Habitat

Breeds mainly in coastal belts of temperate and boreal upper middle latitudes, extending into sub-Arctic and low Arctic. Breeds on small islands, rocky islets, tops of stacks, salt marshes, dredge-spoil islands, barrier beaches, and dunes on barrier islands. Breeds in many areas with Herring Gulls, but prefers more open and higher microhabitats than Herring Gull. Inland sites (Great Lakes) include islets in freshwater lakes and rivers. Early in twentieth century, Great Black-backed Gulls nested only on tops of grassy islands (Palmer 1949); meadow habitat continues to be important (Pierotti 1979, Butler and Trivelpiece 1981, Butler and Janes-Butler 1982, 1983, TPG). Nests in variety of habitats, including bare rock (TPG), shrub margins (McGill-Harelstad 1985), salt marshes (Burger 1978), and dunes (Lock 1973, Cavanagh 1992). Prefers sites on rock outcrop or pinnacle, sometimes near prominent feature (Pierotti 1979). In dense colonies, highest breeding success achieved in vegetated areas with adequate cover from intraspecific predation on semiprecocial young (TPG). Rare on bird cliffs, since confined to broad grassy ledges. Small numbers in cities nest on rooftops (Buckley and Buckley 1980).

Major requirements appear to be area free of (or inaccessible to) terrestrial predators, e.g., islands. Nest sites may be sheltered from wind; nests not oriented toward prevailing wind are often screened from nearest neighbor (TPG). Coloniality appears facultative; many Great Black-backed Gulls nest solitarily or in loose colonies.

Foraging habitat typically spatially separate from nesting habitat. See Food habits: feeding, below.

Uses open areas as roosting sites, including parking lots, fields, helipads, and airport runways. See also Breeding: nest site, below.

Abandons many offshore colonies. Largely coastal during migration, some numbers moving up large rivers and to Great Lakes. In Beauharnois, Quebec, congregates in fall and winter below dams, where dead and dying alewife (Alosa pseudoharengus) have passed through dam turbines (Steeves et al. 1989).

See Migration, above. During winter, associated with coastal communities; roosts near ports, near docks, and in estuaries (TPG). Many birds roost at landfills (Wells 1994). Adults and immatures found at sea near Georges Bank and throughout Gulf of Maine in winter (Powers 1983; see Food habits: feeding, below). In nonbreeding season, nearly all individuals associated with foraging habitats, especially during daylight; roost in areas adjacent to foraging sites.