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). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to 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.
Delany and Scott (2006) estimate the population to be 150,000-300,000 individuals.
Although Wetlands International consider the population to be increasing, the population is suspected to be in decline owing to unsustainable levels of exploitation (del Hoyo et al. 1996).
The Sooty Gull can be found in the Red Sea and Gulf of Aden, in the Persian Gulf and Gulf of Oman, east to south Pakistan and south to northern Kenya (Kiunga Islands) (del Hoyo et al. 1996).
Behaviour This species is a partial migrant or nomad (Urban et al. 1986), most populations undergoing southern post-breeding dispersal movements (Urban et al. 1986, del Hoyo et al. 1996) in September-November (Olsen and Larsson 2003). Some populations may also be sedentary (many remain in the Red Sea area all year round) (del Hoyo et al. 1996). The species breeds in the Summer (usually between April and October; Olsen and Larsson 2003), and usually nests colonially (e.g. in small loose colonies on the larger islands in the Gulf of Aden and Red Sea), or occasionally solitarily (e.g. in Africa), with 1-3 pairs per island often amidst colonies of other species (Urban et al. 1986, del Hoyo et al. 1996). It usually forages alone, but is highly gregarious at times (del Hoyo et al. 1996). Habitat The species inhabits coasts and inshore islands and is hardly ever seen inland (Urban et al. 1986, del Hoyo et al. 1996) or at freshwater (Cramp and Simmons 1983). It is found at harbours and ports, and forages inshore, in intertidal zones (Urban et al. 1986, del Hoyo et al. 1996), and up to 10 km beyond reefs (Urban et al. 1986), rarely extending up to 140 km offshore (Cramp and Simmons 1983, del Hoyo et al. 1996). It nests on coastal or inshore coral islands preferring smaller outer islands of old coral that are sparsely vegetated, rocky and sandy, preferably protected from the ocean by live reef (Cramp and Simmons 1983). Diet Its diet consists mainly of dead fish and fishermen's offal, as well as tern eggs and chicks (Urban et al. 1986, del Hoyo et al. 1996), the eggs of White-eyed Gull Larus leucophthalmus (Urban et al. 1986), turtle hatchlings (Urban et al. 1986, del Hoyo et al. 1996), prawns and small fish (Cramp and Simmons 1983). It poses a threat to other species as it is a serious local predator of eggs and chicks in colonies of other seabirds (Gallagher et al. 1984). Breeding site The nest is a scrape or depression in bare coral (Kenya) (Cramp and Simmons 1983, Urban et al. 1986, del Hoyo et al. 1996), under mangrove bushes on a bed of leaves, under Suaeda bushes in loose sand (Somalia) (Cramp and Simmons 1983, Urban et al. 1986), or under low hanging coral (Red Sea) (Cramp and Simmons 1983, del Hoyo et al. 1996) on exposed promontories (Urban et al. 1986).
The Sooty Gull is vulnerable to oil spills (Javed et al. 2005) and is at risk of habitat degradation due to land reclamation for oil prospecting in the Gulf region (Javed et al. 2005) as well as disturbance to breeding birds from future oil drilling in Tanzania (Cooper et al. 1984). The main predation pressure on this species likely comes from humans, with nests in Astola Island, Pakistan, regularly robbed of eggs, and a reduction in the number of breeding birds in the Seychelles due to egg collection for human consumption (Blackburn and Bird 2013).
Text account compilers
Butchart, S., Calvert, R., Malpas, L., Martin, R., Ekstrom, J., Palmer-Newton, A., Stuart, A.
BirdLife International (2019) Species factsheet: Larus hemprichii. Downloaded from http://www.birdlife.org on 20/11/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 20/11/2019.