The Western gull is a large seabird that lives on the west coast of North America. It has a white head and body, gray wings and yellow bill. In Washington state, the Western gull hybridizes frequently with the Glaucous-winged gull, and may closely resemble a Thayer's gull. The hybrids have a flatter and larger head and a thicker bill with a pronounced angle on the lower part of the bill, which distinguishes it from the smaller Thayer's gull.
The range of Western gulls extends from British Columbia, Canada to Baja California, Mexico. These birds are found at sea, on offshore islands and rocks along the coast, on islands inside estuaries, and on beaches.
Western gulls are almost exclusively marine birds and rarely venture far from the ocean. They are social but territorial; in the colonies pairs aggressively defend territories whose borders may shift slightly from year to year, but are maintained for the life of the male. Western gulls are active during the day. They are unable to dive and feed exclusively on the surface of the water. Western gulls are noisy birds and have a loud “keow” call or a rapid “quock-kuk-kuk-kuk”.
Western gulls are carnivores and scavengers. At sea, they eat fish and invertebrates like krill, squid, and jellyfish. On land, they feed on the 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, and take food given to them, or stolen from people at marinas, beaches, and parks. Western gulls may also eat the young of other birds, especially ducklings, and even the adults of some smaller bird species.
Western gulls are monogamous and mate for life. They nest in colonies on offshore islands or rocks along the coast. A nest of vegetation is constructed on the ground inside the parent's territory. The female lays 3 eggs and both parents incubate them for a month. The chicks, once hatched, are able to leave the nest a few days after hatching but remain inside the territory until they have fledged. They begin to fly at 6-7 weeks of age and become independent when they are 10 weeks old. Young Western gulls reach reproductive maturity and are ready to breed for the first time at 4 years of age.
Western gulls are currently not considered threatened. However, they have a restricted range. Their numbers were greatly reduced in the 19th century by the egg collection for the growing city of San Francisco. Western gull colonies also suffered from disturbance where they were turned into lighthouse stations, or, in the case of Alcatraz, a prison. These birds are very aggressive when defending their territories and consequently were persecuted by some as a menace. They are currently vulnerable to climatic events like oil spills and El Niño (temperature fluctuation of the surface water layer in the equatorial part of the Pacific Ocean, which has a noticeable effect on the climate).
According to the IUCN Red List, the total population size of Western gulls is 115,500-118,500 individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are increasing.