Gabbiano occidentale

Tassonomia

Nome scientifico

Larus occidentalis

Autorità

Audubon, 1839

Ordine

Caradriformi

Famiglia

Laridae

Genere

Larus

Areale e habitat

The western gull is a year-round resident in California, Oregon, Baja California, and southern Washington. It is migratory, moving to northern Washington, British Columbia, and Baja California Sur to spend the nonbreeding season.

Areale riproduttivo

NA, MA : w North Pacific coast from nw Washington to I. Guadelupe and c Baja California (nw Mexico)

Areale non riproduttivo

to s British Columbia and s Baja California (nw Mexico)

Migrazione

Complete migrants

Comportamento

The western gull rarely ventures more than approximately 100 miles inland, almost never very far from the ocean; it is almost an exclusively marine gull. It nests on offshore islands and rocks along the coast, and on islands inside estuaries. A colony also exists on Ano Nuevo Island, then Anacapa Island and Santa Barbara Island in Channel Islands National Park, and Alcatraz Island in San Francisco Bay. In the colonies, long term pairs aggressively defend territories whose borders may shift slightly from year to year, but are maintained for the life of the male.[citation needed]<p>Western gulls feed in pelagic environments and in intertidal environments. At sea, they take fish and invertebrates like krill, squid and jellyfish. They are unable to dive and feed exclusively on the surface of the water. On land they feed on seal and sea lion carcasses and roadkill, as well as cockles, starfish, limpets and snails in the intertidal zone. They also feed on human food refuse, in human-altered habitats including landfills, and take food given to them, or stolen from people at marinas, beaches and parks. Western gulls are known to be predatory, killing and eating the young of other birds, especially ducklings, and even the adults of some smaller bird species. Western gulls, including one who lived at Oakland's Lake Merritt are known for killing and eating pigeons (rock doves). They will also snatch fish from a cormorant's or pelican's mouth before it is swallowed. The bird has also been observed directly pilfering milk from the elephant seal's teat.

Conservazione

Tendenza della popolazione

rising