A distinctive small hirundine with glossy blue-black upperparts, a bold white rump, and clean white underparts. Juveniles seen in late summer and autumn appear duller above and more off-white below. Compared with other swallows, it shows a shallower forked tail without long streamers and has a more fluttering, slightly jerky flight. In the eastern part of its range it overlaps with the very similar Siberian House-Martin; this species can be told by its noticeably smaller white rump patch. It breeds in colonies, often attaching mud nests beneath building eaves, and feeds over a variety of open and semi-open areas, especially around water and nearby fields. Its call is a soft, burbling trill

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