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Observations on the breeding biology of the Silky-tailed Nightjar (Caprimulgus sericocaudatus mengeli).

Article Excerpt
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 sericocaudatus) is one of 12 neotropical nightjars which breeds in South America and belongs to the largest and most cosmopolitan genus, Caprimulgus (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 (Madrono N and Esquivel 1997, Alexio et al. 2000).

The known range of this species extends from eastern Peril and Bolivia across Paraguay and southeastern Brazil into northern Argentina (Cleere 1998, Holyoak 2001). Two subspecies (C. s. sericocaudatus, C. s. mengeli) are recognized 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 Perf. 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 between September and November in 1994, 1995, 1997-1999, and 2004 at Cocha Cashu Biological Station (CCBS) (11[degrees] 54' S, 77[degrees] 22' W, elevation ~380 m), Manu National Park, Department of Madre de Dios, Peru. A network of trails surrounding the research station encompasses ~12 [km.sup.2] of undisturbed lowland floodplain and evergreen tropical forest (Terborgh et al. 1984). The trails are relatively close together (~100400 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 33[degrees]C from August to December with a mean of 24[degrees]C. Rainfall was concentrated during November to May with an annual total of ~2,000 mm (Terborgh 1990).

Nightjar activity (e.g., calling, nest relief, feeding young) typically began 15 to 30 min 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.

[FIGURE 1 OMITTED]

Censuses.--I found several Silky-tailed Nightjar nests between September and November 1994 and 1995 while searching for nests of Ocellated Poorwills (Nyctiphrynus ocellatus), which exhibited a strong preference for areas along the trails (FAW, unpubl, data). Six census routes ([bar.x] = 4.14 km, range = 1.5-6.6 km in length) were established in 1997 covering an area of ~5 [km.sup.2]. 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 prevent transfer of human scent and numbered with waterproof ink. I measured fight wing chord, tail length, bill length from nostril to tip, length of the right tarsus plus middle toe, and length of the longest fight rictal bristle of adults and nestlings. Adults were banded with a color band on each leg and...

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