Housemartins are small migratory birds belonging to the family Hirundinidae. They are known for their distinctive white underparts and blue-black upperparts. These birds typically build their nests under the eaves of buildings or in cliff faces, using mud and grass to create a cup-shaped structure. Housemartins primarily feed on insects, which they catch in flight. They are often seen flying in groups, performing acrobatic maneuvers as they hunt for food. These birds are common in Europe and parts of Asia and Africa, migrating south for the winter to warmer climates.