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 global population to number 600,000 individuals. This roughly equates to 400,000 mature individuals.
The population is suspected to be in decline owing to unsustainable levels of egg-harvesting at its nesting colonies (del Hoyo et al. 1996).
White-cheeked Tern ranges from the Red Sea (seasonal breeding) south to Somalia and Kenya (resident), to the Persian Gulf and Oman (seasonal breeding) and locally to western India (resident). Seasonally breeding birds winter from the Arabian Sea to south-west Indian and the Laccadives (del Hoyo et al. 1996).
Behaviour The species is mostly migratory, although individuals breeding in East African may remain in their breeding range throughout the year (del Hoyo et al. 1996, Snow and Perrins 1998). It breeds with other tern species in well-dispersed colonies of 10-200 pairs (sometimes up to 900 pairs) and remains gregarious throughout the year (del Hoyo et al. 1996, Snow and Perrins 1998).
Habitat The species inhabits tropical coasts and inshore waters, foraging mainly within 3 km of land over coral reefs or occasionally up to 10 km offshore (del Hoyo et al. 1996). It nests on rock, sand, gravel or coral islands, bare and exposed sandflats and sparsely vegetated open ground on sand-dunes and above the high-water mark on beaches (del Hoyo et al. 1996, Snow and Perrins 1998).
Diet Its diet consists of small fish (average 5 cm long) and invertebrates (del Hoyo et al. 1996).
Breeding site The nest is a shallow scrape on rock, sand, gravel or coral in barren or sparsely vegetated areas on islands, sandflats, sand-dunes and beaches (del Hoyo et al. 1996, Snow and Perrins 1998).
Egg collection is believed to have caused rapid declines in a number of breeding colonies, with the population on Sheedvar Island (Iran) noted as falling from around 300,000 pairs in 1972 to fewer than 30,000 in 1977 (BirdLife International 2018). Egg collecting is believed to continue, but at a reduced rate as the market for eggs reduces (Jennings 2010). In India, the species has previously been found to be contaminated with PCB at levels which may affect embryo development (Kunisue et al. 2003).
Text account compilers
Malpas, L., Martin, R., Stuart, A., Ekstrom, J., Calvert, R., Butchart, S., Everest, J.
BirdLife International (2020) Species factsheet: Sterna repressa. Downloaded from http://www.birdlife.org on 25/09/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 25/09/2020.