Heermann's gull

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Heermann's gull
Larus heermanni13.JPG
Adult breeding
Heermann's Gull winter plumage.jpg
Adult non-breeding
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Charadriiformes
Family: Laridae
Genus: Larus
Species: L. heermanni
Binomial name
Larus heermanni
Cassin, 1852, San Diego, California
Larus heermanni distr.png

The Heermann's gull (Larus heermanni) is a gull resident in the United States, Mexico and extreme southwestern British Columbia, nearly all nesting on Isla Rasa in the Gulf of California. They are usually found near shores or well out to sea, very rarely inland.

Description[edit]

This species looks distinctly different from other gulls. Adults have a medium gray body, blackish-gray wings and tail with white edges, and a red bill with a black tip. The head is dusky gray in non-breeding plumage and white in breeding plumage. Immatures resemble non-breeding adults but are darker and browner, and the bill is flesh-colored or pink till the second winter. A few birds, no more than 1 in 200, have white primary coverts, which form a showy spot on the upper wing. This gull is unlikely to be confused with other species as it is the only white-headed, gray-bodied gull found on the west coast of North America.[2]

Calls are described as deep and similar in pattern to other gulls but noticeably different in quality.

Distribution[edit]

in Bahia de Kino, Sonora, Mexico

Of the current population of about 150,000 pairs, 90% nest on the island of Isla Rasa off Baja California in the Gulf of California, with smaller colonies as far north as California and as far south as Nayarit. After breeding, birds commonly disperse to central California, and less commonly north as far as British Columbia and south as far as Guatemala.[1]

Behavior[edit]

This species nests colonially on the ground, like many gulls. The nests are often at densities as high as 110 nests per 100 square metres (1,100 sq ft). It lays two or three eggs, grayish buff, to buff with gray and brown markings.

Heermann's gull sometimes steals prey from other seabirds, particularly brown pelicans, with which it often associates.

Status[edit]

Isla Rasa was declared a sanctuary in 1964, and egg-collecting and disturbance during the breeding season are discouraged. With the breeding colony concentrated on one small island this species is vulnerable to a catastrophic weather event. The success of the colony in any one year is dependent on the availability of prey and this is related to the ocean temperature changes brought about by El Niño. These factors have caused the IUCN to rate this bird as "Near Threatened".[1]

References[edit]

  1. ^ a b c BirdLife International (2012). "Larus heermanni". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ "Heermann's Gull". Cornell Lab of Ornithology. Retrieved 2013-12-13. 
  • Steve N. G. Howell and Sophie Webb (1995). A Guide to the Birds of Mexico and Northern Central America. Oxford University Press. ISBN 0-19-854012-4. 
  • David Sibley (2000). The Sibley Guide to Birds. Knopf. ISBN 0-679-45122-6. 

External links[edit]