During the 2003 and 2005 breeding seasons we conducted ground surveys of historical, potential, and current nesting sites of the VanRossem’s Gull-billed Tern (Gelochelidon nilotica vanrossemi) along the Pacific coast of Mexico. We documented 13 active colonies, including ten previously unrecorded nesting sites. One previously reported colony was inactive. Colony sizes ranged between one and 161 breeding pairs. In 2005, the estimated breeding population size was 526 pairs. Eighty-two percent of the total breeding population was concentrated in three relatively large colonies, Cerro Prieto and Isla Montague, Baja California and Laguna Las Garzas, Nayarit. Gull-billed Terns nested mostly on islets in very shallow waters. Colony associates included other terns, Black Skimmers (Rhynchops niger), gulls, and egrets. The nesting population of this subspecies in Mexico is very small and consists of a few widely separated colonies. This subspecies should be included in Mexico’s official list of species at risk, and a management plan should be developed and implemented to assure its conservation and that of the wetland habitat on which it and other bird species depend.
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Vol. 30 • No. 2