Systematics

Lighter plumage populations in n. Alaska and Mackenzie Delta, Northwest Territories (NWT), once described as Nelson’s Gull (Larus nelsoni), later considered hybrids with Glaucous Gulls or less melanistic Herring Gulls (Snell 1991). Thayer’s Gull may be subspecies of Herring or Iceland Gull (Cramp and Simmons 1983, Harrison 1983).

L. argentatus smithsonianus only recognized subspecies that breeds in North America. Nine subspecies recognized in Europe and Asia divided into northern or nominate “ argentatus ” group and southern or nominate “cachinnans” group (Cramp and Simmons 1983). L. a. smithsonianus member of nominate “argentatus” group (Grant 1986). Hybrids formed with other large white-headed gulls in regions of overlap (Pierotti 1987b); has interbred with Great Black-backed Gull around Ottawa, Ontario (Pierotti 1987b), with Glaucous-winged Gull on Kenai Peninsula and in se. Alaska (Patten 1980), and with Glaucous Gull in n. Alaska and Northwest Territories (Spear 1987). Glaucous-winged Gull x Herring Gull hybrids also documented in Utah (Fischer 1988). Close genetic similarity among Canadian, Icelandic, and European populations of Herring, Glaucous, Great Black-backed, and Iceland gulls indicated by extremely small Nei’s D values (0.000–0.009) and Roger’s D distances (0.004–0.032) (Snell 1991).

American Birds records suggest (1) L. a. vegae (Asian race) regular visitor to w. Alaska; (2) possible records for L. a. argentatus in Newfoundland; (3) birds from s. European L. (a.) cachinnans complex recorded at least twice in North America. Yellow legs of L. cachinnans probably indicate reproductive isolation from L. argentatus (Pierotti 1987, Panov 1989). Evidence from mitochondrial cytochrome b gene indicates that L. argentatus and L. cachinnans are distinct species with cachinnans more closely related to L. fuscus, which also has yellow legs (Wink et al. 1994).