Western Gull
| Western Gull | ||||||||||||||
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 L. occidentalis | ||||||||||||||
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| Binomial name | ||||||||||||||
| Larus occidentalis (Audubon, 1839) |
The Western Gull, Larus occidentalis, is a large white-headed gull that lives on the western 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 Washington and British Columbia to Baja California, and because of its well placed colonies on the coast of California it is a well studied species. Despite being a well known species on the USA West Coast it is of slight conservation concern given its restricted range (for a gull).
Description
The Western Gull is a large gull (around 60 cm long) with a white head and body, and gray wings. It has yellow bill with a red subterminal spot (the small spot at the end of a gull's bill that chicks peck in order to be fed). 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).
Behaviour
The Western Gull is an exclusively marine gull that is seldom encountered inland. It nests on offshore islands and rocks along the coast, and also on islands inside estuaries, and a colony exists on Alcatraz Island in San Francisco Bay. On 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. The Western Gull typically lives 15 years, but is known to live at least 25 years.
A nest of vegetation is constructed inside the territory, and three eggs are laid. These eggs are incubated for a month. The chicks, when born, remain inside the territory until they have fledged, chicks straying inside the territory of another gull are liable to be killed by that territory's pair. On occasion abandoned chicks will be adopted by other gulls.
Western Gulls feeds in pelagic and intertidal environments. At sea they take fish and invertebrates like krill, squid and jellyfish. They cannot dive, and feed exclusively on the surface. On land they will feed on seal and sea lion carcasses, as well as cockles, limpets and snails in the intertidal zone. They will also use human-altered habitats, feeding at landfills and taking food from people at marinas and beaches.
Western Gulls and Man
The Western Gull is currently not considered threatened. Its numbers were greatly reduced in the 19th century by the taking of seabird eggs for the growing city of San Francisco, it also suffered from disturbance at its colonies were they were turned into lighthouse stations, or, in Alcatraz's case, a prison. The Western Gulls are very aggressive when defending their territories and consequently were persecuted as a menace. The automating of these 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.
The Western Gull was one of the protagonists in Alfred Hitchcock's famous movie, The Birds, which was filmed in Bodega Bay, California, near the biggest Western Gull colony, the Farallon Islands.
fr:Goéland d' Audubon