swift, common name for small, swallowlike birds related to the hummingbird and found all over the world, chiefly in the tropics. They range in size from 6 to 12 in. (15–30 cm) in length. Swifts have long wings and small feet and can perch only on vertical surfaces. They scoop up insects in their wide mouths while on the wing. Swifts are the most rapid fliers known among living creatures. In the United States the common eastern species is the chimney swift, Chaetura pelagica, miscalled chimney swallow. Its spiny tail acts as a prop when it clings to the chimneys in which it builds its nest of twigs, cemented with saliva. In the W United States are the black, Vaux's, and white-throated swifts. Some Asian swifts make their entire nest of a salivary secretion; these are the nests that are used to make bird's-nest soup. The common European swift is sometimes called hawk swallow. Other species include the brown-throated spinetail swift ( C. gigantea ) of India and the Philippines; the scissor-tailed swift ( Panyptila sancti-Hieronymi ) of Guatemala; the white-rumped swift ( Apus caffer ) of Africa; and the palm swift ( Cypsiurus parvus ) of SE Asia. True swifts vary greatly in their nesting habits, some being cliff breeders, some using palm leaves for building their nests, and others nesting in chimneys. Found in a separate family of the same order are the crested swifts, which are restricted to SE Asia. These birds roost in trees and inhabit the open woodlands. They feed on insects, caught on the wing. Crested swifts build tiny nests, about the size of a silver dollar, on tree branches. They deposit a single gray-blue egg, which is glued to the center of the nest. Swifts are classified in the phylum Chordata, subphylum Vertebrata, class Aves, order Apodiformes, families Apodidae (swifts) and Hemiprocnidae (crested swifts).