The swifts are a family, Apodidae, of highly aerial birds. They are superficially similar to swallows, but are not closely related to passerine species. Swifts are placed in the order Apodiformes, which they share with hummingbirds. The treeswifts are closely related to the true swifts, but form a separate family, the Hemiprocnidae. Resemblances between swifts and swallows are due to convergent evolution, reflecting similar life styles based on catching insects in flight. The family scientific name comes from the Ancient Greek απους, apous, meaning "without feet", since swifts have very short legs and rarely ever settle voluntarily on the ground, clinging instead to vertical surfaces. The tradition of depicting swifts without feet continued into the Middle Ages, as seen in the heraldic martlet.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[1] (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. Compared with typical birds, swiftlet wings have proportionately large wingtip bones. By changing the angle between the wingtip bones and the forelimb bones, they are able to alter the shape and area of their wings, maximizing their efficiency and maneuverability at various speeds.[3] With the exception from their relatives the hummingbirds, they are also unique among birds in being able to rotate their wings from the base, a trait that allows the wing to remain rigid and fully extended and derive power on both upstroke and downstroke. In other birds, the upstroke is a passive stroke used to lift the wing into position.Swifts occur on all the continents, though not in the far north or large deserts, and on many oceanic islands.[6] 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.[5] 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.Swifts and treeswifts have long been considered to be relatives of the hummingbirds, a judgement corroborated by the discovery of the Jungornithidae, which were apparently swift-like hummingbird relatives, and of primitive hummingbirds such as Eurotrochilus. Traditional taxonomies place the hummingbird family (Trochilidae) in the same order as the swifts and treeswifts (and no other birds); the Sibley-Ahlquist taxonomy treated this group as a superorder in which the swift order was called Trochiliformes.The Apodiformes diversified during the Eocene, at the end of which the extant families were present; fossil genera are known from all over temperate Europe, between today's Denmark and France, such as the primitive Scaniacypselus (Early - Middle Eocene) and the more modern Procypseloides (Late Eocene/Early Oligocene - Early Miocene). A prehistoric genus sometimes assigned to the swifts, Primapus (Early Eocene of England), might also be a more distant ancestor.The taxonomy of the swifts is in general complicated, with genus and species boundaries widely disputed, especially amongst the swiftlets. Analysis of behavior and vocalizations is complicated by common parallel evolution, while analyses of different morphological traits and of various DNA sequences have yielded equivocal and partly contradictory results (Thomassen et al., 2005).(Phys.org) —A combined team of researchers from Bern University and the Swiss Ornithological Institute has found that alpine swifts are able to fly for up to 200 days at a time, without landing. The team learned of the bird's unique abilities to fly for such long stretches by attaching tiny sensors to several migrating specimens. They have published the results of their findings in the journal Nature Communications.

• published: 18 Oct 2013
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