Reproductive biology and distribution of the silky-tailed nightjar (Antrostomus sericocaudatus sericocaudatus) in Argentina

Abstract

∙ The Silky-tailed Nightjar (Antrostomus sericocaudatus) is traditionally considered rare, poorly known, and possibly threatened. It comprises two subspecies: A. s. mengeli in the Amazon basin and A. s. sericocaudatus in the Atlantic Forest – a rapidly disappearing biodiversity hotspot in southeastern Brazil, eastern Paraguay, and the province of Misiones in Argentina. The subspecies differ in vocalizations and morphology, but reproductive biology has been studied only for A. s. mengeli. We found A. s. sericocaudatus throughout remaining Atlantic Forest in Misiones, and studied 10 nests. During courtship, the male sang incessantly from a high branch above the future nest site; when the female landed on another branch, he doubled the pace of his song, flew to the female (who emitted soft barks), dropped his wings, fanned his tail, and mounted the female while emitting a low croak. Antrostomus s. sericocaudatus laid two immaculate white eggs, in contrast to A. s. mengeli and most other Antrostomus, which lay eggs with markings. The incubation period was 19 days, and hatchlings were covered in dense pinkish-brown down (vs. “golden” in A. s. mengeli). During the day, incubation and brooding were mostly performed by the female, although the male was found incubating once during the day and brooding once at night. Both parents performed distraction displays from incubation until the chicks were 18–19 days old. Considering the restricted range of A. s. sericocaudatus, its dependence on remaining Atlantic Forest, and its differences with A. s. mengeli, it is important to study its population size, population trajectory, and tolerance of forest fragmentation, in order to determine its global conservation status.