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Distribution and habitat

The family has a worldwide cosmopolitan distribution, breeding on every continent except Antarctica. One species, the Pacific swallow, occurs as a breeding bird on a number of oceanic islands in the Pacific Ocean, the Mascarene martin breeds on Reunion and Mauritius in the Indian Ocean, and a number of migratory species are common vagrants to other isolated islands and even to some sub-Antarctic islands and Antarctica. Many species have enormous worldwide ranges, particularly the barn swallow, which breeds over most of the Northern Hemisphere and winters over most of the Southern Hemisphere.

The family uses a wide range of habitats. They are dependent on flying insects, and as these are common over waterways and lakes, they frequently feed over these, but they can be found in any open habitat, including grasslands, open woodland, savanna, marshes, mangroves, and scrubland, from sea level to high alpine areas. Many species inhabit human-altered landscapes, including agricultural land and even urban areas. Land-use changes have also caused some species to expand their range, most impressively the welcome swallow, which began to colonise New Zealand in the 1920s, started breeding in the 1950s, and is now a common landbird there.

Species breeding in temperate regions migrate during the winter when their insect prey populations collapse. Species breeding in more tropical areas are often more sedentary, although several tropical species are partial migrants or make shorter migrations. In antiquity, swallows were thought to have hibernated in a state of torpor, or even that they withdrew for the winter under water. Aristotle ascribed hibernation not only to swallows, but also to storks and kites. Hibernation of swallows was considered a possibility even by as acute an observer as Rev. Gilbert White, in his The Natural History and Antiquities of Selborne (1789, based on decades of observations). This idea may have been supported by the habit of some species to roost in some numbers in dovecotes, nests and other forms of shelter during harsh weather, and some species even entering torpor. There were several reports of suspected torpor in swallows from 1947, such as a 1970 report that white-backed swallows in Australia may conserve energy this way, but the first confirmed study that they or any passerine entered torpor was a 1988 study on house martins.