Swifts. The shape of the swallow's nest is elongated, which is a type of swiftlet, because the swiftlet is a species of the genus White-bellied Swiftlet in the family Arnidae, and elongated swallow's nests are often used for swiftlet breeding. Swiftlets have a wide distribution range, mainly in tropical, subtropical and temperate regions in Southeast Asia, South Asia and the Western Pacific. In addition, elongated nests are also popular because their shape is convenient for swiftlet breeding.