WatchList Species Account for Heermann’s Gull (Larus Heernanni)

Qualifies for the list as a Rare Yellow List Species

Photo: © Glenn and Martha Vargas, California Academy of Sciences

Close to 95% of the entire world’s population of Heermann’s Gull nests in a single location: Isla Rasa, in the Gulf of California, Mexico, which supports 300,000 breeding birds. The island is protected by the Government of Mexico as a seabird sanctuary. The other nesting locations are islands along the coast of western Mexico; there are no sites where the species has successfully bred within the U.S. The bird undertakes a reverse migration, beginning in May, when non-breeders appear off the California coast, later to be joined by breeders. It moves as far north as Vancouver Island, British Columbia, before all but a few individuals head back south during the fall and winter.

The bird generally feeds on schools of herring several kilometers offshore. An aggressive bird, it often snatches fish from the pouches of Brown Pelicans. Once persecuted by Mexican fishermen who collected their eggs, the bird has been protected at its main nesting site for several years; the population has nearly tripled in the last 30 years. High concentrations of pesticides have been found in the gull, but it is now known if this has had an effect on reproductive success. Since the vast majority of this species nests at a single locality, any disruptions or environmental disasters there could significantly impact its population.