The common swift (Apus apus) is a medium-sized bird, superficially similar to the barn swallow or house martin but somewhat larger. It is, however, completely unrelated to those passerine species, since swifts are in the separate order Apodiformes. The resemblances between the groups are due to convergent evolution reflecting similar life styles. Swifts’ nearest relatives are thought to be the New World hummingbirds and the Southeast Asian treeswifts.
Common swifts are 16–17 cm long with a wingspan of 38–40 cmand entirely blackish-brown except for a small white or pale grey patch on their chins which is not visible from a distance. They have a short forked tail and very long swept-back wings that resemble a crescent or a boomerang.