Black Tern

The black tern is a small marsh tern, named for the dark breeding plumage that can look bluish in some light. Adults have short dark legs, a slender black bill, dark grey back, pale forewing and a short, nearly square tail. Breeding birds show a black head, neck and belly, whereas the face is white outside that plumage. Juveniles carry a broad white collar and a large dark triangular patch in front of the eye. (Wikipedia, black tern account)

Unlike many marine terns, the black tern is generally associated with inland water during the breeding season. It nests across Europe, western Asia and North America, then migrates to coastal areas of Africa or South America for winter. Two subspecies are recognized. The nominate form breeds from inland continental Europe east through central Asia and southern Russia to northwestern Mongolia, providing a specifically documented regional connection for Mongolian records rather than a range inferred from neighbouring countries. (Wikipedia, black tern account)