Delichon is a small genus of passerine birds that belongs to the swallow family and contains three species named as house martins. These are chunky, bull-headed and short-tailed birds, blackish-blue above with a contrasting white rump, and with white or grey underparts. They have feathering on the toes and tarsi that is characteristic of this genus. The house martins are closely related to other swallows that build mud nests, particularly the "Hirundo" barn swallows. They breed only in Europe, Asia and the mountains of North Africa. Two species, the common and Asian house martins, migrate south in winter, while the Nepal house martin is resident in the Himalayas year-round.