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Western Gull Life History

Habitat

Habitat Oceans

Western Gulls nest only in places free from disturbance and isolated from predators such as foxes and coyotes: islands, headlands, and abandoned seaside structures such as piers or old buildings. They nest on the ground, particularly where short plants or rocky terrain provide cover for the nest. Western Gulls often forage along coastlines near nesting areas but sometimes make long commutes to locations rich in prey. Year-round, they forage out at sea and along rocky or sandy shores exposed by the tide. Like other large gull species, they are attracted to garbage dumps, fishing boats, and fish-processing plants. In many places, they linger around restaurants and picnic tables, hoping for a handout. When resting, Western Gulls form flocks in parking lots, ball fields, and beaches.

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Food

Food Fish

Like many gulls, Western Gulls are omnivores and opportunistic. They prey mostly on fish and marine invertebrates, mostly in the intertidal zone and adjacent ocean waters, where they have a remarkable repertoire of foraging techniques. When hunting in intertidal areas, they swim or walk along, watching for invertebrates or fish, which they capture by pouncing, plunging, or diving shallowly. Depending on the type of prey, they may swallow it whole, dismember it, or even (for hard-shelled creatures such as oysters, clams, and crabs) fly up high into the air and drop it on rocks or pavement to break open the shell. With prey items that cling to rocks or flotsam, such as barnacles, they seize them with the bill and rip them off. At lower tides, they hunt starfish, sea urchins, fish, and other marine creatures in tidepools.

Western Gulls also eat fish spawn along coastlines, swimming, dipping, and plunging to reach it, and hunt invertebrates in kelp beds using similar methods. In offshore waters, they often follow marine mammals (dolphins, seals, sea lions) in searching for concentrations of prey. They also join large mixed-species flocks of seabirds (pelicans, cormorants, murres, auklets, shearwaters, kittiwakes), where they often steal prey items from other species but also capture prey themselves by hovering briefly and dipping from the water, landing on the water, or even diving shallowly.

As in other seabirds, Western Gulls gather around fishing boats and frequent areas such as seamounts, where upwelling currents bring nutrients and thus prey species to the surface. On land, they eat adult birds, including auklets and storm-petrels, and bird eggs and nestlings. They also scavenge carrion (mammals, fish, and marine invertebrates) on beaches and eat placenta in sea lion rookeries. They frequent dumps and landfills only when natural food is in short supply. Prey include opalescent inshore squid, gooseneck barnacle, squat lobsters, pelagic red crab (and many other kinds of crab), tiny shrimplike crustaceans (euphausiids), purple sea urchins, clams, cockles, snails, limpets, mussels and many kinds of fish—including northern anchovy, Pacific whiting, jack mackerel, jacksmelt, Pacific saury, Pacific sandlance, white croaker, surfperch, spotted cusk eel, candlefish, and various species of rockfish and midshipman. On rare occasions, they eat small mammals such as rabbits.

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Nesting

Nest Placement

Nest Cliff

Nests are set in sheltered spots on the ground, usually on islands, offshore rocks, or abandoned piers safe from terrestrial predators and disturbance.

Nest Description

Both male and female make a scrape in the ground, often next to a windbreak (log, bush, rock). They line the scrape with weeds, grasses, seaweed, feathers, and jetsam. Nests measure around 11.8 inches across, with interior bowl 5.9 inches across and 2.4 inches deep.

Nesting Facts

Clutch Size:1-3 eggs
Egg Description:Light buff or greenish with dark blotching.
Condition at Hatching:

Alert; may leave nest cup at one day old. Covered in camouflaged down.

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Behavior

Behavior Ground Forager

Western Gulls have limited courtship displays in spring, and many pairs remain bonded for life. At the beginning of the nesting cycle, males establish territories and females solicit food from males by rapid upward movements of the bill, similar to a begging chick. Males respond with an upright posture, calling, and sometimes by regurgitating food. Once the nest site is established and eggs are laid, the pair greet each other by head-tossing, calling (with neck outstretched), and a display called “choking” (calling with head down, bill open, as though trying to swallow something large). They perform these displays when one parent relieves the other of incubation duties. Western Gulls are territorial around the nest, and both adults defend eggs and young. Males in particular perform a variety of displays to warn rivals away from the female and the nest. Males sometimes attempt to mate with paired females but the female or her mate usually fight off the attacker. Fights can be intense, involving powerful pecks, pulling feathers, and battering with the wings. In places where Western Gulls nest in mixed colonies with Glaucous-winged Gulls, Westerns are as aggressive toward them as they are toward other Western Gulls.

Both adults feed the young until they fledge, after which the young disperse to forage along shorelines. Paired adults sometimes remain together throughout the nonbreeding season and defend feeding territories along favored stretches of beach; others form large flocks to forage, rest, and roost.

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Conservation

Conservation Restricted Range

Western Gulls are common, but their restricted range and susceptibility to oil spills and climatic shifts (such as El Niño) make them a species of conservation concern. The North American Breeding Bird Survey estimates a likely decline in their numbers between 1968 and 2017. Reasons likely include lingering effects of DDT (not banned until 1972) and from an uptick in El Niño-Southern Oscillation (ENSO) events in the 1980s and 1990s, which lowered populations of the gulls' prey. Partners in Flight estimates the global breeding population of Western Gull at 86,000, of which an estimated 44,000 breed in the U.S. and Canada. The group rates the Western Gull a 14 out of 20 on the Continental Concern Score, and includes it on the Yellow Watch List for species with restricted ranges.

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Credits

Kushlan, J. A., M. J. Steinkamp, K. C. Parsons, J. Capp, M. A. Cruz, M. Coulter, I. Davidson, L. Dickson, N. Edelson, R. Elliott, R. M. Erwin, S. Hatch, S. Kress, R. Milko, S. Miller, K. Mills, R. Paul, R. Phillips, J. E. Saliva, W. Sydeman, J. Trapp, J. Wheeler and K. Wohl (2002). Waterbird conservation for the Americas: The North American waterbird conservation plan, version 1. Washington, DC, USA.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Pierotti, Raymond J. and Cynthia A. Annett. (1995). Western Gull (Larus occidentalis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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