Delichon is a small group of birds in the swallow family, known as house martins. It includes four species that are chunky, bull-headed, and short-tailed. They have dark blue feathers on their backs, a white rump, and white or grey underparts. Unique to this group, they have feathers on their toes and legs. House martins are closely related to other swallows that build mud nests, especially the Hirundo barn swallows. They breed in Europe, Asia, and the mountains of North Africa. The common, Siberian, and Asian house martins migrate south for the winter, while the Nepal house martin stays in the Himalayas all year.
House martins build nests in groups on cliffs or buildings, using mud lined with feathers or grass. They usually lay two or three white eggs. Both parents work together to build the nest, incubate the eggs, and feed the chicks. House martins hunt small insects like flies and aphids while in the air. Although they are skilled flyers, they can sometimes fall prey to fast birds of prey. They may carry fleas or internal parasites. None of the house martin species are threatened, but there have been reports of declining numbers in common house martins in central and northern Europe. This decline is due to bad weather, pesticide poisoning, lack of mud for nesting, and competition with house sparrows for sites.
Delichon is a group of birds that only breeds in the Northern Hemisphere. The common house martin breeds across Europe, North Africa, and northern temperate Asia, migrating to tropical Africa for winter. The Siberian house martin breeds in northeast Russia and migrates to southern Asia for winter. The Asian house martin breeds in central and eastern Asia and typically winters in Southeast Asia, though some populations move to lower altitudes in the Himalayas and Taiwan. The Nepal house martin lives year-round in southern Asia’s mountains.
Common and Siberian house martins prefer open areas with low vegetation, such as fields and meadows, preferably near water. They can nest on human-made buildings, even in clean city centers. The other two species prefer mountainous areas and sea cliffs, nesting less often in buildings than their northern relatives. For winter, the two migrating species inhabit open and hilly areas.
Delichon martins measure 13–15 cm long, with dark blue backs, a white rump, and white or grey underparts. The common house martin is the largest at 18.3 g with the most deeply forked tail. The Nepal house martin is the smallest at 15 g with a square tail. Distinct features include the black chin and black undertail of the Nepal house martin, and the greyish wash on the underparts of the Asian house martin. Their feather molting process is slow, as they need to fly efficiently to feed. Molting typically begins when they reach their wintering grounds but overlaps with the breeding season for the Nepal house martin.
Delichon martins make simple flight calls of one to three notes. The calls of the two more common species sound like buzzing. The males produce a short, simple song that is not as melodic as those of other swallows.
House martins are easy to identify, as they do not resemble other swallows. Four species of the genus Tachycineta also have white rumps and underparts, but they have bright green or blue-green upperparts and longer tails, and are limited to Central and South America. The variable plumage of South Asian species and their complicated taxonomic history has created uncertainty about their distribution.
Originally, Delichon martins nested on cliffs, but now they mostly use human structures. Their typical nest is a mud bowl lined with grass or feathers, usually with a small opening at the top, although many Asian house martins leave their nests open.
