Hirundinidae (swallows, martins, hirundines; class Aves, order Passeriformes)
A family of small, brown, dark-blue, or dark-green birds, many with white under-parts, which have short bills with a broad gape, long and pointed wings, and a medium to long tail which is often strongly forked. The legs are short, and feathered in some species. Hirundines inhabit open areas and are aerial insectivores. They nest in cavities in trees and rocks, in burrows, or (e.g. Hirundo rustica
, the swallow or barn swallow) in mud nests on ledges and buildings. Delichon urbica
(house martin), one of the three species in its genus, is particularly associated with human habitations. Sand martins (four species of Riparia
) nest in tunnels in banks. There are 17–19 genera in the family, with 77–81 species, found world-wide, many of them migratory.