Apus pacificus

The Pacific swift (Apus pacificus) is a bird which breeds in eastern Asia. This swift is strongly migratory, spending the northern hemisphere's winter in Southeast Asia and Australia. The general shape and blackish plumage recall its relative, the common swift, from which it is distinguished by a white rump band and heavily marked underparts. The sexes are identical in appearance, although young birds can be identified by pale fringes to the wing feathers that are absent in adults. This swift's main call is a screech typical of its family. It is one of a group of closely related Asian swifts formerly regarded as one species. The Pacific swift is found in a wide range of climatic zones and habitats. It breeds in sheltered locations such as caves, natural rock crevices or under the roofs of houses. The nest is a half-cup of dry grass and other fine material that is gathered in flight, cemented with saliva and attached to a vertical surface. The two or three white eggs are incubated for about seventeen days to hatching. Subsequently, the chicks have a long but variable period in the nest before they are fully fledged. When the parents cannot find sufficient food in bad weather, the young can survive for days without being fed by metabolising body fat. Like all members of its family, the Pacific swift feeds exclusively on insects caught in flight. It tends to hunt higher than most of its relatives other than the white-throated needletail. The Pacific swift has a large population and extensive breeding area, and faces few threats from predators or human activities. It is classed as being of least concern by the International Union for Conservation of Nature. It has occurred as far afield as the US and New Zealand, and it is a very rare vagrant in Europe. The swifts form the bird family Apodidae, which is divided into several genera. The Pacific swift is in the Old World genus Apus, which is characterised by dark, glossy plumage, a forked tail and sharply pointed wings. Until recently, the Pacific swift was considered to have five subspecies, but three have now been elevated to full species status as part of a 'fork-tailed swift' superspecies. The proposed name of the superspecies was formerly a synonym for the Pacific swift. A 2011 study proposed the following treatment. The long-tailed birds from the Tibetan Plateau with a narrow white throat patch are separated as Salim Ali's swift, A. salimali, the small swifts with narrow white rumps from the Himalayas of India, Nepal and Bhutan become Blyth's swift, A. leuconyx, and the population that breeds in limestone caves in northern Southeast Asia, characterised by a green iridescence and shallow tail fork, is split as Cook's swift, A. cooki. The remaining subspecies are the nominate A. p. pacificus and the southern race A. p. kurodae (which includes the Tibetan population formerly named as kanoi). This arrangement has been accepted by the International Ornithological Committee (IOC), but not the International Union for Conservation of Nature. A 2012 paper showed that cooki is closely related to the dark-rumped swift, A. acuticauda, which should therefore be included in the pacificus clade, but made no further taxonomic recommendations. This swift was first described by John Latham in 1801 as Hirundo pacifica. Scopoli separated the swifts from the swallows as the genus Apus in 1777. Apus, like Apodidae, is derived from the Greek απους, apous, meaning 'without feet', a reference to the small, weak legs of these most aerial of birds, and pacificus refers to the Pacific Ocean. At 17–18 cm (6.7–7.1 in) in length, the Pacific swift is the largest of the Apus swifts. It has a 43–54-cm (17–21-in) wingspan. Females are slightly heavier than males, averaging 44.5 g (1.57 oz) against 42.5 g (1.50 oz). It is similar in general shape to the common swift, although slightly longer-winged and with a more protruding head. The fork of the tail is deeper, and the rump is broader. The upperparts are black, apart from a white rump band and a somewhat greyer head. The underparts are black, although white fringes to the feathers gives the belly a scaly appearance when seen well from below. The tail and the upper wings are black, and the underwings are brown. The eyes are brown and the small bill and very short legs are black. The sexes are identically plumaged, and juveniles differ from the adults only in that the feathers show pale fringes, particularly on the wings. The southern subspecies, A. p. kurodae, has a narrower white rump (15 mm/0.6 in against the nominate form's 20 mm/0.8 in), a grey throat and blacker underparts. Juveniles of migratory Apus swifts have a partial moult prior to migration, but retain the larger wing feathers. The moult is completed in the wintering grounds, where adults have a complete moult. This species is usually straightforward to identify. The white-rumped swift is similar to Pacific swift, but its slender body and long, deeply forked tail make it appear quite different from its more powerfully built relative. A possible pitfall is a partially leucistic common swift with a white rump. The Pacific swift can be distinguished with care by its deeper tail fork, longer wings, bigger head, larger white throat patch and patterned underparts. In parts of Southeast Asia, migrating Pacific swifts pass through the resident ranges of former subspecies, and good views are then necessary to be sure of correct identification.