Almost always seen in flight, which, as the name suggests, is swift. Nests in cavities in cliffs and buildings. Ranges widely over any habitat in search of aerial insects, often over lakes and reservoirs where swallows congregate. Usually flies higher than swallows except when swooping low to drink by splashing briefly on water surface. Bigger and longer-winged than swallows, with dark plumage, strong stiff wingbeats, faster and more direct flight. Lacks the white rump patches of similarly-sized Pacific Swift (and other "fork-tailed swifts") and various needletails.