A small dark Aerodramus swiftlet that is nearly impossible to distinguish from closely-related species such as Mossy-nest and White-nest Swiftlets. Dark above and paler gray below; rump varies from dirty white to dark depending on subspecies. Tail averages more squared-off and less prominently forked than White-nest and Germain’s swiftlets, but best identified when on feather-and-saliva nests, which are dark, as the name suggests. Nests in large colonies in caves, often with other species of swiftlet. Chitters at nest, but usually fairly quiet.