The Royal Tern (Thalasseus maximus) is a large white tern with an orange-yellow bill and a black crest. It is common along many tropical and subtropical shores of the Americas and West Africa. (Kaufman 1996; AOU 1998)
Conservation and Management
The Royal Tern is not globally threatened, although populations are declining in several areas. In the southeastern United States, numbers increased in the early 1900s (following a decline resulting from egg gathering for food) and the species slowly extended its range northward, breeding as far north as Maryland and, rarely, New Jersey. The East Coast population is about 34,000 pairs, the Caribbean population fewer than 1000 pairs, and the French Guiana (Cayenne) population is about 100 pairs, but the numbers of this tern in most of South America are not known. In California, the population crashed with the radical decline of the Pacific Sardine in the last decades of the 20th century. Around 25,000 pairs are believed to breed in Africa. (Gochfeld and Berger 1996; Kaufman 1996). Although the population numbers for most of South America are not well known, Yorio and Efe (2008) estimated the total Royal Tern population size as at least 750 pairs in Brazil and fewer than 5000 in Argentina.
Yorio and Efe (2008) listed the threats to Royal Tern populations in Brazil and Argentina as human disturbance, fisheries, egging, and expanding Kelp Gull (Larus dominicanus) populations.
The Royal Tern usually feeds singly or in small flocks, despite its tendency to roost in larger numbers. It typically flies 5 to 10 meters above the water and plunge-dives (but does not submerge). It also performs aerial skimming and surface-dipping for bits of food that may be floating on the surface. It occasionally steals food from other individuals. Most foraging occurs within 100 meters of shore, but it may feed up to 40 km from the colony. (Gochfeld and Berger 1996) It may sometimes feed at night (Kaufman 1996).
The Royal Tern is found on seacoasts, around lagoons and estuaries, and at sea over the continental shelf (AOU 1998).
The Royal Tern is found along tropical and subtropical coasts. It breeds on barren sandy barrier beaches, salt marsh islands, shell bars, dredge spoil, and coral islands. It shuns vegetation. Many colony sites are vulnerable to flooding. Breeding colonies typically are difficult to access (except by flight), offer high visibility, lack mammalian predators, and are surrounded by shallow water near the mouths of bays. It feeds around estuaries, lagoons, and mangroves. Outside the breeding season, it is found along coasts and and around estuaries, harbors, and the mouths of rivers, sometimes traveling a short distance up broad rivers. (Gochfeld and Berger 1996)
In North America, the Royal Tern is found along coasts, around sandy beaches, and in bays, lagoons, and estuaries. It may also be found well offshore and in the Caribbean frequently travels between islands. At least in North America, it is rarely found inland, except for a few interior localities in Florida. It typically nests on low-lying sandy islands. (Kaufman 1996)
In Africa, the Royal Tern breeds from Mauritania to Guinea, occasionally farther south, and winters south to Namibia. In the New World, it is found from southern California to Sinaloa and from Maryland (rarely New Jersey) to Texas and through the West Indies to the Guianas and possibly Brazil, with disjunct breeding populations in Yucatan and in southern Brazil, Uruguay, and northern Patagonia; it winters south to Peru and to Uruguay and Argentina. (Gochfeld and Berger 1996)
The Royal Tern breeds locally on the Pacific Coast of North America, in southern California, along the coast of Sinaloa and Sonora; in the Atlantic-Gulf-Caribbean region it breeds from New Jersey and the Gulf coast south through the West Indies to islands off the north coast of Venezuela and French Guiana, and in Yucatan; in South America, it breeds on the coast of northern Argentina; and in West Africa, it breeds on islands off Mauritania. Nonbreeders occur in summer in coastal areas in the Americas north to central California and Maine, and south through the wintering range (rarely on the Pacific coast south of Mexico). Wintering range is from central California, the Gulf coast, and North Carolina south along both coasts of the Americas to Peru, Uruguay, and Argentina; and on the west coast of Africa from Morocco to Angola (casually to southern Africa). (AOU 1998)
In the New World, the Royal Tern winters from South Carolina and the Gulf Coast to Argentina, very rarely along the Peruvian coast. Chicks banded in South Carolina colonies were recovered mainly along the Gulf Coast, Florida, and the West Indies. Chicks banded in Virginia were recovered mainly in the Greater Antilles. West African birds disperse north to Morocco; most then move south to winter from Senegal to Angola, with smaller numbers south going to Namibia. (Gochfeld and Berger 1996)
In most of its breeding range, the Royal Tern is present year-round. On the Atlantic coast of North America, some birds wander north of the breeding range in late summer. In California, the Royal Tern is more common in winter than in summer. (Kaufman 1996)
The longest recorded lifespan for a Royal Tern is 17 years, but according to Gochfeld and Berger (1996) this is surely an underestimate.
The Royal Tern lays eggs in April to July in West Africa, in April in Texas, in May from Florida to Maryland, in June in Cayenne, and in November in Patagonia. Breeding colonies are dense and often quite large, frequently near Laughing Gulls (Larus atricapillus) or Sandwich Terns (Thalasseus sandvicensis). Most colonies contain 100 to 4000 breeding pairs. Density is about 5 to 8 nests per square meter. The Royal Tern occasionally nests singly in colonies of other tern species (usually at the edge of its geographic range). The nest consists of a simple scrape in the substrate (in Florida, it sometimes nests on rooftops). Clutch size is generally one (although adults have 2 brood patches), but 1 to 10% of birds may lay a second egg. Incubation period is 25 to 35 days. Young fledge at about 30 days post-hatching, but receive care from parents for 5 to 8 months and migrate south with them. First breeding is at 3 to 4 years of age. (Kaufman 1996; Gochfeld and Berger 1996)
The Royal Tern feeds mainly on small fish (3 to 18 cm, average 6 to 7 cm) as well as squid, shrimp, and crabs. In Africa, reported prey are mostly in the fish families Clupeidae, Mugilidae, Pomadasyidae, Carangidae, and Ephippidae. In Virginia, reported prey include Menidia, Fundulus, Anchoviella, and Brevoortia. In Florida, prey include Brevoortia and Micropogonias. In California, the Royal Tern relies heavily on Pacific Sardine (Sardinops sagax). (Gochfeld and Berger 1996) On the Atlantic coast of the United States, soft-shelled (newly molted) Blue Crabs are a major component of the diet (Kaufman 1996).
In a study of Royal Tern chick diet in Virginia, terns foraged largely on anchovy (Anchoa spp.) early in the season, then switched to herrings (family Clupeidae); average prey size also increased seasonally (Aygen and Emslie 2006). In a North Carolina study, systematic observations of adults returning with food indicated that at least 18 families of fish, squid, and crustaceans were exploited, the most common forage species in both years being anchovies (Engraulidae), herring (Clupeidae), and drum (Sciaenidae) (Wambach and Emslie 2003).
The Sandwich Tern (Thalasseus sandvicensis) and Royal Tern overlap in their distribution and often nest in the same colonies. McGinnis and Emslie (2001) studied the foraging ecology of these two terns in South Carolina and found that the two species partition food resources by spending significantly different proportions of their foraging time in different habitats and feeding on a significantly different set of prey.
Where the two species occur together, Kelp Gulls (Larus dominicanus) may steal food from Royal Terns bringing it back to feed their chicks (Quintana and Yorio 1999).
Eggs may be destroyed by sand crabs (Ocypoda arenaria). Black-headed Gulls (Chroicocephalus ridibundus) take both eggs and chicks, but Laughing Gulls (Leucophaeus atricilla) take only eggs. (Gochfeld and Berger 1996) At least occasionally, egg predation by Ruddy Turnstones (Arenaria interpres) may be quite severe (Loftin and Sutton 1979).
Dronen et al. (2007) described a new digenean trematode flatworm parasite from Royal Tern and provided a list of all parasites previously reported from this species.
Evolution and Systematics
Systematics and Taxonomy
Bridge et al. (2005) analyzed the mitochondrial DNA of a large fraction of the world's terns and correlated the results with plumage characters. Based on their new data on phylogenetic relationships among tern species, they suggested resurrecting several old genus names--including Thalasseus for the Royal Tern and several close relatives--to make nomenclature better match current understanding of relationships. This recommendation was endorsed by the American Ornithologists' Union Committee on Classification and Nomenclature (Banks et al. 2006), so the name Thalasseus maximus (Boddaert) for the Royal Tern is likely to be rapidly and widely accepted.
Mayr and Short (1970) considered the Royal Tern (T. maximus) and the Great Crested Tern (T. bergii) to together constitute a superspecies.