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The Western Gull (Larus occidentalis) is a large white-headed gull that lives on the west coast of North America. It was previously considered conspecific with the yellow-footed gull (Larus livens) of the Gulf of California. The western gull ranges from British Columbia, Canada to Baja California, Mexico.

It is a large gull that can measure 22 to 27 inches in total length, and wing span of 51 to 57 inches. The western gull has a white head and body, and gray wings. It has a yellow bill with a red subterminal spot. It closely resembles the slaty-backed gull (Larus schistisagus). In the north of its range it forms a hybrid zone with its close relative the glaucous-winged gull (Larus glaucescens).

Western gulls take approximately four years to reach their full plumage, their layer of feathers and the patterns and colors on the feathers. The western gull typically lives about 15 years, but can live up to 25 years. The largest western gull colony is on the Farallon Islands, located about 26 mi west of San Francisco, California; an estimated 30,000 gulls live in the San Francisco Bay area.

The western gull rarely ventures more than approximately 100 miles inland, 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 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.

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 from people at marinas, beaches and parks.

Western gulls are known to be predatory, killing and eating the young of other birds and even the smaller adults of some 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.

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 western gull is currently not considered threatened. However, they have, for a gull, a restricted range. Numbers were greatly reduced in the 19th century by the taking of seabird eggs 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.

Western gulls are very aggressive when defending their territories and consequently were persecuted by some as a menace. The automation of lighthouses and the closing of Alcatraz Prison allowed the species to reclaim parts of its range. They are currently vulnerable to climatic events like El Niño events and oil spills.

Western gulls have become a serious nuisance to the San Francisco Giants baseball team. Thousands of gulls fly over AT&T Park in San Francisco during late innings of games. They swarm the field, defecate on fans, and after games eat leftovers of stadium food in the seats; how the birds know when games are about to end is unknown. The gulls left while a red-tailed hawk visited the park in late 2011, but returned after the hawk disappeared. Federal law prohibits shooting the birds, and hiring a falconer would cost the Giants $8000 a game.

These photos were taken during a pelagic trip as part of the San Diego Bird Festival.

Western Gull