The Western Gull breeds on islands along the Pacific coast of North America from southern Washington to southern Baja California but, before the observations we report here, had never been reported breeding in the Gulf of California (American Ornithologists’ Union 1998; Everett and Anderson 1994; Howell and Webb 1995; Pierotti and Annett 1995; Wilbur 1987). Non-breeding individuals, mostly immature, range into the Gulf of California as far north as Puerto Peñasco and as far south as Bahía Guásimas (Russell and Monson 1998). They are frequently found among Yellow-footed Gulls (Larus livens).