The Gull-billed Tern is a medium-sized, black-capped, heavy-billed and long-legged tern, now placed by most authorities in the monotypic genus Gelochelidon (AOU 2006) but formerly placed in the larger genus Sterna (AOU 1998). It has a broad distribution, breeding in scattered localities in Europe, Asia, northwest Africa, Australia, and the Americas. Although outside the U.S. this species is less restricted to marine waters than most Sterna terns, within the U.S. it nests only in coastal colonies along the Atlantic and Gulf coasts; in southern California it is restricted to a single coastal site and one in the interior of the state. North American birds winter along the Gulf Coast, Pacific coast of Mexico, and into Central and South America.
Unlike most terns, this species has a broad diet and does not depend on fish, instead feeding commonly on insects, small crabs, and other prey snatched from the ground, air, or even bushes. It is also known to eat small chicks of shorebirds and Least Terns (Sternula antillarum), and it will pirate fish from other small terns when sharing colonies with them. Seldom abundant, this tern usually nests among Common Terns (Sterna hirundo), Black Skimmers (Rynchops niger), and in California, Caspian (Hydroprogne caspia) and Forster's terns (S. forsteri).
The Gull-billed Tern seems less tolerant of disturbance and less faithful to nest sites than Sterna terns. Sears (Sears 1978, Sears 1981) describes the breeding biology and display behavior of the eastern subspecies, G. n. aranea, in North Carolina. The breeding biology and distribution of the western subspecies, G. n. vanrossemi, were relatively unstudied until recently, but new information is summarized by Molina and Erwin (Molina and Erwin 2006) and Molina et al. (2009).