Multigene phylogeny and DNA barcoding indicate that the Sandwich tern complex ( Thalasseus sandvicensis, Laridae, Sternini) comprises two species

Abstract

The crested terns are a group of six species of seabirds with a world-wide distribution closely allied to but larger than typical Sterna species. They are black-capped with elongated crest feathers and most have a bright yellow or orange to orange–red bill (Gochfeld and Burger, 1996). The taxonomic status of this group as a separate genus, Thalasseus, is gaining increasing acceptance following the publication of a molecular phylogeny demonstrating they form a strongly supported monophyletic clade (Bridge et al., 2005). One of the remaining taxonomic uncertainties in the Sternini is in the classification of the species complex of the Sandwich tern (Thalasseus sandvicensis), a taxon whose definition and limits have been controversial over the last century. Within this complex, there are three forms that have been classified either as subspecies or species. The most frequent treatment is to consider them as three subspecies: the Sandwich tern (T. s. sandvicensis) that breeds on the Atlantic and Mediterranean coasts of Europe, Cabot’s tern (T. s. acuflavidus) that breeds on the Atlantic coasts of North America and the Caribbean, and Cayenne tern (T. s. eurygnathus) that breeds on the Atlantic coast of South America from Argentina north to the Caribbean. The three races of Sandwich tern were originally described as distinct species (Baird et al., 1884), and due to their morphological and behavioral similarities were later suggested to be part of the same species complex (Baird et al., 1884; Junge and Voous, 1955), an issue that is still controversial (Gochfeld and Burger, 1996; Hayes, 2004). These taxa are morphologically very similar, with a few distinctions: the Sandwich tern is slightly larger with wider white margin on outer primaries, shorter bill and, paler upperparts (Olsen and Larsson, 1995). Cabot’s and Cayenne terns are virtually identical