest abandonment. Eggs, nestlings,
and adults were weighed using a Pesola spring
balance and measurements were taken with
calipers. Eggs were handled with a spoon to
FIG. 1. Nests, sites, and calling activity of Silky-tailed Nightjars at Cocha Cashu Biological Station, Manu National
Park, Peru?, 1994?1999 and 2004. Solid symbols 5 nests, open symbols 5 calling individuals, s 5 nesting site, f 5 adult
males that flushed during the day, and * 5 two individual birds calling at the same time from approximately the
same location.
Wilkinson N BREEDING BIOLOGY OF THE SILKY-TAILED NIGHTJAR 499?   1994   ?   1995    *   1996 
996   ? 1999 
Trail System 
Trails Censused 
prevent transfer of human scent and numbered
with waterproof ink. I measured right wing chord,
tail length, bill length from nostril to tip, length of
the right tarsus plus middle toe, and length of the
longest right rictal bristle of adults and nestlings.
Adults were banded with a color band on each leg
and gender was assigned based on plumage
characteristics. Males have a prominent white
collar and the tips of the outer tail feathers are
white; the white is replaced by buff in females
(Cleere 1998, Holyoak 2001).
Observations.?Nests were initially monitored
within 12 to 24 hrs of discovery and revisited every
3 days alternating between morning and evening
hours until the nest was no longer located. One nest
with young was observed on two different
occasions outside regular observation periods to
assess diurnal and nocturnal activities.
Observations were made using 10 3 42
binoculars and/or a Sony Hi-8 video camera from
a blind 10 m from the nest. The video camera,
coupled with an infrared illuminator, allowed me
to observe and record birds in complete darkness.
I analyzed 127 min of video footage of nesting
behaviors. All nests were checked twice a week
outside of the main observation periods during the
day and night to verify which adult was on the
nest. The nesting adult and nest were observed
until the adult returned, if flushed, and resumed
nesting duties or for 20 min, after which I left the
area to minimize risk of predation and/or
abandonment.
Locations of all calling individuals and nests
were plotted on a map to estimate population
density and site fidelity between years. These
points were also used to create a fixed shape to
estimate core area use (ha) by breeding pairs and I
refer to this area as a nesting site. The elliptical
shape was based on site # 3 where a concentration
of nightjar activity was recorded for five field
seasons, including two nests found in 1998. This
shape was centered on each nest site in each year
to examine the frequency of use of the surround-
ing areas between years. The combined areas were
considered to be a single site if there was 25% or
more overlap.
Habitat Measurements.?I measured habitat
characteristics after young fledged, or when nests
were abandoned or depredated, using a modified
version of James and Schugart?s (1970) method of
vegetation analysis. Two circular plots (A and B)
centered on the original nest site (n 5 9) were
created to measure ground and canopy cover, and
numbers of plants within plot A (1-m diam) were
counted in each of three height categories (0.0?
0.5, .0.5?1.0, and .1.0?1.5 m). Two perpendic-
ular 10-m transects were established in plot B (10-
m diam) with the first in the direction of the bird.
The number of woody shrubs and saplings
(#7.5 cm in diameter at breast height [DBH])
for 5 m behind and in front of the nest at arms
width (,2 m) was counted along this transect.
Ground and canopy cover at 1-m intervals (n 5
21) were measured along the two transects. The
number of trees, including palms, with DBH
$10 cm within plot B was recorded. The same
parameters were measured at 20 randomly
selected (using a random numbers table [Heyer
et al. 1994]) nest sites (10 in each of the northern
and southern portions of the study area). Transects
at these sites were north-south and east-west. I
tested for homogeneity of variances (F test) for
habitat characteristics and compared means with
either a two-sample Student?s t-test (equal vari-
ances) or Welch?s t-test (unequal variances).
PAST Version 1.81 (Hammer et al. 2001) was
used for all analyses and significance was set at
0.05. Means 6 SD are presented.
RESULTS
I captured, measured, and banded four adults.
Only mass of females (x? 5 75.25 6 1.0 g, n 5 2)
differed from males (x? 5 69.75 6 1.0 g, n 5 2).
Ten nests were observed for 73 hrs, 37:15 hrs
during incubation and 35:45 hrs during brooding.
Breeding Biology and Behavior.?I found 15
nests between 1994 and 2004. Fourteen were
within 5 m of a trail; the other was in an open area
25 m from the nearest trail. Twelve nests
contained two eggs, one had one egg and a
newly hatched chick, and one had two nestlings
.1-week of age. The contents of one nest were
unknown, although the injury-feigning behavior
of the female indicated the presence of nestlings
(Table 1). Nests were on the ground either on bare
patches or on leaf-litter.
Eggs were elliptical, smooth, and pale pinkish-
orange in color with dark maroon specks concen-
trated at the blunt end. Color intensity and
concentration of specks varied among eggs. Eggs
averaged 27.1 6 2.1 mm in length (range 5 21.8?
31.0 mm, n 5 22) by 21.4 6 3.1 mm in width
(range 5 18.0?30.7 mm), and had a mass of 6.68
6 1.2 g (range 5 4.0?8.5 g).
The precise duration of the incubation and
brooding periods could not be calculated because
500 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 121, No. 3, September 2009
all nests were active (with eggs or nestlings) when
located. The earliest and latest nests with eggs
were on 16 September 1998 and 25 October 1994,
respectively. A nest found on 21 September 1998
contained nestlings estimated to be ,14 days of
age based on size and plumage, suggesting a
laying date of ,20 August.
Both adults incubated and brooded young.
Females were on the nest during the day at all
times. The earliest and latest times a female was
observed on a nest during incubation and
brooding were 0503 and 1900, and 0328 and
2000 hrs, respectively. Males were only observed
incubating or brooding at night. The earliest and
latest times a male was on a nest during
incubation were 1831 and 0440 hrs and, during
brooding, 2030 and 0540 hrs.
Chicks were semi-precocial, hatched on suc-
cessive days, covered with golden down, weighed
6?7 g (n 5 2), and were mobile within 24 hrs.
Dark brown pin feathers began to appear by day 3.
Nestlings could ??hop?? over short distances (x?
distance 5 2.7 6 2.84 m, range 5 0.7?6.0 m, n 5
3) by 3 days of age and up to 3.6 6 0.8 m (range
5 3.0?5.0 m, n 5 6) at 4/5 days. Nestlings were
capable of flying ,6 m by 11 and 12 days of age,
and were active during the day. They often
emerged from under the female to preen, stretch
their wings, and peck at decaying material near
the nest. The sheaths of the alar feathers were
broken at this stage, displaying brown tips and
coverts were grayish brown with distinguishable
brown circular markings. Pin feathers along the
capital and caudal tracts continued to develop
making the nestlings more cryptic. The light
colored tips of the outer tail feathers were visible
in flight. Nestlings at nest # 10 flushed from the
same area in the early morning every few days
until about 24 days of age; an adult was present at
times.
Eight of 13 nests with eggs were depredated
(Table 1), but only after the nests had been
abandoned. Seven of eight failed nests were
depredated within 12 hrs of the adult not returning
after flushing in response to natural disturbance or
a capture attempt. The female from the eighth nest
consistently flushed whenever there was move-
ment nearby. She flushed at day 9, and did not
TABLE 1. Site fidelity and nesting activity of Silky-tailed Nightjars at Cocha Cashu Biological Station, Manu National
Park, Peru? (e 5 egg, n 5 nestling, f 5 fledgling, d 5 depredated, and u 5 egg pipped but hatching not successful).
Site # Year Nest # Activity Beginning status Ending status
1 1994 1 Nest 2e 2f
1995 4 Nest/calls 2nc 2f
1997 Callsa
1998 9 Nest/calls 2e 2d
2 1994 2 Nest 2e 2d
3 1995 3 Nest/callsa 2e 2d
1996 Nestb
1997 7 Nest/callsa 2e 2d
1998 8 Nest/callsa 2e 2d
1998 12 Nest/callsa 2e 2d
2004 Calls
4 1995 5 Nest/calls 2e 1u, 1f
1998 Calls
1999 Calls
5 1997 6 Nest/calls 2e 2d
1998 Callsa
6 1995 Callsa
1998 10 Nest 2n 2f
1999 14 Nest/calls 2e 2f
7 1998 11 Nest/calls 2e 2d
8 1997 Calls
1999 13 Nest/calls 1e, 1n 2f
9 2004 15 Nest 2e ?
10 1998 Callsa
a Two individuals calling.
b Nest located in alternate year.
c Assumed 2 nestlings based on behavior.
Wilkinson N BREEDING BIOLOGY OF THE SILKY-TAILED NIGHTJAR 501
return; the eggs disappeared 1 week later.
Presumably, 11 young from six nests fledged
successfully. One other egg pipped but hatching
was unsuccessful and the fate of nest # 15 was
uncertain as the female was incubating when I left
the study area. I recorded no instances of
predation on adults or chicks.
Nesting adults faced parallel to the trail and
tended to flush when I approached within 10 m
(range 5 1?10 m, n 5 11) or if an intruder
remained stationary near the nest for 5?10 min.
Incubating females, when flushed, typically flew
5?20 m to an open area on the ground (usually the
trail) or a branch (2?10 m high), positioning
themselves perpendicular to it. Regardless of
where the female flushed, she remained still or
drooped one wing and quietly flapped it, or
flapped both wings several times prior to flying
behind nearby vegetation. Females resumed the
same position as prior flushing upon returning to
the nest.
Injury-feigning was more intense during the
brooding period. A female at one nest flushed to
the middle of the trail, revealing two newly
hatched nestlings. As I approached the nest, she
quietly but rapidly flapped her wings up and down
against the ground and then flew straight at me
circling around my head within 1 m, before
returning to the trail where she continued flapping
her wings. When I moved toward her, she flew
short distances (2?3 m) from the nest, and
continued to display. The amount of injury-
feigning decreased as the distance from the nest
increased. On two occasions at another nest, when
nestlings were ,3 and then 6 days of age, the
male flushed and flew 5 m to an open area in the
trail. He then vigorously flapped his wings hard
against the ground before flying while calling
several times. Brooding adults, after being
flushed, would settle within 1?1.5 m of the nest
and call to the young by making short, guttural
sounds. Nestlings would either approach the adult
with short hops prior to burrowing underneath or
would hop to a new location and wait for the adult
to join them. Adults returned to the young within
10?30 min.
Nest relief occurred just prior to daybreak
(0300?0600 hrs) or in complete darkness at night
(1800?2100 hrs). The nesting adult during incu-
bation typically bobbed its head up and down
while looking from side to side, and quietly flew
straight up from the eggs as the mate approached.
The mate quietly flew to the vicinity, looked
around and, at times, rolled the eggs prior to
settling on the nest. I heard an adult Silky-tailed
Nightjar calling at nest # 6 in the early evening
near the incubating female for about 14 min
(1756?1809 hrs) and, following the last call, this
adult, presumably the male, flew over my head to
a nearby area. The female then rocked back and
forth and looked around for the next 40 min. She
flushed straight up from the nest at 1900 hrs
making two loud short, sharp clicking sounds that
sounded mechanical rather than vocal.
Twice I heard counter-calling between males
and females at nest sites prior to morning nest
relief (once during incubation and again during
brooding). On a separate occasion, a brooding
male called 16 times from the nest during the
morning and, after feeding the young via
regurgitation, stopped, intently looked around
and then gave a different one-note high pitched
??sweet?? call six times before flying. Almost
immediately, both adults gave this one-note call
three times each.
Individuals called between dusk and dawn
during the breeding season; calling activity was
greatest in October. Calling occurred in the early
evening between 1740 and 2038 hrs, peaking at
,1815 hrs and, in the morning, between 0400 and
0550 hrs peaking at 0453 hrs. Only one or two
calls were usually given. However, on three
separate occasions (twice in Oct 1995, once in
Sep 1999) at site # 6, an adult was heard calling
continuously between 0420 and 0525 hrs for
6 min, 45 min, and 14 min, respectively.
It is uncertain where the mate of the nesting
pair roosts. Two males flushed from the ground
during the day in October 1997 from areas
relatively near active nests (site # 3, 200 m; site
# 5, 275 m). They did not display any distinctive
behaviors (e.g., injury-feigning), but flew low and
parallel to the forest floor, further into the forest
block toward the incubating females.
I found no evidence of double brooding but the
birds likely renested when the first attempt was
unsuccessful. Two nests were found in 1998
within site # 3 at locations 210 m apart, and I
assumed they were from the same breeding pair.
Nest # 8 was located on 16 September and
depredated on 22 September. The following day a
pair of nightjars was heard counter-calling at
0511 hrs about 100 m east of nest # 8; the male
was seen calling from a perch about 5 m above
ground level along the trail?s edge. No other calls
were heard in the vicinity and it is possible the
502 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 121, No. 3, September 2009
male incubating two eggs at nest # 12, 21 days
later, was the one I saw earlier.
Nest Site and Habitat.?I found 14 nests in the
northern section of the study area, including those
along or near Trail # 12 (Fig. 1), while one was in
the southern section. The 15 nests were at nine
different sites, three of which included two or
more nests. The mean distances between nests
within these sites were: 115 m (site # 1, range 5
5?170 m, n 5 3); 140 (site # 3, range 5 5?210 m,
n 5 6); and 125 m (site # 6, n 5 2). A tenth site
was delineated based on calls of two individuals
consistently heard from 8 October to 4 November
1998.
Six sites were used in several years and,
although nests were not located in all years, site
# 8 may have been used for 3 years while sites #?s
1, 4, and 6 may have been used for 5 years
(Table 1). A Silky-tailed Nightjar nest was
located during my absence in 1996 within site #
3 (D. J. Brightsmith, pers. comm.) confirming this
site was used for 4 consecutive years. Calls heard
during the 2004 census suggest that nightjars may
have occupied this area for 10 years. The core
area used at this site was ,5.84 ha. Core area
estimations for sites that overlapped by at least
25% were ,9.33 ha (site # 6) and ,10.60 ha (site
# 1).
Distances between used sites and nearest
neighbors were: 750 m (1994, n 5 1), 450 6
71 m (1995, range 5 400?550 m, n 5 4), 750 6
446 m (1997, range 5 400?1325 m, n 5 4), 418
6 94 m (1998, range 5 325?575, n 5 7), and 550
6 248 m (1999, range 5 375?725 m, n 5 3), and
1600 m (2004, n 5 1).
Only the number of trees with DBH $10 cm
differed significantly between nest and random
sites (Table 2). The average number of trees
within plot B near the northern nest sites (x? 5
9.11 6 6.27, n 5 9) was greater (P 5 0.02) than
number of trees in the northern random sites (x? 5
3.00 6 2.16, n 5 10), and greater (P 5 0.03) than
all random sites combined (x? 5 3.65 6 2.37, n 5
20). There was no significant difference between
canopy and ground cover among all sites;
however, 80% of nests (n 5 12) were .20 m
from areas that periodically flooded (low areas
consisting of streams or small swamps). The
remaining three were within 15 m of small,
depressed areas ,3?10 m in length dominated
by small patches of broadleaf monocots including
Heliconia sp. (Family Heliconiaceae) and Reneal-
mia sp. (Family Zingiberaceae).
DISCUSSION
An August to December breeding period for the
Silky-tailed Nightjar coincides with the latter half
of the dry season through the beginning of the
rainy season. This is similar to the breeding period
for the Ocellated Poorwill (FAW, unpubl. data)
and for Blackish Nightjars (Caprimulgus nigres-
cens) in western Brazil (Roth 1985).
Adult nightjars have been documented to share
incubation and brooding duties with the female
attending the nest during the day and the male at
night (Jackson 1985, Hustler and Mitchell 1997).
The Silky-tailed Nightjar followed this pattern but
these observations contrast to those for Blackish
(Roth 1985) and Puerto Rican (C. noctitherus;
Vilella 1995) nightjars where males were most
frequently observed incubating and brooding
during the day.
Young nightjars are mobile and able to move
short distances within 24 hrs of hatching (Raynor
1941, Ingels et al. 1984). Their mobility increases
and young are capable of flying short distances as
they became older. European Nightjars (C.
europaeus) can fly up to 16 m by 18 days of
age (Lack 1957). Nightjars may leave the nesting
area (Roth 1985) at about this age, or remain near
the nest site with or without adults (Longstaff and
Jourdain 1926). The young at nest # 10 regularly
flushed from the same site, but remained within
the area until 24 days of age. They were not
located thereafter and it is possible they either
fledged or still occupied the area. Young Europe-
an Nightjars have been reported to occupy their
nest site until 45?46 days of age with both adults
nearby (Tutt 1955).
Nightjars eat a variety of insects and young are
fed by their parents via regurgitation (Raynor
1941, Cleere 1998). Nestlings may also forage
for ground insects around the nest-site (Vilella
1995) or pick up small soil granules to aid in
digestion (Jenkinson and Mengel 1970). This was
most likely the case for the young I observed
pecking at decaying material, a behavior also
observed for young Puerto Rican Nightjars (Vilella
1995), Ocellated Poorwills (FAW, unpubl. data),
and adult Whip-poor-wills (C. vociferous; Jones
1933).
The sharp clicking sounds made by the female
at nest # 11 may have been produced by wing-
clapping or other mechanical means associated
with being disturbed prior to nest relief. There
isn?t a particular behavior associated with these
Wilkinson N BREEDING BIOLOGY OF THE SILKY-TAILED NIGHTJAR 503
noises but similar sounds have been reported for
several caprimulgid species while in flight (Sick
1993), when disturbed from rest (Coward 1928),
while defending territories (Mengel et al. 1972),
during display flights (Hilty and Brown 1986,
Clay et. al. 2000), and courtship (Lack 1932,
Mengel et al. 1972).
Injury-feigning is a common anti-predator
behavior used by caprimulgids during nesting
and intensity of the display varies by gender and
nesting stage. Exaggerated injury-feigning has
been reported for male Swamp Nightjars (C.
natalensis) during incubation (Hustler and Mitch-
ell 1997) and for brooding Freckled Nightjars (C.
tristigma; Steyn 1971) with more intense displays
at night. I observed similar intensity displayed by
a brooding male Silky-tailed Nightjar in contrast
to Lack?s (1932) observation that this behavior is
poorly developed and less intense during the
night.
Both males and females readily flushed from
nests when approached. Adults are extremely
cryptic but eggs are relatively conspicuous. Nest
success may be negatively correlated with adults?
flushing behavior during incubation, length of
time they were away from the nest, and age of the
eggs. Adults repositioned themselves when they
returned to the nest after being flushed, facing the
same way and parallel to the trail. The direction
birds faced was towards open areas which
potentially provided a larger area to escape from
predators.
Nightjars re-use nest sites between years (Berry
1979, Jackson 1985, Vilella 1995). Repeated use
of certain areas at CCBS indicates Silky-tailed
Nightjars exhibit site fidelity. Nests within sites
#?s 1, 3, and 6 were within 5?170 m of one
another in different years. The two nests in site # 1
were 170 m apart (1994?1995); 3 years later a
nest was found directly across the trail (5 m) from
the nest in 1994. Nests of banded pairs of
Ocellated Poorwills were 0 to 140 m apart
between years (FAW, unpubl. data).
Nightjar density, territory size, and home range
cannot be accurately measured without marking
and radio-tracking individuals. However, an
estimate of 8.59 ha (n 5 3, range 5 5.84?
10.60 ha) indicates breeding pairs occupy a
relatively large area. This estimate is larger than
those reported for areas of primary use (e.g.,
territory, home range) for Puerto Rican Nightjars
(5.2 ha; Villella 1995), Fiery-necked Nightjars (C.
pectoralis) (5.8 ha; Jackson 1985), and five
species (6.5 ha) in Zimbabwe (Jackson 1984),
but within the range for European Nightjars
(5.87?25.20 ha; Lack 1932, Berry 1979, Cadbury
1981).
Use of nest sites in areas with increased
numbers of large trees (DBH $10 cm) may
indicate a preference for older forest, which
corresponds to areas less likely to flood. Birds at
CCBS appeared to nest away from areas com-
monly inundated, perhaps to prevent flooding of
nests during heavy rains. The closed canopy in
these areas also makes for a more open understory
which may facilitate feeding. Ocellated Poorwills,
the most common nightjar species at CCBS, in
contrast nested close to swampy areas, primarily
south of Trail # 12 (FAW, unpubl. data). Both
species used Trail # 12 every year of the study and
TABLE 2. Habitat characteristics (mean 6 SD) of nest sites of Silky-tailed Nightjars (STNJ) (n 5 9) and random sites
in both the northern (n 5 10) and southern (n 5 10) sections of the study area at Cocha Cashu Biological Station, Manu
Park, Peru?, 1994?1999 and 2004.
Variable STNJ Northern Southern
Plot A, 1-m diam
Seedlings, 0?0.5 m 6.44 6 2.65 3.9 6 2.81 4.4 6 3.41
Seedlings, .0.5?1.0 m 0.89 6 1.69 0.10 6 0.31 0.20 6 0.42
Seedlings, .1.0?1.5 m 0.44 6 1.01 0.20 6 0.63 0.20 6 0.42
Canopy cover, % 100 100 90 6 31.62
Ground cover, % 0 30 6 48.30 10 6 31.62
Plot B, 10-m diam
Woody stems, #7.5 cm in front 2.89 6 3.26
Woody stems, #7.5 cm behind 3.56 6 2.40
Trees, $10 cm dbh 9.11 6 6.27 3.00 6 2.16 4.3 6 2.50
Canopy cover, % 95 6 7.53 98 6 6.02 83 6 23.25
Ground cover, % 45 6 23.22 32 6 15.23 35 6 17.25
504 THE WILSON JOURNAL OF ORNITHOLOGY N Vol. 121, No. 3, September 2009
I have no evidence suggesting conflict for space,
food, or other resources.
ACKNOWLEDGMENTS
This project was made possible by the support and
encouragement of M. S. Foster. M. U. Valdez, P. J.
Murphy, Wilfredo Arizabal, Ariadne Angulo, M. S.
Foster, P. S. Wenninger, Carolina Pickens, D. J. Bright-
smith, C. J. Paciorek, and M. D. Huama?n contributed to
the census data and nest observations. N. K. Johnson
provided egg data and J. T. Marshall helped with the
initial sonograms. I am grateful to J. W. Terborgh, the
Instituto Nacional de Recursos Naturales of the Peruvian
Ministry of Agriculture (INRENA), and the administration
of Manu National Park for permission to conduct the
research at Cocha Cashu Biological Station. My appreci-
ation is also extended to F. J. Vilella, M. K. Robbins, J. A.
Sedgewick, J. A. Smallwood, M. S. Foster, C. E. Braun,
and an anonymous reviewer for their critical reviews of
this manuscript.
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