A medium-sized swift that appears dark overall, relieved only by a white throat. It is almost always seen on the wing, moving at high speed with firm, stiff wingbeats, and is larger and longer-winged than swallows. Unlike Pacific Swift and other fork-tailed swifts or needletails, it lacks any white rump patch. It nests in crevices in cliffs and buildings and ranges widely over many habitats while hunting flying insects, often above lakes and reservoirs where swallows gather. Typically it flies higher than swallows, except when it dips low to the water to drink, briefly skimming the surface. Its presence is often announced by a piercing, wheezy scream, especially near nesting sites.