Introduction

The Gull-billed Tern is a medium-sized, black-capped, heavy-billed tern with 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 other Sterna terns, within the U.S. it nests only in coastal colonies along the Atlantic and Gulf coasts, and in southern California is restricted to two saline sites. 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 other terns, and it will pirate fish from them in mixed nesting colonies with them. Seldom abundant, this tern usually nests among Common Terns (Sterna hirundo), Black Skimmers (Rynchops niger), and in California, Caspian Terns (S. caspia) and Forster’s Terns (S. forsteri). The Gull-billed Tern seems less tolerant of disturbance and less faithful to nest sites than other Sterna terns. Sears (1978, 1981) describes the breeding biology and display behavior of the eastern subspecies, S. n. aranea, in North Carolina. The breeding biology and distribution of the western subspecies, S. n. vanrossemi, have only recently received attention and remain poorly known.