Royal tern (Sterna maxima)

French: Sterne royale
KingdomAnimalia
PhylumChordata
ClassAves
OrderCharadriiformes
FamilyLaridae
GenusSterna (1)
SizeLength: 45 - 50 cm (2)
Wingspan: 125 - 135 cm (2)
Weight350 - 450 g (2)

The royal tern is classified as Least Concern (LC) on the IUCN Red List (1).

A large tern of the family Sternidae, the royal tern (Sterna maxima) is second only in size to the Caspian tern (3). It is considered to be one of six species of ‘crested’ tern, which, according to some taxonomists, should be grouped separately from the typical black-capped terns (Sterna) into the revised genus Thalasseus (2) (4).

The royal tern has a slender body, long, pointed wings and a notched tail (3). The upperparts and the rump are typically pale grey, while the underparts and tail are white (2) (3) (5) (6). The wings have a white trailing edge, and the primary feathers are white below, with dark trailing edges. The legs and feet are black (2). The wide, powerful, pointed bill is characteristically orange-red (2) (3) (7) (8). In breeding plumage, the royal tern has a black crown, as well as a distinctive shaggy black crest (2) (3) (6) (7) (8). In its basic plumage, the forehead and the area between the eyes and the bill become fully white, and the crown is streaked with white (2) (3) (6). The bill also turns somewhat paler during the non-breeding season (2). The black crest is retained year-round (2) (3) (6). 

The juvenile royal tern resembles the non-breeding adult, but has a smaller, paler, yellow bill, as well as a whiter crown, dark spots or blotches on the back, and darker tips to the wings (2) (3) (6). The flight feathers are dark, and a dark band is visible on the upper-wing. The tail of the juvenile royal tern is much duskier and shorter than the adults (2).

Two subspecies of the royal tern are recognised: Sterna maxima maxima which occurs in North and South America, and Sterna maxima albididorsalis from West Africa. Both subspecies are similar in appearance, although S. m. albididorsalis and south-eastern South American populations of S. m. maxima differ from North American populations of S. m. maxima in being smaller, slenderer and slightly paler, with a longer, thinner bill (2). 

The royal tern is found in North and South America, and on the Atlantic coast of Africa. In the Americas, the royal tern subspecies Sterna maxima maxima breeds from southern California to Mexico and the Yucatan Peninsula, on the Atlantic and Gulf coasts of North America and the Caribbean, and in south-eastern South America (2) (5) (6) (8) (9). It winters on the Pacific Coast, from Washington in the U.S. to Peru, and on the Atlantic coast, from Texas in the U.S., through the Caribbean to southern Brazil (5) (9) (10). 

In Africa, subspecies Sterna maxima albididorsalis breeds from Mauritania to Guinea on the western coast, ranging in winter from the Straits of Gibraltar and Morocco to Namibia (6) (9) (11) (12). The African subspecies of the royal tern may be vagrant in Europe (5).

A primarily coastal species, the royal tern is generally found in inshore waters, bays, lagoons, harbours, estuaries, saltmarshes and mangroves (3) (7) (8) (10) (13). It breeds on barren sandy beaches, as well as on offshore coral islands and man-made islands (3) (7) (9). The royal tern may rest on sandbars, mudflats and beaches, and is occasionally observed at inland lakes (7) (13).

An opportunistic feeder, the royal tern feeds predominantly on small fish, as well as squid and crustaceans (2) (8) (9) (12). It may also follow fishing boats, feeding on discarded bycatch (3). Generally, the royal tern forages alone or in pairs, but may aggregate in large flocks where prey is abundant (2) (3) (12), and especially when schools of predatory fish chase smaller fish towards the surface (12). It typically remains close to the shore during foraging trips, but may fly considerably further from the colony when searching for food to feed the young (3). The royal tern searches for its prey by flying low over the surface of the water and, once it has located suitable prey, it will plunge-dive vertically downwards, seizing the prey with its bill and swallowing it whole (2) (3).

North American and African populations of the royal tern typically breed between April and August (9) (11), and the South American population between October and March (11). It nests in large, dense colonies of several thousand pairs (8) (12), often in association with other species such as the laughing gull (Larus atricilla), the Caspian tern (Sterna caspia) and the sandwich tern (Sterna sandvicensis) (3) (9) (11).

Pairs perform courtship displays close to potential nest sites, often consisting of complex aerial displays, with much soaring and manoeuvring (3) (12) (13). The male royal tern will also approach the female on the ground, circling, strutting and raising its crest before offering food (14). Once pair bonds have been established, both the male and the female will select a nest site, circling the chosen area several times (2) (3) (14). 

The nest is a simple, shallow scrape in the ground. Both members of the pair contribute to building the nest, taking it in turns to scrape away the ground with the feet, before sitting and swivelling the body to round out the nest (2). The nest is typically positioned fairly close to the high tide line, on areas of open, bare ground with little or no vegetation (2) (9) (14). The royal tern defecates directly onto the rim of the nest to harden the edges, to give it some protection against flooding (2) (8). 

Colonies of royal terns have very high densities of nests, which become very tightly packed during the breeding season. The nesting pair defends a small territory directly around the nest, which extends to the reach of the incubating adult (12). The royal tern is fiercely defensive of its nest and young (5). A single egg is laid each breeding season, and both the male and the female royal tern share the incubation duties for 30 to 31 days (2) (3) (12).

Shortly after hatching, the royal tern chick leaves the nest and gathers together with other chicks, forming large crèches (2) (3) (8) (12) (13). This may also contain chicks of other species, such as the sandwich tern (2). The adult royal terns recognise their young by its call, and feed only their own chick in the crèche. The chick remains in the crèche until it fledges at 28 to 35 days old, during which time it is fed and brooded by both adults (2) (8) (13). Royal tern chicks have an extremely long period of post-fledging parental care (15), remaining dependent on the adult terns for feeding and protection for five to eight months after hatching (2) (3) (12). 

The royal tern is not currently considered to be at risk of extinction. However, the preferred breeding sites of this species are often vulnerable to flooding, and it is potentially threatened by the contamination of its prey with pesticides (9). The development of coastal areas may reduce nesting habitat in some parts of its range, forcing the royal tern to use alternative, less suitable nest sites (2). 

Overfishing may pose an additional threat to the royal tern by reducing populations of its main prey (9) (11). Egg collection is also known to occur at some breeding colonies of this species (2) (9). As a ground nesting species, the royal tern may also be vulnerable to predators, and to human disturbance at nest sites. In addition, oil spills and the discharge of sewage and chemicals into the sea are known to be negatively impacting seabirds, such as the royal tern, especially around the Rio de la Plata in Argentina and Uruguay (2) (11). 

The royal tern is included on the U.S. Migratory Bird Treaty Act and the Florida state Wildlife Code, which prohibits taking birds, nests, or eggs of this species. In Florida, most seabird colonies are designated as Critical Wildlife Areas and are posted and monitored by Florida Fish and Wildlife Conservation Commission and Audubon of Florida (7). Similar measures have been taken in North Carolina (2). There are no other known conservation measures currently targeted at this species (1).

Find out more about the royal tern and other bird species:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
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  1. IUCN Red List (March, 2011)
    http://www.iucnredlist.org/
  2. Buckley, P.A. and Buckley, F.G. (2002) Royal tern (Thalasseus maximus). In: Poole, A. (Ed.) The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
    http://bna.birds.cornell.edu/bna/species/700
  3. Avibirds European Birdguide Online - Royal tern (March, 2011)
    http://www.avibirds.com/euhtml/Royal_Tern.html
  4. Bridge, E.S., Jones, A.W. and Baker, A.J. (2005) A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution. Molecular Phylogenetics and Evolution, 35: 459-469.
  5. MobileReference. (2008) The Illustrated Encyclopedia Of European Birds: An Essential Guide to Birds of Europe. MobileReference, Boston.
  6. Blake, E.R. (1977) Manual of Neotropical Birds: Spheniscidae (Penguins) to Laridae (Gulls and Allies). University of Chicago Press, Chicago.
  7. Florida Natural Areas Inventory. (2001) Field Guide to the Rare Animals of Florida: Royal tern (Sterna maxima). Florida Natural Areas Inventory, Florida. Available at:
    http://www.fnai.org/FieldGuide/pdf/Sterna_maxima.pdf
  8. New Hampshire Public Television - Royal tern (March, 2011)
    http://www.nhchannel.org/wild/royaltern.asp
  9. BirdLife International - Royal tern (March, 2011)
    http://www.birdlife.org/datazone/speciesfactsheet.php?id=3260
  10. Raffaele, H.A. (2003) Birds of the West Indies. Princeton University Press, Princeton, New Jersey.
  11. Escalante, R. (1985) Taxonomy and Conservation of Austral-Breeding Royal Terns. Ornithological Monographs, 36: 935-942.
  12. Nellis, D.W. (2001) Common Coastal Birds of Florida & the Caribbean. Pineapple Press, Inc., Sarasota, Florida.
  13. Florida Fish and Wildlife Conservation Commission. (2003) Florida's Breeding Bird Atlas: A Collaborative Study of Florida's Birdlife. Florida Fish and Wildlife Conservation Commission, Florida. Available at:
    http://legacy.myfwc.com/bba/docs/bba_rote.pdf
  14. Quintana, F. and Yorio, P. (1997) Breeding biology of royal and cayenne terns at a mixed-species colony in Patagonia. The Wilson Bulletin, 109(4): 650-662.
  15. Perrins, C. (2003) The Encyclopedia of Birds. Oxford University Press, Oxford.