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 may be moderately small to large, but it is not believed to 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 population is estimated to number 10,000-28,000 individuals, roughly equating to 6,700-19,000 mature individuals.
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).
This species is known from colonies around the coasts of southern Chile and Argentina, Tierra de Fuego, and the Falklands Islands (Islas Malvinas). Colonies are numerous along the South American coast, but tend to be very small, rarely exceeding 200 pairs (del Hoyo et al. 1996). In Argentina, the total population has been estimated at c.700 pairs. On the Falklands, there are 3,000-6,000 pairs which are widely distributed in small colonies (Woods and Woods 1997).
This species can be found on rocky coasts, feeding mainly on carrion, offal, bird eggs and chicks, but will also take marine invertebrates and other natural food. It scavenges around marine mammals for dead fish, placentae and particularly faeces. It exploits human intrusion into colonies by preying on unguarded eggs and chicks. It probes seaweed, captures swarming beach flies and will pick mussels which are then dropped onto rocks. It does not frequent rubbish dumps but will sometimes feed at sewage outlets. Colony attendance begins in September laying highly asynchronous broods. Colonies are small, with a maximum of 210 pairs recorded, and can be found on low sea cliffs, sand or gravel beaches, marshy depressions or headlands, usually in the vicinity of seabird colonies, marine mammals, slaughterhouses, sewers or farmyards (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., Harding, M., Ekstrom, J., Calvert, R.
BirdLife International (2019) Species factsheet: Larus scoresbii. Downloaded from http://www.birdlife.org on 23/10/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 23/10/2019.