Heermann's Gull Life History

Habitat

Habitat Shorelines

Heermann’s Gulls nest mostly on a rocky volcanic island in the Gulf of California (Sea of Cortez) called Isla Rasa, Mexico, which has little vegetation other than cholla cactus, saltbush, glasswort, and other desert-adapted plants. A few pairs also nest in California on dredge-spoil islands and rooftops. They forage in both nearshore (littoral) ocean waters and farther offshore, as they search for schools of small fish. Mostly, they forage within 10 miles of land. Here they mix with other coastal seabirds in large feeding flocks. Heermann’s Gulls also forage and scavenge in kelp beds, in tidepools, on beaches, and in protected harbors, sloughs, lagoons, and estuaries near the ocean. They rest and roost on beaches, rocks, pilings, piers, and other human-made sites along the coast.

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Food

Food Fish

Like other gulls, Heermann’s are omnivores, readily consuming many kinds of marine animals as well as carrion, eggs (especially of terns), insects, and small terrestrial vertebrates such as lizards. While at sea, they capture most prey by dipping the head into the water, either in flight or when resting on the water. Sometimes they plunge deeply, submerging the whole body in pursuit of food. On land, or on kelp beds, they pick or glean food from the surface with the bill. Heermann’s Gulls often pirate meals from other seabirds, especially Brown Pelicans. Several gulls will mob a pelican that has a pouch full of fish, sometimes forcing the larger bird to lose some of the contents of its pouch, which the gulls quickly seize. They also steal fish from smaller gulls, terns, and from boobies, sometimes after long chases. Main prey include Pacific sardine, northern anchovy, herring, smelt, small crustaceans (amphipods), mollusks, shrimp, and squid.

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Nesting

Nest Placement

Nest Ground

Nests on islands, on the ground in rocky or grassy sites.

Nest Description

Nest is a scrape on the ground (9–14 inches across), lined with debris such as feathers, grasses, sticks, flotsam, or shells.

Nesting Facts

Clutch Size:1-3 eggs
Egg Description:

Pale bluish gray to olive, with brown blotches.

Condition at Hatching:

Semiprecocial with eyes open. Covered in down, grayish white mottled with dusky on back, pinkish buff on head and underparts.

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Behavior

Behavior Ground Forager

Heermann’s Gulls are probably monogamous in their mating system, with both parents sharing incubation and chick-feeding duties. Males court females by flying over them, calling, and females respond by "groveling": hunching down and giving squeaky call notes that sound like begging young. Males perform courtship feeding in response and often continue to feed their mates each time they swap places during incubation. Some pairs touch and even lock bills during courtship. On the breeding grounds, Heermann’s Gulls are highly gregarious, nesting near others of their species but typically away from larger species such as Yellow-footed Gulls and away from terns. After the breeding season, they disperse mostly northward toward the United States, where they form small flocks that often rest among other seabirds, especially gulls and terns.

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Conservation

Conservation Restricted Range

Heermann's Gulls are numerous, but their population trends are unknown. Partners in Flight estimates the global breeding population at 350,000, up from a 1975 estimate of just 55,000 pairs. Even so, Partners in Flight rates the species a 16 out of 20 on the Continental Concern Score and includes it on the Yellow Watch List for species with restricted ranges. Historically, thousands of Heermann's Gull eggs were harvested each year at Isla Rasa, Mexico, their main breeding colony. The island was made a protected bird sanctuary in 1964. Among the most concerning present threats to this species are introduced black rats on their nesting island, overharvest of anchovy and sardine by commercial fishing interests, and changing distributions and abundance of prey species as a result of climate change.

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Credits

Islam, Kamal. (2002). Heermann's Gull (Larus heermanni), 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.

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

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