Endemic to West Mexico, White-naped Swift is large and completely dark, save for a striking white hindcollar, which is rarely visible from below. A fairly common resident from 1500-3000 m, White-naped Swift is found primarily in arid highlands, but it is far-ranging and often wanders into humid coastal lowlands. Its flight is quick and powerful, with relatively slow wingbeats. It may soar for extended periods without flapping. It has a square tipped (or slightly concave) tail, notably less forked than that of the similar White-collared Swift (Streptoprocne zonaris), and its vocalizations - loud chatters and shrieks - generally are deeper than those of White-collared. While adult White-collared swifts are easily distinguished by their namesake collar, juveniles of that species may lack them and appear all dark from below. Streptoprocne swifts nest colonially in caves (especially of limestone), sinkholes, and similar structures, often in the vicinity of waterfalls. The gap in the geographic range of White-naped Swift may be explained by a lack of such suitable habitat.