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 the Sandwich Tern are recognized. Two resemble each other closely, Thalasseus s. sandvicensis in the Old World and T. s. acuflavidus, also known as Cabot’s Tern, in the New World. A third subspecies, T. s. eurygnathus, 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 subspecies. 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 (Thalasseus maximus), Laughing Gulls (Leucophaeus atricilla), and sometimes Black Skimmers (Rynchops niger). In Caribbean colonies, they nest exclusively with Royal Terns and Roseate Terns (Sterna 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 (Chroicocephalus ridibundus), Common Terns (S. hirundo), and Arctic Terns (S. paradisaea). The 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; further, 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, accurate estimates of numbers and population 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, and recent nesting has been confirmed as far north as Virginia and Maryland.
For nearly half a century, Old World populations of Sandwich Tern have been the subject of intensive studies of behavior, feeding ecology, and population dynamics. However, over the past few decades an increasing number of studies in the New World have been conducted on basic reproductive biology (Blus et al. 1979c, Quintana and Yorio 1997, Fracasso et al. 2011, Raynor et al. 2012, Owen and Pierce 2014), population dynamics (Visser and Peterson 1994, Parnell et al. 1997, Jodice et al. 2007, Emslie et al. 2009, Raynor et al. 2013, Liechty 2014), feeding behavior and ecology (Shealer 1996, Shealer 1998, Shealer and Burger 1995, Shealer et al. 1997, Favero et al. 2000, McGinnis and Emslie 2001, Gatto and Yorio 2009, Wickliffe and Jodice 2010, Jodice et al. 2011, Liechty et al. 2016), interspecific interactions (Quintana and Yorio 1998, Quintana and Yorio 1999, Garcia et al. 2010), genetics (Efe et al. 2009, Velarde and Rojo 2012), pollutants (White et al. 1979a, Maedgen et al. 1982), and sex determination (Lisnizer et al. 2014).