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Gregory R. Mann, Ph.D. {ret.}

Royal Tern

“Thalasseus maximus”

The Royal Tern is the second-largest tern. In gatherings of gulls and terns, it is usually quite easily identified by its larger size, its distinctive black crest and bright orange bill. Adult in breeding plumage has black crown and elongated feathers on the nape. On the upper-parts, mantle and upper-wing are very pale grey. Rump and tail are white. The stout bill is bright orange. Eyes are dark brown. Legs and feet are black. This common seabird is found along many tropical and subtropical shores of the Americas and West Africa. A group of Royal Terns is collectively known as “highness”. The oldest recorded Royal Tern was 30+ years. Adult in non-breeding plumage has white forehead. The crown is white with black streaks. The black color of the nape extends forwards to the eye. On the wings, the outer primaries are faintly dusky above. The tail is slightly forked. Both sexes are similar. Juvenile resembles adult in basic plumage, but the upper-parts shows dark spots and marks. Tail is pale gray with dark tips. Their first summer is much like adult in basic plumage, with dark bar on secondary feathers. Outer primaries and tail are dark-tipped. Their second summer shows white flecks in the black cap. They reach their sexual maturity at 3-4 years. Royal Terns frequent subtropical and tropical coasts. This species breeds on sandy barrier beaches, salt-marsh islands and coral islands. Many sites are vulnerable to flooding, but the colonies are characterized by inaccessibility, good visibility, and absence of mammal predators. The sites are surrounded by shallow water near the bays. Royal Terns may be found along estuaries and mangroves where it feeds. After the breeding season, this species frequents coasts, estuaries, harbors and river mouths.

Royal Terns breed on the Atlantic and Pacific coasts of southern North America and Mexico, West African coasts and into the Caribbean. They winter in Peru, Argentina and on the Namibian coasts. It feeds alone or in small groups, by flying some meters above the surface and dives, but does not submerge. It also may perform aerial skimming and take offal by surface-dipping. As other seabirds, the Royal Tern sometimes engages in piracy from other terns. This species usually forages within 100 meters from the coast, but often up to 30-40 kilometers from the colony. The Royal Tern is gregarious, breeding in colonies and roosting in flocks. Colonies may contain hundreds and sometimes thousands of pairs. In such huge density, we can find up to 8 nests by square meter. It is also a good protection against aerial predators which are not able to land within the colony. The Royal Tern is territorial and defends its small space by walking or flying towards opponents, by aerial chases, flutter flights and several kinds of displays with head movements. Courtship displays can occur both on the ground and in the air. Usually, the male brings back a fish for the female. She may swallow it immediately but sometimes, she keeps it in the bill during the displays. Displays include “high-flight” or “fish-flight”. Both birds take off and fly high in the air in tandem, with alternated glides. When the pair is formed, the displays accelerate and we can observe frequent courtship feeding. Female defends the territory while the male feeds her regularly. Later, copulation follows the fish-transfer. Breeding season varies according to the range. The Royal Tern breeds in huge colonies near other gull’s species. Colonies are very dense with 5 to 8 nests per square meter. The nest is a scrape in the soil. Female lays one egg. Incubation lasts about 25 to 31 days, shared by both adults. Both have brood patches. At hatching, the chick is grayish or buffy with dark spots. Chicks may form crèches. The young fledges about 1 month after hatching, but it still depends on parents for 5 to 8 months. The Royal Tern feeds on small fish (in average 6-7 centimeters long), squid, shrimps and crabs.

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