LC
Sandwich Tern Thalasseus sandvicensis



Justification

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 fluctuating, 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.

Population justification
The global population is estimated at 490,000-640,000 individuals (Wetlands International 2015). Within this, the European population is estimated at 79,900-148,000 pairs, which equates to 160,000-295,000 mature individuals (BirdLife International 2015).

Trend justification
The overall population trend is fluctuating, although some populations are stable, others have unknown trends (Wetlands International 2015). This species has undergone a small or statistically insignificant increase over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). Note, however, that these surveys cover less than 50% of the species's range in North America. The European population is also estimated to be fluctuating (BirdLife International 2015).

Distribution and population

This species can be found in Europe, Africa, western Asia, and the southern Americas. It breeds seasonally on the coast of much of Europe east to the Caspian Sea, wintering from the Caspian, Black and Mediterranean Seas to the coasts of western and southern Africa, and from the south Red Sea to north-west India and Sri Lanka. In the Americas, it breeds from Virginia to Texas (U.S.A.), on the coasts of the Yucatan Peninsula, Lesser Antilles, Venezuela, French Guiana, eastern Brazil and Argentina. It winters from Texas, USA down to southern Argentina, in the Greater Antilles and from southern Mexico down to northern Chile (del Hoyo et al. 1996).

Ecology

Behaviour This species is migratory, undergoing post-breeding dispersive movements north and south to favoured feeding grounds before migrating southward (del Hoyo et al. 1996). It breeds in dense colonies with other terns or Black-headed Gulls Larus ridibundus (del Hoyo et al. 1996) and is gregarious throughout the year, often forming feeding flocks where prey is abundant or concentrated (although it may also feed solitarily) (Snow and Perrins 1998). Habitat Breeding During the breeding season the species forms colonies on sandy islands, rocky calcareous islets, sand-spits, sand-dunes, shingle beaches and extensive deltas with immediate access to clear waters with shallow sandy substrates rich in surface-level fish (Snow and Perrins 1998). It shows a preference for raised, open, unvegetated sand, gravel, mud or bare coral substrates for nesting (del Hoyo et al. 1996). Non-breeding Outside of the breeding season the species frequents sandy or rocky beaches, mudflats fringed by mangroves, estuaries, harbours and bays, often feeding over inlets and at sea (del Hoyo et al. 1996). Diet Its diet consists predominantly of surface-dwelling marine fish 9-15 cm long as well as small shrimps, marine worms and shorebird nestlings (del Hoyo et al. 1996; Snow and Perrins 1998). Breeding site The nest is a shallow scrape on raised, open, unvegetated sand, gravel, mud or bare coral substrates preferably far from upright vegetation (del Hoyo et al. 1996) on sandy islands, rocky calcareous islets, sand-spits, sand-dunes and shingle beaches (Snow and Perrins 1998). The species forms very dense colonies during the breeding season in which the eggs of neighbouring pairs may only be 20 cm apart (del Hoyo et al. 1996). Management information The species responds favourably to habitat management such as vegetation clearance, and can be readily attracted to suitable nesting habitats by the use of decoys (del Hoyo et al. 1996). Breeding pairs are also known to be attracted to coastal locations where artificial nesting sites have been constructed (e.g. beaches of bare shingle and islands or rafts covered with sparse vegetation) (Burgess and Hirons 1992). A conservation scheme for the protection of gull and tern breeding colonies in coastal lagoons and deltas (e.g. Po Delta, Italy) involves protection from human disturbance, prevention of erosion of islet complexes, habitat maintenance and the creation of new islets for nest sites (Fasola and Canova 1996). The scheme particularly specifies that bare islets with 30-100 % cover of low vegetation (sward heights less than 20 cm) should be maintained or created as nesting sites (Fasola and Canova 1996).

Threats

As only a few colonies exist each year, this tern is highly vulnerable to anthropogenic disturbance (Garthe and Flore 2007) and is known to abandon eggs en masse (Gochfield et al. 2018). This species has also suffered declines due to egging and hunting, which are locally significant in some areas of its range (Gochfield et al. 2018).

Conservation actions

Conservation Actions Underway
The following information refers to the species's European range only: CMS Appendix II. EU Birds Directive Annex I. Bern Convention Appendix II. A conservation scheme for the protection of gull and tern breeding colonies in coastal lagoons and deltas (Po Delta, Italy) involves protection from human disturbance, prevention of erosion of islet complexes, habitat maintenance and the creation of new islets for nest sites (Fasola and Canova 1996). The scheme particularly specifies that bare islets with 30-100% cover of low vegetation (sward heights less than 20 cm) should be maintained or created as nesting sites (Fasola and Canova 1996).

Conservation Actions Proposed
The following information refers to the species's European range only: The species responds favourably to habitat management such as vegetation clearance, and can be readily attracted to suitable nesting habitats by the use of decoys (del Hoyo et al. 1996). Breeding pairs are also known to be attracted to coastal locations where artificial nesting sites have been constructed (e.g. beaches of bare shingle and islands or rafts covered with sparse vegetation) (Burgess and Hirons 1992).

Acknowledgements

Text account compilers
Calvert, R., Butchart, S., Ekstrom, J., Ashpole, J, Malpas, L., Martin, R., Stuart, A.


Recommended citation
BirdLife International (2019) Species factsheet: Thalasseus sandvicensis. Downloaded from http://www.birdlife.org on 15/10/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 15/10/2019.