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 stable, 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 extremely 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.1,100,000 individuals (Dlany and Scott 2006), while national population estimates include: c.100-100,000 breeding pairs and c.50-10,000 wintering individuals in China; c.50-1,000 wintering individuals, c.1,000-10,000 individuals on migration and < c.100 breeding pairs in Taiwan; c.10,000-100,000 breeding pairs in Korea; c.10,000-100,000 breeding pairs in Japan and c.10,000-100,000 breeding pairs and c.1,000-10,000 individuals on migration in Russia (Brazil 2009).
Although Wetlands International consider the current population trend to be unknown, it is suspected to be stable in the absence of evidence for any declines or substantial threats (del Hoyo et al. 1996).
The Black-tailed Gull is found in east Asia, specifically the coasts of eastern China, Japan, North Korea, South Korea and Sakhalin, Russia (del Hoyo et al. 1996).
This species is found on coasts, and in bays and estuaries. Its diet varies locally and annually, but includes small fish, crustaceans, insects, offal, molluscs and polychaetes. It often follows fishing boats and can be a kleptoparasite. Colonies form mid-April on sandy or rocky seashores, sea cliffs and rocky islets. Many colonies hold over 10,000 pairs. Post-breeding it moves to areas rich in food (del Hoyo et al. 1996).
At present there are no factors thought to pose a genuine threat to this species.
Text account compilers
Ekstrom, J., Calvert, R., Butchart, S.
BirdLife International (2019) Species factsheet: Larus crassirostris. Downloaded from http://www.birdlife.org on 19/04/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 19/04/2019.