The Plain swift (Apus unicolor), is a species of medium-sized swift in the Apodidae family. Although this bird is superficially similar to a barn swallow or the common house martin, it is not related to those passerine species. The resemblances between the groups are due to convergent evolution reflecting similar life styles. Swifts have very short legs that they use only for clinging to vertical surfaces. They never settle voluntarily on the ground, and spend most of their lives in the air, feeding on insects that they catch in their beaks. They drink on the wing.