Description ebird

Distinctive small swallow with blue-black upperparts, a very large white rump patch, and snow-white underparts. Juvenile in late summer and autumn is duller above and dingier below than adult. Very similar to Asian House-Martin, but note white rump patch extending further up back, brighter white underparts, and slightly larger size. Compare also with other swallows and House Swift; note the relatively shallowly forked and streamerless tail, fluttery flight, and clean white underparts. In west of range, overlaps with very similar Western House-Martin (formerly treated as one species); note present species’ significantly larger rump patch. Breeds colonially, frequently building mud nests under the eaves of buildings; forages over varied open and semi-open habitats, especially water bodies and adjacent fields. Gives a soft burbling trill.