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Royal Tern
Thalasseus maximus
Order
CHARADRIIFORMES
– Family
LARIDAE
Authors: Buckley, P. A., and Francine G. Buckley

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Introduction

Adult Royal Tern, non-breeding plumage; Florida, October
Adult Royal Tern, breeding plumage;
Figure 1. Distribution of the Royal Tern

Editor’s Note: Study of the mitochondrial DNA of terns, along with their plumage characteristics, have suggested that the heretofore broadly defined genus Sterna is paraphyletic. Reclassification of this genus now places Royal Tern in the genus Thalasseus. See the 47th Supplement to the AOU Check-list of North American Birds for details. Future revisions of this account will account for this change.

The loud, rolling “ Keer-reet ” call of foraging Royal Terns is among the most conspicuous and typical summer sounds of the mid-Atlantic and Gulf Coasts, as well as of Caribbean and southern California waters in fall and winter. A quintessentially saltwater species, this tern feeds inshore along barrier beach oceanfronts and back bays, occasionally ranging farther offshore when foraging, especially when feeding chicks.

For such a conspicuous bird, it is astonishing to discover that the normally discerning John J. Audubon himself confused it throughout his life with Caspian Tern (Sterna caspia). In his monumental Birds of America, Audubon depicted neither Caspian nor Royal, but instead what he called a Cayenne Tern, Sterna cayana — mostly Royal, but with some ad-mixture of Caspian features.

In the Western Hemisphere, Royal Tern is the flagship species among the crested terns, a cosmopolitan but essentially pantropical group characterized by conspicuous crests, extremely dense breeding colonies, continuously variable downy chicks and juveniles, the formation of crèches (common nurseries for prefledging chicks), extended parental care, and delayed first breeding. The crested terns have in the past been placed in their own genus, Thalasseus, a practice today abandoned by nearly all authors.

Royal Tern breeding populations occur in 4 or 5 separate geographic regions: Atlantic and Gulf coasts of North America and Caribbean, Yucatán Peninsula, Pacific coast of Mexico (north to southern California), southeastern South America, and central-west coast of Africa. These currently are divided into 2 subspecies, with all New World populations ascribed to nominate Sterna maxima maxima and Old World populations ascribed to S. m. albididorsalis . Breeding colonies favor traditional sites at isolated locations, free of terrestrial predators; in the United States, dredge-spoil islands have become key to the survival and expansion of the species.

In winter, Royal Terns retreat south from the extreme northern edges of their postbreeding range; increasingly common southward from the Outer Banks of North Carolina, they are among the most typical species in the West Indies. Individuals often move great distances in winter, routinely reaching Suriname and Peru. Typically noisy and highly social, they are conspicuous wherever they occur.

The most extensive studies of boreal populations of S. m. maxima have been those of the authors of this account (Buckley and Buckley 1969, 1970, 1972a, 1972b, 1974, 1976, 1977; Buckley and Hailman 1970; and Buckley et al. 1985) and, currently, Steven Emslie and colleagues (Maness 2000; McGinnis 2000; Wambach 2000; Maness and Emslie 2001; McGinnis and Emslie 2001). Austral S. m. maxima was first discussed by Rodolfo Escalante (1968, 1985), and aspects of its biology have recently been examined by Flavio Quintana and Pablo Yorio (Quintana and Yorio 1997, 1998, 1999; Yorio and Quintana 1997). In general, however, most populations of all the crested terns remain conspicuously unstudied, a pity considering their fascinating social systems.