The Gull-billed Tern breeds in Southern Europe, a very small isolated population in northern Germany and Denmark, temperate and eastern Asia, both coasts of North America, eastern South America and Australia. There are several geographical races of this bird, differing mainly in size and minor plumage details.
The Gull-billed Tern has the appearance of a 'white' (Sterna) tern, but the feeding habits of a Chlidonias marsh tern, like the Black Tern and White-winged Tern.It used to be grouped in the genus Sterna but is now placed on its own in the genus Gelochelidon.
The Gull-billed Tern is a fairly large tern, similar in size and appearance to a Sandwich Terns, but the short thick gull-like bill, broad wings, long legs and robust body set it apart.
Juvenile Sandwich Terns have a cute short bill, and are frequently mistaken for Gull-billed Tern where the latter species is uncommon, such as North Sea coasts.