Introduction

Adult Gull-billed Tern, breeding plumage; New Jersey, July

Figure 1. Distribution of the Gull-billed Tern in North and Middle America.

Adult Gull-billed Terns, breeding plumage; Texas; April.

Juvenile Gull-billed Tern, Salton Sea, CA; early August.

Editor’s Note: Study of the mitochondrial DNA of terns, along with their plumage characteristics, have suggested that the heretofore broadly defined genus Sterna is paraphyletic. Reclassification of this genus now places Gull-billed Tern in the genus Gelochelidon. See the 47th Supplement to the AOU Check-list of North American Birds for details. Future revisions of this account will account for this change.

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 (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, were relatively unstudied until recently, but new information is summarized by Molina and Erwin (2006) and Molina et al. (2009).