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Least Tern Sternula antillarum

Justification
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). 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.

Taxonomic source(s)
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.
SACC. 2006. A classification of the bird species of South America. Available at: #http://www.museum.lsu.edu/~Remsen/SACCBaseline.html#.

Taxonomic note
Sternula antillarum (del Hoyo and Collar 2014) was previously placed in the genus Sterna.

Synonym(s)
Sterna antillarum (Lesson, 1847), Sternula antillarum AOU checklist (1998 + supplements)

Distribution and population
The Least Tern breeds along almost the entire coast of North America, excluding Alaska and Canada, on the northern coast of Central America and locally on the northern coast of South America. It also breeds inland along rivers in central North America. It is migratory, wintering on the southern coast of Central America, and the northern and Atlantic coast of South America as far south as central Brazil (del Hoyo et al. 1996).

Trend justification
The overall population trend is decreasing, although some populations are increasing or have unknown trends (Wetlands International 2006). This species has undergone a small or statistically insignificant decrease over the last 40 years in North America (data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007).

Ecology
This species can be found on lakes, rivers and estuaries, strictly on the coast in some regions (e.g. California) but inland in others (e.g. Florida). It feeds on small fish fry, shrimps, marine worms and occasionally flying ants and other insects. Prey are usually caught by plunge-diving up to 10m, preceeded by prolonged hovering, and it also occasionally peforms surface-dipping and aerial hawking. The breeding season begins between April and mid-June depending on locality, and it breeds in a large variety of habitats, from baren sandy beaches to parking lots and roof tops. Individuals form colonies usually between 5 and 200 pairs strong. It is a highly migratory species, though some populations in the north of South America, and on the Pacific coast of Mexico may be year-round residents (del Hoyo et al. 1996).

Related state of the world's birds case studies

References
del Hoyo, J.; Elliott, A.; Sargatal, J. 1996. Handbook of the Birds of the World, vol. 3: Hoatzin to Auks. Lynx Edicions, Barcelona, Spain.

Delany, S.; Scott, D. 2006. Waterbird population estimates. Wetlands International, Wageningen, The Netherlands.

Further web sources of information
Explore HBW Alive for further information on this species

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Ekstrom, J., Butchart, S., Calvert, R.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2014) Species factsheet: Sternula antillarum. Downloaded from http://www.birdlife.org on 22/11/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/11/2014.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Key facts
Current IUCN Red List category Least Concern
Family Laridae (Gulls, Terns, Skimmers)
Species name author (Lesson, 1847)
Population size mature individuals
Population trend Decreasing
Distribution size (breeding/resident) 1,340,000 km2
Country endemic? No
Links to further information
- Additional Information on this species