The common house martin (Delichon urbicum), sometimes called the northern house martin or, particularly in Europe, just house martin, is a migratory passerine bird of the swallow family which breeds in Europe, north Africa and across the Palearctic; and winters in sub-Saharan Africa and tropical Asia. It feeds on insects which are caught in flight, and it migrates to climates where flying insects are plentiful. It has a blue head and upperparts, white rump and pure white underparts, and is found in both open country and near human habitation.
Both the scientific and colloquial name of the bird are related to its use of human-made structures. It builds a closed cup nest from mud pellets under eaves or similar locations on buildings usually in colonies.
The adult common house martin of the western nominate race is 13 cm (5.1 in) long, with a wingspan of 26–29 cm (10–11 in) and a weight averaging 18.3 g (0.65 oz). It is steel-blue above with a white rump, and white underparts, including the underwings; even its short legs have white downy feathering. It has brown eyes and a small black bill, and its toes and exposed parts of the legs are pink
The common house martin is a noisy species, especially at its breeding colonies. The male’s song, given throughout the year, is a soft twitter of melodious chirps. The contact call, also given on the wintering grounds, is a hard chirrrp, and the alarm is a shrill tseep.
The preferred habitat is open country with low vegetation, such as pasture, meadows and farmland, and preferably near water, although it is also found in mountains up to at least 2,200 m (7,200 ft) altitude. It is much more urban than the barn swallow, and will nest even in city centres if the air is clean enough.
The common house martin returns to the breeding grounds a few days after the first barn swallows; like that species, particularly when the weather is poor, it seldom goes straight to the nesting sites, but hunts for food over large fresh water bodies.