Justification of Red List Category
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
The global population is estimated to number > c.570,000 individuals (Delany and Scott 2006), while the population in Russia has been estimated at c.100-10,000 breeding pairs and c.50-1,000 individuals on migration (Brazil 2009).
The overall population trend is increasing (Delany and Scott 2006), although some populations are stable. This species has had stable population trends over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).
This species ranges from northern Mexico in the Gulf of California and on the western coast of Baja California, up the Pacific coast of North America to Alaska, across the Aleutian Islands (USA) to the northern coast of Japan. Its breeding range begins on the coast of Washington (USA), through Canada and Alaska to the Commander Islands (Russia) (del Hoyo et al. 1996)
This species can be found in coastal areas and over shelf waters. Its diet is comprised of fish, various marine invertebrates, carrion, offal, bird eggs and small mammals, with the exact composition varying depending on locality. It uses a variety of feeding methods, including plunge-diving, diving from the surface and dropping shellfish on rocks. It arrives at breeding colonies between February and March, and will nest on a wide variety of substrates including rocky islands, cliffs, inland lakes, city parks and buildings. It is usually colonial but can be solitary. Some birds remain on their territories over winter, but others will migrate to the southern edges of its range (del Hoyo et al. 1996).
At present there are no factors thought to pose a genuine threat to this species.
Text account compilers
Butchart, S., Calvert, R., Ekstrom, J.
BirdLife International (2019) Species factsheet: Larus glaucescens. Downloaded from http://www.birdlife.org on 19/09/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/09/2019.