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. The species is named after Adolphus Lewis Heermann, nineteenth-century explorer and naturalist.left|thumb|Adult and fledgling by Roberts Lake in Seaside, California.The only known active breeding colony of Heermann's gull in the continental United States is located in Seaside, California, when a small number of gulls were observed nesting on artificial fill islands on Roberts Lake as of 1999. After the islands eroded away by 2007, the colony continued to nest on nearby rooftops. In June 2018, one of the colony's main nesting sites, the Seaside McDonald's, was destroyed by a drunk driving crash. In April 2019, after obtaining a permit from the City of Seaside, the Monterey Audubon Society deployed a floating artificial nesting island in Roberts Lake in an effort to restore nesting territory to the colony.

Diet

Heermann's gull eats small fish, marine invertebrates, lizards, insects, refuse, and carrion.

Behavior

This species nests colonially on the ground, like many gulls. The nests are often at densities as high as 110 nests per . 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

Isla Rasa was declared a sanctuary in 1964. 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".

  • Images and movies of Heermann's gull (Larus heermanni) at ARKive