A rare and highly range-restricted dark swift lacking any white on the lower back. Underparts can have a white-fringed appearance, but may sometimes appear uniform due to wear. Note contrast between belly and solid black undertail. Combination of namesake dark rump and dark face distinguishes this species from other similar “fork-tailed swifts.” Breeds in damp forested hills with waterfalls, steep cliffs, and ledges; forages over other habitats as well. Gives high, thin calls, as well as chittery trilling screams.