Huge swift with powerful, falcon-like flight. Overall coloration is gray with a paler throat and mottling on the belly, but often looks blackish when seen in flight overhead. A darker, blackish population nests in Luanda, Angola, and wanders widely. Found over a wide variety of habitats, though often in the vicinity of rock outcroppings. Near breeding colonies, gives an exuberant trilled call. Similar in size and shape to Alpine Swift, but separated by the dark rather than white belly. Separated from all other swifts by large size.