Swift?

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For other meanings of the word Swift see Swift (other meanings).
The swifts are birds superficially similar to swallows but are completely unrelated to those passerine species; swifts are in the separate order Apodiformes, which they formerly shared with the hummingbirds.
The resemblances between the 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 Greek ?????, apous, meaning “without feet”, since swifts have very short legs and never settle voluntarily on the ground, perching instead on vertical surfaces. The tradition of depicting swifts without feet continued into the Middle Ages, as see in the heraldic martlet.
Swifts are the most aerial of birds and some, like the Common Swift, even sleep and mate on the wing. One group, the Swiftlets or Cave Swiftlets have developed a form of echolocation for navigating through dark cave systems where they roost.
Like swallows and martins, the swifts of temperate regions are strongly migratory and winter in the tropics.
Many swifts 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.
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.