Swift Bird is a remarkably well-adapted bird, with an almost entirely aerial life. Swift Bird is uniformly dark brown with a whitish throat, although often appears black at long range or in poor light. It has a slender cigarlike body with a short forked tail, a short rounded head and very long and narrow sickle-shaped wings that are almost entirely 'hand', the 'elbow' or carpal joint lying very close to the body. They fly strongly, the narrow wings appearing to flicker in rapid flight, although for most of the time they glide or soar, even sleeping on the wing, which they achieve by shutting down the brain one hemisphere at a time.
Swift Bird is found over virtually all and every habitat, the choice dictated only by the abundance of flying insects. Swifts can often be seen feeding low over water bodies in poor weather, conditions in which aquatic insects are more likely to emerge than terrestrial ones. Large weather systems are avoided, the swifts leaving the area completely, but in fine weather they use all available airspace. Formerly adapted to nesting in crevices in cliffs or even in trees, in modern times they nest in urban areas, favouring older houses and churches and using roof eaves, wall cavities and any available crack or crevice in a building.
During the breeding season Swift Birds are quite vocal, particularly in the evenings when nesting birds will perform a group screaming display, racing around their loose colony in a fast-moving flock, sometimes joined by other birds calling from within their nests. Non-breeders will also do this when gathering prior to ascending to higher altitudes for aerial roosting. The calls are high-pitched shrill trilling sounds, varying in pitch and tempo, such as "rrrheeeiiii...", "ssrrriiii...", "zrrreeee..." or "iiiiirrrrrreeeeee...", sometimes begun more slowly with hoarse stuttering sounds.