A medium-sized swift with long tail-streamers that give it a different shape than any other swift. Adult has a dark greenish-blue crest visible while it perches, mostly on trees. It has uniform pale gray upperparts, black lores with a fine white border above, and much rufous on the face of the male. Underwing feathers, breast, and flanks are pale gray, and belly is whitish. Female has a dark mask on the eye, replacing the male’s rufous coloration. The species is partial to lightly wooded country, avoiding open plains and wet forests. Mostly seen on the wing, and at times perched, making a characteristic “gek-kuk” call.