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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 Sandwich 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.
A common but local summer resident of the southeastern Atlantic and Gulf coasts, the Sandwich Tern is easily identified because it is the only “crested” tern with a black bill. It is also one of the most gregarious and colonial of all birds during the breeding season. Found almost exclusively along coastal areas and offshore islands, a nesting colony of Sandwich Terns conjures up a chaotic scene: Birds arriving and departing every second, neighbors no more than a bill length apart squabbling over territorial rights, fish changing ownership between males and females and between parents and their young, a pervasive odor of seabird guano in the air, and the deafening chatter that is characteristic of a few thousand birds crammed into a few square meters of nesting habitat.
Three subspecies of Sandwich Tern are recognized. Two resemble each other closely, Sterna s. sandvicensis in the Old World and S. s. acuflavida, also known as Cabot’s Tern, in the New World. A third subspecies, S. s. eurygnatha, also called Cayenne Tern and sometimes treated as a separate species, has a rather distinctive yellow bill rather than black bill with yellow tip typical of the other two races. The Cayenne Tern is found from the southern Caribbean southward along the Atlantic coast of South America. This account focuses on the northern subspecies, but includes information available on the southern subspecies.
In the United States, Sandwich Terns almost always nest in dense groups among Royal Terns (S. maxima), Laughing Gulls (Larus atricilla), and sometimes Black Skimmers (Rynchops niger). In Caribbean colonies, they are obligate nesters with Royal Terns and Roseate Terns (S. dougallii). The situation is similar in the Old World, with the only difference being the cast of characters. There Sandwich Terns are found in colonies with Black-headed Gulls (L. ridibundus), Common Terns (S. hirundo), and Arctic Terns (S. paradisaea). Reasons for such a close association with other species may relate to the need for similar nesting habitat or to the relatively nonaggressive nature of Sandwich Terns; by nesting with other more aggressive species, Sandwich Terns may benefit by “parasitizing” protection against predators.
Although populations in the United States and Caribbean appear to have been relatively stable, or even increasing, over the past several decades, exact estimates of numbers and trends are difficult to obtain because the species tends to shift nesting sites annually. Sandwich Terns have expanded their breeding range northward along the Atlantic coast over the past century and are now common breeders in North Carolina; recent nesting has also been confirmed in Virginia and Maryland.
For nearly half a century the Old World populations of Sandwich Tern have been the subject of intensive studies of behavior, feeding ecology, and population dynamics. Much less work has been done in North America. Over the past 20 years, only a few studies in the New World have been conducted on important topics such as basic reproductive biology (Blus et al. 1979, Quintana and Yorio 1997), population dynamics (Visser and Peterson 1994, Parnell et al. 1997), feeding behavior and ecology (Shealer 1996, 1998, Shealer and Burger 1995, Shealer et al. 1997), and pollutants (White et al. 1979, Maedgen et al. 1982). As a result, much of the information contained in this account pertains to the Old World populations and exemplifies the need for more detailed investigation in North America.