Larus glaucoides

Formerly (e.g., AOU 1983, 1998) treated as two species L. glaucoides and L. thayeri Brooks, 1915 [Thayer's Gull], but merged based on evidence of non-assortative mating between thayeri and kumlieni on Baffin and Southampton islands (Weber 1981, Gaston and Decker 1985, Snell 1989), and doubts concerning the validity of the study (Smith 1966) cited by AOU (1973) for treating thayeri as separate from glaucoides (Snell 1989, 1991). The status of kumlieni, the variable form intermediate between thayeri and glaucoides, is poorly known due to the relative inaccessibility of its breeding areas; we retain it here as a separate group within L. glaucoides pending further research.

Breeding: southern Baffin Island, extreme northwestern Quebec, Greenland, Iceland, Jan Mayen, and Banks, southern Melville, Cornwallis, Axel Heiberg, and central Ellesmere islands south to southern Victoria Island, northern Kivalliq, northern Southampton and northern Baffin islands, and on northwestern Greenland. L. g. thayeri sometimes summer in the wintering range. Non-breeding: from Newfoundland south on Atlantic coast to North Carolina and Bermuda and inland rarely to Great Lakes (also Old World), and from coastal western North America primarily from southern British Columbia south to southern California and central Baja California. Nonbreeders widespread in northern North America in summer. Casual [thayeri group] in western Europe (Iceland, Norway, Denmark, Ireland, England, the Netherlands, and Spain), Japan, and Korea; [kumlieni group] in interior and northwestern North America; and [glaucoides group] in northeastern North America. Accidental [thayeri group] in Kamchatka; and [glaucoides group] in Ontario, Alaska, California, Florida, and Novaya Zemlya, although extralimital records of individuals are often difficult to identify to group with certainty.