- 22–26 in
- 47.2–56.7 in
- 28.2–44.1 oz
- Goéland d'Audubon (French)
- Gaviota occidental (Spanish)
- 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. It is known to steal milk from lactating female seals while they lie on their backs sleeping on the beach.
- The Western Gull hybridizes extensively with the Glaucous-winged Gull, with the hybrids being the most common form in Washington. The hybrids can be similar to the parent adult forms, but usually have intermediate back and wingtip coloring. With the medium-gray back, dark upper surface to wingtips, frosty white undersurface to wingtips and a darkish eye, a hybrid may closely resemble a robust Thayer's Gull. The flatter and larger head of the hybrid, and especially the thick bill with a pronounced angle on the bottom, should help distinguish it from the smaller, slimmer Thayer's Gull.
- The Yellow-footed Gull of the Gulf of California formerly was regarded as a race of the Western Gull. But its legs are a different color, and it also takes only three, not four, years to reach adult plumage.
- 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.
- The oldest recorded Western Gull was at least 33 years, 11 months old. It was banded in 1973 in California, and sighted in the same state in 2007 and identified by its band.
- Breeds on rocky islands.
- Forages at sea, in intertidal areas, along beaches, and at dumps.
- Roosts in fields, dumps, and parking lots.
Marine invertebrates and fishes. Eggs and chicks of seabirds. Scavenges carrion and refuse.
- Clutch Size
- 1–3 eggs
- Egg Description
- Light buff or greenish with dark blotching.
- Condition at Hatching
- Chicks semiprecocial at hatching; may leave nest cup at one day old. Covered in cryptically colored down.
Nest is a scrape in the ground filled with vegetation, feathers, rope, plastic, or other items. Nests in colonies, often with other gull species.
Captures food near surface of water or on shore. Steals food from cormorants and other gulls. Swallows large prey whole. Common at garbage dumps.
Although still common, Western Gull numbers declined from 1966 to 2015, particularly in the Northwest, according to the North American Breeding Bird Survey. This may be a result from the increased frequency of El Niño years that decrease or eliminate nest success. The North American Waterbird Conservation Plan estimates over 77,000 breeding birds in North America. Western Gull rates a 13 out of 20 on the Continental Concern Score, and is not listed on the 2016 State of North America's Birds' Watch List. However, because of its small population size and limited range, the species should be monitored.
- Pierotti, R. J., and C. A. Annett. 1995. Western Gull (Larus occidentalis). In The Birds of North America, No. 174 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.
- Kushlan, J.A., et al. 2002. Waterbird conservation for the Americas: the North American Waterbird Conservation Plan, version 1. Waterbird Conservation for the Americas. Washington, DC.
- North American Bird Conservation Initiative. 2016. The State of North America’s Birds 2016. Environment and Climate Change Canada: Ottawa, Ontario.
- USGS Patuxent Wildlife Research Center. 2016. Longevity records of North American Birds.
- Sauer, J.R., J.E. Hines, J.E. Fallon, K.L. Pardieck, D.J. Ziolkowski, Jr., and W.A. Link. 2016. The North American Breeding Bird Survey, Results and Analysis 1966–2015, Version 01.30.2015. USGS Patuxent Wildlife Research Center, Laurel, MD.