Justification of Red List Category
This species has an extremely 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 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.
In Europe, the breeding population is estimated to number c.20,000 breeding pairs, equating to c.40,000 mature individuals (BirdLife International 2015). Europe forms approximately 10% of the global range, so a very preliminary estimate of the global population size is c. 400,000 mature individuals, although further validation of this estimate is needed. National population estimates include: c.1,000 individuals on migration in Taiwan (China); c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in Korea; c.50-10,000 wintering individuals in Japan and c.100-100,000 breeding pairs and c.50-10,000 individuals on migration in Russia (Brazil 2009).
The population is suspected to be stable in the absence of evidence for any declines or substantial threats. The European population trend is unknown (BirdLife International 2015).
This species breeds in the far north of Eurasia and North America. It is a transequatorial migrant, mostly wintering between the Tropic of Cancer and Tropic of Capricorn and along the coastlines of Australia and Argentina (del Hoyo et al. 1996).
This species is marine outside the breeding season, remaining somewhat coastal, especially in upwelling regions of the tropics and subtropics. Whilst breeding, it specialises on catching lemmings, which frequently constitute over 90% of their diet. It also feeds on young waders and gamebirds, bird eggs and carrion. In winter, it takes fish, sometimes by kleptoparasitism, small seabirds, and carrion. Breeding begins in June at scattered sites across the tundra where lemming concentrations are high. Individuals are highly territorial. Outside the breeding season, it migrates south, including long migrations over land (del Hoyo et al. 1996).
The productivity of this species is thought to fluctuate in accordance with changes in the population of lemmings, a key prey item during the breeding season (Maher 1974). As a result of this, it is expected that future changes to lemming populations driven by climate change may have impacts on the breeding success of the Pomarine Jaeger, with some declines already identified (Gily et al. 2009). The future impact on populations is unknown, but it has the potential to have a significant negative effect on productivity, that if continued over several years could begin to drive a decline in population level.
Conservation Actions Underway
The following information refers to the species's European range only: There are currently no known significant conservation measures for this species.
Conservation Actions Proposed
The following information refers to the species's European range only: No conservation measures are currently thought to be required for this species.
Text account compilers
Calvert, R., Butchart, S., Ashpole, J, Bennett, S., Ekstrom, J., Martin, R., Stuart, A.
BirdLife International (2019) Species factsheet: Stercorarius pomarinus. Downloaded from http://www.birdlife.org on 11/11/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 11/11/2019.