Medium-sized swift, dark overall with a white throat. Almost always seen in fast, direct flight, which, as the name suggests, is swift. Bigger and longer-winged than swallows, with strong stiff wingbeats. Lacks the white rump patches of similarly-sized Pacific Swift (and other "fork-tailed swifts") and various needletails. 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. Calls frequently, especially near the nest, giving a high-pitched wheezing scream.