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LC
Royal Tern Thalasseus maximus

Justification
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). 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.

Taxonomic source(s)
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: #http://www.aerc.eu/DOCS/Bird_taxa_of _the_WP15.xls#.
Cramp, S.; Perrins, C. M. 1977-1994. Handbook of the birds of Europe, the Middle East and Africa. The birds of the western Palearctic. Oxford University Press, Oxford.
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
Thalasseus maximus (del Hoyo and Collar 2014) was previously placed in the genus Sterna as S. maxima.

Synonym(s)
Sterna maxima Boddaert, 1783, Thalasseus maximus AOU checklist (1998 + supplements), Thalasseus maximus Stotz et al. (1996)

Distribution and population
The Royal Tern is found in the Americas and the Atlantic coast of Africa. In Africa is breed from Mauritania to Guinea, ranging in winter from Morocco to Namibia. In the Americas it breeds from southern California (USA) to Sinaloa (Mexico), from Maryland to Texas (USA), through the West Indies to the Guianas and possibly Brazil, on the Yucatan Peninsula, in south Brazil, Uruguay and north Patagonia (Argentina). It winters from Washington (USA) south to Peru on the western coast, and from Texas to south Brazil on the eastern side (del Hoyo et al. 1996).

Trend justification
The overall population trend is stable, although some populations have unknown trends (Wetlands International 2006). 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.

Ecology
Behaviour This species undergoes post-breeding dispersive movements northwards before migrating southwards for the winter (del Hoyo et al. 1996). It breeds between April and June (Richards 1990) in dense colonies of 100-4,000 pairs often near colonies of Laughing Gull Larus atricilla and Sandwich Tern Sterna sandvicensis (del Hoyo et al. 1996). The species may also nest singly amidst colonies of other tern species (del Hoyo et al. 1996). It usually feeds singly or in small flocks and roosts gregariously even outside of the breeding season (del Hoyo et al. 1996). Habitat Breeding For breeding the species shows a preference for inaccessible sites including barren sandy beaches, islands in saltmarsh, dredge spoil and coral islands surrounded by shallow water and with a high degree of visibility, no mammalian predators and little vegetation (del Hoyo et al. 1996). It also forages along estuaries, in lagoons and in mangroves during this season, mostly within 100 m of the shore but up to 40 km from the breeding colony (del Hoyo et al. 1996). Non-breeding Outside of the breeding season the species forages within 100 m of the land along sheltered coasts in estuaries, harbours and river mouths, sometimes also foraging a short distance inland along broad rivers (del Hoyo et al. 1996). Diet Its diet consists predominantly of small fish 3-18 cm long as well as squid, shrimps and crabs (del Hoyo et al. 1996). Breeding site The nest is a simple scrape (del Hoyo et al. 1996) in sand (Urban et al. 1986) in inaccessible sites surrounded by shallow water near the mouths of bays with a high degree of visibility, no mammalian predators and little vegetation (del Hoyo et al. 1996). Management information The preferred breeding sites of this species are often vulnerable to flooding (del Hoyo et al. 1996).

Threats
The species is potentially threatened by the contamination of large prey with pesticides (through bioaccumulation in the food chain) (del Hoyo et al. 1996). It has also suffered dramatic declines over the past 25 years in California due to the disappearance of its staple prey (the Pacific sardine) through overfishing (del Hoyo et al. 1996). Utilisation Egg-collecting is known to occur at breeding colonies of this species (del Hoyo et al. 1996, Del Viejo et al. 2004).

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.

Del Viejo, A. M.; Vega, X.; Gonzalez, M. A.; Sanchez, J. M. 2004. Disturbance sources, human predation and reproductive success of seabirds in tropical coastal ecosystems of Sinaloa State, Mexico. Bird Conservation International 14(3): 191-202.

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

Richards, A. 1990. Seabirds of the northern hemisphere. Dragon's World Ltd, Limpsfield, U.K.

Urban, E. K.; Fry, C. H.; Keith, S. 1986. The birds of Africa vol. II. Academic Press, London.

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
Calvert, R., Malpas, L., Butchart, S., Ekstrom, J.

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

Recommended citation
BirdLife International (2014) Species factsheet: Thalasseus maximus. Downloaded from http://www.birdlife.org on 01/08/2014. Recommended citation for factsheets for more than one species: BirdLife International (2014) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 01/08/2014.

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 Boddaert, 1783
Population size mature individuals
Population trend Stable
Distribution size (breeding/resident) 983,000 km2
Country endemic? No
Links to further information
- Additional Information on this species
- Projected distributions under climate change