African black swift
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Distinctive features
The African black swift is 16–18 cm (6.3–7.1 in) long and bulky like a pallid swift; it appears entirely blackish-brown except for a small white or pale grey patch on the chin which is not visible from a distance. It has a short forked tail and very long swept-back wings that resemble a crescent or a boomerang. This species is very similar to the common swift but can be distinguished under optimum viewing conditions by the contrast between its black back and paler secondary wing feathers. The heavier build also gives it a distinctive flight action, which consisted of a steady level flight interspersed with short glides.
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Habitat
The breeding habitat is damp mountains, typically between 1,600 and 2,400 m (5,200 and 7,900 ft), and less often at lower altitudes. This species feeds readily over lowland, and can form very large flocks, often with other gregarious swifts.
Movements
The nominate South African subspecies is migratory, wintering further north. Other subspecies are resident. Of the other seven accepted forms, the most widespread is the small and dark A. b. subsp. roehli of east Africa.
Two other dark races, A. b. balstoni and A. b. mayottensis (see: Malagasy black swift), are restricted to Madagascar and the Comoro Islands respectively. It has been suggested that some balstoni migrate to the continental mainland when not breeding, but this has not been proved.
Nesting
East African birds nest in hollow trees, whereas in South Africa this species uses cliffs, usually inland but also on the coast. The African black swift is a colonial breeder, sometimes forming mixed colonies with alpine swifts. The nest is a shallow grass cup glued to the substrate with saliva, and the typical clutch is one or two eggs.
Call
The call is a strident double-rasped, hissing scream zzzzzzzZZZTT, dissimilar to that of its confusion species.