Gray-brown swiftlet with a pale gray rump and a squared-off tail. The westernmost ranging species in the genus and the only member throughout much of its range. Smaller than most other swifts in range except for House Swift, which is black overall with a sharp white rump and throat. Tends to travel in small to medium-sized flocks, often swooping low over bodies of water. Builds dark bowl-shaped nests in closely-clustered colonies under rocky overhangs, in caves, and in old buildings. Gives clicking calls and twitters, especially when near colonies.