The Mew Gull is a characteristic bird of beaches and river estuaries along the Pacific coast in winter and is the smallest of the “white-headed” gulls in North America, where it was formerly known as the Short-billed Gull. Its breeding range on this continent is confined to northwestern portions, but it has a nearly circumpolar distribution, occurring across a substantial stretch of Eurasia, where it is also called the Common Gull. Because of its extensive range with rather marked differences among European, northeast Asian (known as Kamchatka Gull), and North American populations, taxonomic treatment of this species has varied, with 2 to 3 species sometimes recognized. Its world population is probably in excess of 1 million pairs.
This gull is remarkable for the plasticity of its habitat selection and for its reproductive and feeding behaviors. It is facultatively colonial, and colony size can range from a few to several hundred pairs. It breeds in both marine and freshwater habitats and is both a ground and tree nester, being the only “white-headed” gull that regularly uses trees for nesting. It occupies a wide variety of habitats, several of which are used in both summer and winter, including lakes, rivers, and rocky shores. In addition, during the breeding season, it uses tundra, marshes, streams, and islands. In winter, North American breeders chiefly forage over inshore and near-offshore marine waters, lagoons, and river estuaries; they are mainly coastal, being rare far offshore. Onshore, Mew Gulls may frequent flooded fields and short-grass pastures and are common, and perhaps best known, around sewage-treatment ponds and outfalls in coastal communities. This bird eats fish in coastal waters and insects and other invertebrates both along the coast and inland; occasionally, it will feed on grains and berries, depending on the availability of the main items in its diet. It employs a variety of foraging techniques, including kleptoparasitism. Nest sites depend on what is available locally, but are typically selected because they offer protection against predators and inclement weather. Because the Mew Gull has been studied in Europe as well as North America, its life history is well known.
In North America, significant research has been done on Mew Gull breeding biology in British Columbia ( Vermeer and Devito 1986 ) and Alaska (south-central region by Burger and Gochfeld [ Burger and Gochfeld 1987 ] and the Anchorage area by Adamson [ Adamson 1988 ]). Habitat selection has been studied in British Columbia ( Vermeer and Devito 1987 ) and south-central Alaska ( Burger and Gochfeld 1988b ) and foraging behavior on Puget Sound ( Tangren 1982 ), in Anchorage ( Adamson 1988 ), and in British Columbia ( Vermeer et al. 1987c ). In Europe, extensive work has been done on the relationship between sexual and agonistic behavior ( Weidmann 1955 ), breeding behavior in Ireland ( Whilde 1984 ), growth energetics ( Kahru and Kespaik 1983 ), habitat selection in Poland ( Wesolowski et al. 1985 ), nest-site selection in Finland ( Von Haartman 1980 ), population ecology in Estonia ( Rattiste and Lilleleht 1987 ), and nest-defense behavior in Finland ( Kilpi 1988 ).