Larus glaucescens
glaucous-winged gull

Larus glaucescens nests on rocky cliffs among the seabird colonies of the coastal northern Pacific, from Alaska and the Aleutians south to northern Washington state. Winters from southern Alaska to south along the Pacific coast as far as Baja California, occasionally in the eastern Hawaiian islands (Godfrey 1986).

L. glaucescens lives primarily in the vicinity of salt or brackish water along coasts: bays, estuaries, islands, beaches, mud flats, and nearby offshore. It can also be found around wharves, dumps, fish canneries, and fishing boats. It sometimes follows rivers, but is not normally found very far inland (Godfrey 1986).

Adults of L. glaucescens have a body length of 24-27 inches, and a wingspan of around 54 inches, males larger than females. Adults are white with a pale grey back (hence specific name glaucescens: Latin for greying, from Greek glaukos, blue-grey). Wings are also pale grey, with small white patches. Large, heavy yellow bill with red spot. Skin around eyes purplish pink, iris silver to yellow powdered with brown, giving a dark appearance. Juvenile birds have a dark bill, and mottled grey plumage (Hoffman et al. 1978; Godfrey 1986)

L. glaucescens is territorial upon the breeding grounds, resulting in frequent squabbles between adult birds, most often the males. It is gregarious throughout the year, even with different gull species. Calls are described as similar to those of the Herring Gull (L. argentatus), involving a variety of prolonged wails, chuckles, and hisses, as well as the food-begging calls of young birds. The red spot on the adult bill is believed to stimulate a pecking response from the young chicks, which in turn causes the parent to regurgitate food for the chick (Verbeek 1985; Godfrey 1986).

L. glaucescens is omnivorous, feeding on carrion, fish, invertebrates, seaweed, and food stolen from other marine birds (pelicans, cormorants, sea ducks). During periods of lowest tidal heights mussels and barnacles comprise much of their diet, but at other times sea urchins, chitons, and limpets are preferentially gathered. Barnacles, sea urchins, molluscs, and other resistant food items are gathered from the shore and dropped onto rocks from the air to crack them open. In the vicinity of humans L. glaucescens will scavenge garbage from docks, dumps, and shores, and follow fishing vessels. It may also forage over the open ocean, but rarely to more than a few miles offshore (Murphy et al. 1984; Irons et al. 1986).

Being a scavenger on human wastes, L. glaucescens can be considered a pest in areas of high population, but never to any harmful level.

L. glaucescens winters in coastal Pacific waters to the southern Baja, and though it is not threatened in any of these areas it is protected under the U.S. Migratory Bird Treaty Act. The population of L. glaucescens has increased around three and a half times in the last 50 years, mostly due to accessibility of human wastes (Verbeek 1985).

Interbreeding between L. glaucescens and the Herring Gull is common and widespread in Alaska, and a single mating pair of these species was known from Okanagan Lake, British Columbia. L. glaucescens also hybridises with the Western Gull (L. occidentalis) along the coast of Oregon and Washington states (Williamson and Peyton 1963; Merilee 1974; Hoffman et al. 1978).