Description
Swifts are the most aerial of birds. Larger species are amongst the fastest fliers in the animal kingdom, with the White-throated Needletail having been reported flying at up to 169 km/h (105 mph). Even the Common Swift can cruise at a maximum speed of 31 metres per second (112 km/h, 70 mph). In a single year the common swift can cover at least 200,000 km.
The swiftlets or cave swiftlets have developed a form of echolocation for navigating through dark cave systems where they roost. One species, Aerodramus papuensis, has recently been discovered to use this navigation at night outside its cave roost also.
Swifts occur on all the continents, though not in the far north or large deserts, and on many oceanic islands. Like swallows and martins, the swifts of temperate regions are strongly migratory and winter in the tropics. Some species can survive short periods of cold weather by entering torpor, a state similar to hibernation.
Many have a characteristic shape, with a short forked tail and very long swept-back wings that resemble a crescent or a boomerang. The flight of some species is characterised by a distinctive "flicking" action quite different from swallows. Swifts range in size from the Pygmy Swiftlet (Collocalia troglodytes), which weighs 5.4 g and measures 9 cm (3.7 inches) long, to the Purple Needletail (Hirundapus celebensis), which weighs 184 g (6.5 oz) and measures 25 cm (10 inches) long.
The nest of many species is glued to a vertical surface with saliva, and the genus Aerodramus use only that substance, which is the basis for bird's nest soup. The eggs hatch after 19 to 23 days, and the young leave the nest after a further six to eight weeks. Both parents assist in raising the young.
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