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Glaucous-winged Gull Life History

Habitat

Habitat Shorelines

Most Glaucous-winged Gulls spend their lives very close to ocean shorelines, where they nest on offshore islands and even rooftops. They forage in coastal habitats, from muddy rivermouths and sheltered coves to sandy and rocky beaches of the outer coastline. They hunt in rocky tidepools during lower tides, finding prey trapped by the falling water level. They also gather at fish-processing factories, where they eat discarded parts of fish, and they follow fishing vessels to eat spilled or discarded fish. In some areas, they fly inland during higher tides to scavenge at landfills, returning to marine coastlines later to bathe and forage during lower tides.

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Food

Food Omnivore

Opportunistic and omnivorous, Glaucous-winged Gulls have a great array of foraging techniques and food items. When hunting in tidal areas, they swim or walk along, watching for invertebrates or fish, which they capture by pouncing, plunging, or even 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. For prey that cling to rocks, such as chiton, limpets, and barnacles, they seize them with the bill and rip them off. At lower tides, they hunt starfish, fish, and other marine creatures in tidepools. During the short spawning season of small fish such as Pacific herring, they often feed heavily and almost exclusively near shorelines on this small prey, which they capture by dipping and plunging. Likewise, they join mixed-species seabird flocks offshore when fish such as adult herring, capelin, or sandlance are concentrated. Glaucous-winged Gulls also hunt birds, including eggs and chicks (even of their own species), and small mammals such as rabbits. Where Bald Eagles or bears hunt salmon or larger animals, they scavenge the remains of the leftover kill. They readily forage for household food scraps in landfills as well.

Prey items include black chiton, lined chiton, shield limpet, plate limpet, purple sea urchin, Pacific blood star, blue mussel, California mussel, Pacific littleneck clam, acorn barnacle, thatched barnacle, gooseneck barnacle, dogwinkle, leafy hornmouth, various whelk species, purple shore crab, hairy helmet crab, northern kelp crab, Pacific saury, Pacific herring, capelin, Pacific sandlance, rock greenling, California anchovy, and birds such as Rock Pigeon, Leach’s Storm-Petrel, Fork-tailed Storm-Petrel, Least Auklet, and Ancient Murrelet.

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Nesting

Nest Placement

Nest Ground

Male and female look for a ground nest site together, usually selecting a spot on level rocky or grassy areas on treeless islands in the Pacific Ocean but near to shore. They sometimes nest on wharves, roofs, and other structures.

Nest Description

Both male and female create a nest scrape and build a rough-looking nest of grasses, weeds, moss, roots, dead twigs, string, and even bones. Nests average about 15.2 inches across, with interior depression about 8.5 inches across and 4.2 inches deep.

Nesting Facts

Clutch Size:1-4 eggs
Egg Description:

Light greenish marked with dark scrawls.

Condition at Hatching:

Chicks semiprecocial at hatching; may leave nest cup at one day old. Covered in cryptically colored down.

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Behavior

Behavior Ground Forager

Glaucous-winged Gulls begin courtship displays in spring. Some pairs remain bonded for several consecutive years, and the displays of these returning pairs are often abbreviated. Females at this time solicit food from males by flicking the bill upward, similar to a begging chick. Males respond by regurgitating food, usually fish and barnacles. Early in the nesting season, males and females may preen the head and neck feathers of their mates. Once the nest site is established and eggs are laid, the pair exchanges greetings of head-tossing, calling (with neck outstretched), and a display called “choking” (with head down, bill open, as though trying to swallow something large). They perform these displays whenever one parent relieves the other of incubation duties. Glaucous-winged Gulls are territorial around the nest, and both adults defend eggs and young. Males use calls and aggressive postures to warn rivals away from the female and the nest. On occasion, wandering males attempt to mate with paired females but are typically chased off by the female or attacked by her mate. Fights in this species, as in other large gulls, can be intense, involving powerful pecks, biting at wings and tails, and battering with wings.

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, but most adults forage, rest, and roost in groups, occasionally very large flocks.

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Conservation

Conservation Low Concern

According to the North American Breeding Bird Survey, Glaucous-winged Gull populations were roughly stable between 1968 and 2015. Partners in Flight estimates a global breeding population of 380,000 and rates the species a 12 out of 20 on the Continental Concern Score, indicating a species of low conservation concern. Threats to Glaucous-winged Gulls include changes in prey availability that may result from global climate change, and marine pollutants (including oil spills and pesticide pollution).

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Credits

Hayward, James L. and N. A. Verbeek. (2008). Glaucous-winged Gull (Larus glaucescens), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

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. (2019). Longevity records of North American birds. Version 1019 Patuxent Wildlife Research Center, Bird Banding Laboratory 2019.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

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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