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    Channel Islands

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Western Gull

Robert Schwemmer
 

Scientific Name
Larus occidentalis

Introduction
Western gulls are the most abundant breeding seabird in the Channel Islands National Park, with a population estimated at more than 15,000. The western gull, a big bulky bird, is a bold, skillful hunter and scavenger. For the most part, western gulls are coastal dwellers that concentrate mainly in the Southern California area. Due to their opportunistic nature and adaptability, they can also thrive in an urban environment. Unfortunately, because of close proximity to human environs, they are also subject to abnormal environmental pressures.

Quick and Cool Facts

  • Found along the along Pacific Coast of North America with breeding sites from central Baja California north to Washington.
  • Relatively limited in distribution compared to most North American gulls.
  • Large colonies are found on Santa Barbara and Anacapa Islands.
  • Western Gulls nest on offshore islands, rocks along the coast, and on islands inside estuaries.
  • They nest on the ground and fill the nest with vegetation, feathers, rope, plastic, or other items they find.
  • In colonies with many more females than males present, two females may establish a pair bond. Each lays eggs, and then takes care of the double-sized brood.
  • The female-biased sex ratio of some western gull colonies may have been the result of pollution by pesticides that acted like estrogen and made some male embryos develop as females.
  • It takes four years for a western gull to achieve its gray and white appearance.
  • They can live up to 25 years old.
  • Western gulls feed only on the ocean's surface and do not dive like many other seabird species.
  • Like most gulls, the western gull is an opportunistic feeder, capturing its own live prey, scavenging refuse, or stealing food from seals and other gulls.

Appearance
The adult western gull has a deep gray back and wings, with black wing-tips that blend into the rest of the wing, unlike many species where the black is clearly defined. The underwing is white with a narrow band of gray. The head is mostly white, with a limited amount of brown streaking, especially in non-breeding plumage. The large bill is yellow with a red spot, and the eye is dark yellow. The western gull is a four-4 year gull, meaning that it takes four years to achieve adult plumage. Juveniles are mottled brown, with a dark bill and dark eyes, and pinkish-gray legs. This plumage varies and takes on more of the adult plumage characteristics in each successive year.

Range
The western gull is confined to the immediate Pacific coast and its adjacent waters. The bird usually breeds on near-shore islands and human-made structures, but searches for food at sea, along estuaries, and on the shoreline. Wintering gulls may move farther out to sea, but also forage and rest on buildings, parking lots, seaside parks, landfills, and jetties.

Habitat
The islets of Anacapa, which is part of the Channel Islands National Park, hosts the largest protected breeding colony of western gulls in the world with over 10,000 gulls gathering during nesting season from May through July. There is also a sizeable colony of western gulls (approximately 7,000 pairs) on Santa Barbara Island.

Feeding
Western gulls feed over the open ocean or along rocky shores. When the western gull spots its prey, it captures it by pecking, grabbing, and shallow diving. The bird's omnivorous diet includes squid, clams, mussels, sea urchins, eggs, chicks, adult birds, zooplankton, and small fish like anchovy, whiting, eel, and rockfish. Other oceanic species use the western gull to find prey. In turn, this gull may follow seals to locate food. This resourceful bird scavenges the carcasses of large mammals and when their normal sources of food are diminished, gulls are quick to take advantage of an easy food source such as trash and leftover scraps. By exploiting unnatural food resources their population may be growing larger than it would naturally thus upsetting the ecosystem balance.

Reproduction
Western gulls choose a nest site out of the wind, and out of sight from other gulls. In colonies with many more females than males present, two females may establish a pair bond. Each lays eggs, and then takes care of the double-sized brood. In late April or May, the female lays two to three light olive to green eggs with dark markings. Both parents incubate; after 4 -5 weeks the gray, downy chicks with black spots hatch. Within a day, the chicks can walk and soon leave the nest. They freely scramble after regurgitated food. If the third chick is not fed enough, it may leave the territory. Neighboring gulls sometimes kill wayward chicks, but adoption is frequent. Chicks play by chasing or tugging on objects. Juveniles fledge in about seven weeks and are usually fed for three months, but sometimes follow adults and beg for up to six months.

Migration
Many western gulls do not migrate; the rest cover very short distances to remain on the Pacific coast of North America. Some move south of the breeding range into Baja California. Fall movements peak in October and most adult birds return to their breeding grounds in March.

Conservation Status
Populations of western gulls have restricted range and therefore, are vulnerable to oil pollution, ocean acidification, and climate change. In addition, they have also suffered from human disturbances and in the past, introduced black rats on Anacapa Island. Visit Seabirds for more information about restoration activities on Anacapa to remove black rats.

Links for Additional Information

Did You Know?

1994 pygmy mammoth excavation, Santa Rosa Island

The world's most complete pygmy mammoth specimen was discovered on Santa Rosa Island in 1994. These miniature mammoths, only four to six feet tall, once roamed island grasslands and forests during the Pleistocene.