The White-rumped Swift (Apus caffer), is a species of swift that is similar to a house martin, but is completely unrelated to that species. They are native to sub-Saharan Africa, and have expanded into Morocco and southern Spain. The wintering grounds of those that migrate is not well known. Only the tropical African populations are year-round residents.
The White-rumped Swift is 5.5 to 6 inches long and has a short forked tail and long swept-back wings that resemble a boomerang or crescent moon. It is entirely dark except for a pale throat patch and a narrow white rump. It is similar to the closely related Little Swift, but is slimmer, darker and has a more forked tail and a narrower white rump. It is mainly a quiet species, although a twittering trill is sometimes given.
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. This species appropriates the nests of little swifts and those swallows which build retort-shaped nests. The original owners of the nests are driven away, or the white-rumps settle in the nest and refuse to move. Once occupied, the nest is lined with feathers and saliva, and one or two eggs are laid.