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(in Russian, bolotnye krachki), a genus of birds of the gull family. The name includes three varieties: the black tern (C. nigra), white-winged tern (C. leucoptera),and whiskered tern (C. hybrida). Body length is 25–28 cm. Plumage is bluish black with white; the black tern has a white rump, the white-winged has white upper covert feathers, rudder feathers, and undertail, and the whiskered has white cheeks and throat. Widely distributed (excluding the north) in Europe, Asia, and North America, as well as in Africa and Australia, Chlidonias is a migratory bird. It nests in colonies in swampy meadows, swamps, and the shores of reservoirs overgrown with thick grassy vegetation. There are two to three eggs per laying; both parents sit on the eggs (18 days).