Aerodramus

Aerodramus is a genus of small, dark, cave-nesting birds in the Collocaliini tribe of the swift family. Its members are confined to tropical and subtropical regions in southern Asia, Oceania and northeastern Australia. Many of its members were formerly classified in Collocalia, but were first placed in a separate genus by American ornithologist Harry Church Oberholser in 1906.

This is a taxonomically difficult group of very similar species. Echolocation, DNA sequencing and parasitic lice have all been used to establish relationships, but some problems, such as the placement of the Papuan swiftlet are not fully resolved. These swiftlets can pose major identification problems where several species occur.

What distinguishes Aerodramus swiftlets from other swifts, and indeed almost all other birds, is their ability to use a simple but effective form of echolocation. This enables them to navigate within the breeding and roosting caves.

The nests of Aerodramus swiftlets are constructed with saliva as a major component. In two species, saliva is the only material used, and the nests are collected for the famous Chinese delicacy 'bird's nest soup', the over-collection of which puts pressure on the swiftlet populations.

The range of these swiftlets is confined to tropical southern Asia, Oceania, northeastern Australia and the Indian Ocean, with the greatest diversity in Southeast Asia, Indonesia and Papua New Guinea. Several of the species are restricted to small islands, and their limited range can make them vulnerable, like the Seychelles, Whitehead's and Guam swiftlets. The Mangaia swiftlet is a recently extinct species known only from fossils.

Aerodramus swiftlets are in many respects typical swifts, having narrow wings for fast flight, and a wide gape and small reduced beak surrounded by bristles for catching insects in flight. They have dull plumage which is mainly in shades of black, brown, and grey. Members of this genus typically have dark brown upper wings and upper body, sometimes with a paler rump, light brown underparts, a paler throat, and brownish-white under-wings with dark brown "armpits". Males and female plumages are similar in appearance, as is that of the juvenile, for those species for which it has been described; in some species the juvenile shows pale fringes to the flight feathers.

The legs, as with many swifts, are very short, preventing the birds from perching, but allowing them to cling to vertical surfaces. The flight is mainly gliding due to very long primary feathers and small breast muscles. Aerodramus swiftlets, depending on species, weigh 8–35 grammes (0.28–1.23 oz) and are 9–16 centimetres (0.28–1.23 in) long. These swiftlets are very similar, and where several species occur, such as Borneo, New Guinea and the Philippines, may not be separable in the field.

Aerodramus swiftlets are aerial insectivores, which take prey like flies on the wing. They roost and breed in caves; during the day they leave the caves to forage for food, and return to roost at night. They are monogamous and both partners take part in caring for the nestlings. Males perform aerial displays to attract females and mating occurs at the nest. The breeding season overlaps the wet season, which corresponds to an increased insect population.