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).

Biogeographic Regions: nearctic (Native ); pacific ocean (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: BREEDS: coastally from Alaska and islands of St. Lawrence, Pribilofs, Aleutians south to northwestern Oregon and Commander Islands. WINTERS: southeastern Alaska south along Pacific coast to southern Baja California; in Asia, Bering Islands to Japan; fairly frequent in northwestern Hawaii; casually inland in Alberta, Idaho, western Arizona, Manitoba, and Oklahoma; regular in southern Nevada (Lake Mead); recently reported from Utah (Fischer 1988).

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)

Average mass: 908 g.

Length: 66 cm

Weight: 1010 grams

• Terrestrial
• Freshwater
• Marine

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).

Aquatic Biomes: coastal

Comments: Coastal waters; shores, cliffs, rock ledges, grassy slopes, beaches, harbors of coastal cities, dumps. Nests coastally, on cliffs, rocks, grassy slopes, mostly on offshore rocks and islands; preference for sandbar islands, flat tops of rugged islands, or beaches. On estuarine islands in Washington and Oregon, nesting concentrated in areas where driftwood scattered throughout grass-forb communities (Spendelow and Patton 1988); among colonies of other seabirds.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Summer and winter ranges overlap Alaska-Oregon; migratory status in that area?

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).

Comments: Surface feeder, scavenger. Fishes, mollusks, crustaceans, garbage and carrion.

Washington and British Columbia: first-year survival was lowest September-November; survival rate was 61, 80, and 85% for first year, 2nd year, and adults, respectively (Reid 1988).

Average lifespan

Status: wild: 297 months.

L. glaucescens nests in large colonies, especially in Alaska, but also in smaller colonies to the south. Adult birds frequently return to the same colony year after year, often re-pairing with a mate from the previous year. The nest is a mound of dried plants and seaweed, sometimes fish bones and feathers, built amongst ground cover of low islands or rocky ledges of higher islands or headlands. A single brood is laid from late May to July, consisting of 2-3 buff or olive-buff eggs marked with darker brown spots. The eggs are incubated for 26-28 days. Chicks are first capable of flight around 35-54 days after hatching, attaining a fully adult plumage in the fourth year. Individual birds have been observed to live for twenty years (Campbell 1968; Murphy et al. 1984; Verbeek 1985).

Average time to hatching: 27 days.

Average eggs per season: 3.

Usually a clutch of 2-3 eggs is laid from late May into July; mean laying date is around 1st of June in western Gulf of Alaska. Incubation lasts 26-29 days. Reproductive success varies with food availability/quality (Murphy et al. 1984). Young depart nest at 40-45 days, can fly at 35-54 days, according to various reports. In Washington and British Columbia, age of first reproduction was 4-7 years in both sexes; most individuals had same mate in successive years (Reid 1988). Nests in large or small colonies; up to several thousand birds in Washington colonies (Spendelow and Patton 1988).

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).

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5B,N5N : N5B: Secure - Breeding, N5N: Secure - Nonbreeding

Rounded Global Status Rank: G5 - Secure

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

Comments: Closely related to other species within the Larus californicus complex; this complex poses one of the most complicated problems in ornithological systematics today. Hybridizes with L. occidentalis in southern British Columbia to western Oregon, withL. argentatus (on a limited basis) in south-coastal and southeastern Alaska, and with L. schistisagus in Kamchatka (AOU 1998).