SIMoN
  Sanctuary Integrated Monitoring Network
SIMoN Tools

Species Database

Larus occidentalis - Western Gull

Western Gull image

Geographic range:

British Columbia, Canada to Baja California, Mexico

Key features:

Adult Larus occidentalis is dark slaty gray above with the head, tail and underparts white. The eyes are yellowish and its legs are pink. The bill is large, yellow, and has a red spot near the tip.

Similar species:

Larus californicus -- California Gull
Larus glaucescens -- Glaucous-winged Gull

Habitat(s):

bay (rocky shore), bay (sandy shore), estuary, exposed rocky shore, exposed sandy beaches, kelp forest, protected rocky shore, protected sandy beaches
 

Primary common name:

Western Gull

General grouping:

Seabirds and shorebirds

ITIS code:

176817
 

Geographic Range

Range Description:

Larus occidentalis can be found from southern British Columbia to Baja California. It is rarely reported east of the Rocky Mountains.

Habitats

bay (rocky shore), bay (sandy shore), estuary, exposed rocky shore, exposed sandy beaches, kelp forest, protected rocky shore, protected sandy beaches

Habitat notes:

Larus occidentalis occupies many types of habitats, including estuaries, beaches, fields, garbage dumps, and city waterfronts. Nest sites are often located on rocky, sandy, or gravel islands, or inaccessible mainland cliffs. Larus occidentalis is common at sea out to 117 km from shore.

Abundance

Relative abundance:

Larus occidentalis is abundant throughout the year.

Species Description

General description:

Larus occidentalis is a large gull, around 60 cm long with a white head and body, and gray wings. 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). Larus occidentalis is a four year gull, meaning that it takes four years to achieve adult plumage and breeding age.

Distinctive features:

Adult Larus occidentalis is dark slaty gray above with the head, tail and underparts white. The eyes are yellowish and its legs are pink. The bill is large, yellow, and has a red spot near the tip (this is the small spot near the end of the bill that chicks peck in order to stimulate feeding). At first winter, 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.

Size:

Larus occidentalis can grow to a length of 64 cm and have up to a 147 cm wingspan.

Natural History

General natural history:

Larus occidentalis is an exclusively marine gull and is seldom encountered inland. Primarily a coastal breeder, with the bulk of the population nesting in Oregon and California, it nests on offshore islands and rocks along the coast, and on islands inside estuaries, and a colony also exists on Alcatraz Island in San Francisco Bay. In the colonies, long term pairs aggressively defend their territories. While the borders of these territories may shift slightly from year to year, they are maintained for the life of the male. Larus occidentalis typically lives 15 years, but can live to at least 25 years.

Prey:

Larus occidentalis is an omnivore that eats a variety of things including fish and other aquatic creatures, eggs, carrion, garbage, and other birds.

Feeding behavior

Carnivore, Omnivore, Scavenger

Feeding behavior notes:

Larus occidentalis feeds in pelagic as well as intertidal environments. At sea they may take fish and invertebrates like krill, squid and jellyfish. Since they cannot dive, they feed exclusively on the surface. On land they will feed on seal and sea lion carcasses, and in the intertidal zone they will feed on cockles, limpets and snails. Larus occidentalis will also use human-altered habitats, feeding at landfills and taking food from people at marinas and beaches. At times they can be predatory, preying on the young of other birds and even adults of some species.

December - February

Migration:

In the winter Larus occidentalis expands its range somewhat, migrating further north, south or even wandering upstream along the Columbia River system.

June - August

Reproduction:

Larus occidentalis breeds in colonies, often with other gull species, on rocky offshore islands along the Pacific coast. Gulls will establish their own territory inside the breeding area, and will there construct a nest on the ground that is composed of vegetation, feathers, rope, plastic and other items. Usually three eggs are laid, and both parents participate for the next month in incubating the eggs. Once the chicks are hatched, they are incubated for a month with both members of the nesting pair incubating the egg. The chicks, once hatched, remain inside the territory until they have fledged. If they stray into the territory of another gull, they are liable to be killed by that territory\'s pair. Chick mortality is high, with on average one chick surviving to fledging. On occasion, abandoned chicks will be adopted by other gulls.
Click on an image below to view a larger version in the SIMoN Photo Library. You will also be able to view important information on each photo such as photographer, date, caption and more.
Alden, P., F. Heath, R. Keen, A. Leventer, and W. Zomlefer. 2002. National Audubon Society Field Guide to California. A.A. Knopf, New York, NY.
Bird Information Website. 2006 (Updated 02/02/06). World Wide Web electronic publication. http://www.birdinfo.com/WesternGull.html, Accessed [04/22/06].
Dunn, J.L. 1999. Birds of North America. National Geographic, Washington, D.C. 464 p.
Stallcup, R. 1990. Ocean Birds of the Nearshore Pacific. Point Reyes Bird Observatory, Stinson Beach, CA. 214 p.
WWW
Cornell Lab of Ornithology
All About Birds
http://www.allaboutbirds.org/guide/search
Accessed 05/17/2009 for Albatross
Accessed 01/15/2009 for Clark's Grebe
Accessed 01/20/2009 for Great Egret
Accessed 02/03/2009 for American White Pelican
Accessed 01/30/2009 for Pelagic Cormorant
Accessed 02/12/2009 for Black-necked Stilt
Accessed 02/28/2009 for Marbled Godwit
Accessed 03/15/2009 for Whimbrel
Accessed 04/11/2009 for Long-billed Curlew
Accessed 04/13/2009 for Heermannís Gull
Accessed 09/10/2009 for Eared Grebe
Accessed 11/11/2009 for American Avocet
Accessed 01/26/2010 for Pigeon Guillemot
Accessed 12/15/2009 for Black-crowned Night Heron
Accessed 07/07/2009 for Pied-billed Grebe
Accessed 04/04/2010 for Osprey
Accessed 08/30/2010 for Ruddy Turnstone
Accessed 10/10/2010 for Pacific Loon
Accessed 10/15/2010 for Sooty Shearwater
Accessed 10/30/2010 for Surf Scoter
Accessed 12/04/2010 for Bufflehead
Accessed 02/01/2011 for American Coot
Accessed 02/20/2011 for Western Sandpiper
Accessed 03/04/2011 for Least Sandpiper.
Accessed for California Condor

WWW
Seattle Audubon Society.
http://www.seattleaudubon.org/birdweb/
Accessed 01/30/2009 for Pelagic Cormorant
Accessed 02/28/2009 for Marbled Godwit
Accessed 04/13/2009 for Heermannís Gull
Accessed 03/15/2009 for Whimbrel
Accessed 06/20/2010 for Black Turnstone
Accessed 12/15/2009 for Black-crowned Night Heron
Accessed 02/01/2011 for American Coot