The major breeding grounds for Heermann’s Gulls (Larus heermanni) are islands in the Gulf of California, especially Isla Raza, where an estimated 80,000 pairs nest (Lindsay, Proc. Calif. Acad. Sci., ser. 4, 30:309–355, 1966). On the western side of the Baja California peninsula only one colony has been reported, at Isla San Roque (27°09′ N) (Grinnell, Univ. Calif. Publ. Zool. 32:1–300, 1928). In August 1922 A. W. Anthony (Proc. Calif. Acad. Sci., ser. 4, 14:277–330, 1925) visited San Roque and reported that the colony seemed to have been destroyed by fishermen.