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 Elegant 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.
This medium-sized tern with a long, shaggy crest, a pink flush on its belly feathers, and a distinctive bill, has the most restricted breeding distribution of any tern in North America (see Figure 1). It nests in isolated mainland or insular colonies, among larger, more aggressive larids—primarily Heermann's Gulls (Larus heermanni) and Caspian Terns (Sterna caspia). Historically, at least a dozen breeding colonies existed, but commercial egging and the introduction of mammalian predators appear to have eliminated most of them. Only 5 nesting colonies remain, and 90–97% of the world's Elegant Tern population breeds on Isla Rasa, Mexico. Such limited distribution makes the species highly vulnerable and a “Species of Special Concern” in California.
After breeding, Elegant Terns disperse north and south along the coast from their nesting colonies. In southern California, breeding success and dispersal patterns appear related to oceanographic conditions, particularly El Niño–Southern Oscillation events, which affect the distribution of key prey, the northern anchovy (Engraulis mordax). A strongly social bird, this tern nests in tight groups and, when feeding in a flock, calls frequently. Individuals generally lay a single egg but have 2 brood patches. After hatching, the chick remains in the nest scrape only a few days; then, like young of other crested terns, it joins creches—large groups of chicks in which each individual is fed by its own parents. Because foraging skills are difficult to learn in this species, postfledging parental care lasts at least 5–6 months.
Compared to most other terns, the Elegant Tern has been little studied, and most work has been concentrated at 2 California colonies. Schaffner's ( Schaffner 1982 ) research was especially comprehensive and covered reproductive biology, individual recognition, diet, and general natural history. Kirven ( Kirven 1969 ) reported general breeding biology, while Evans ( Evans 1973a ) focused on breeding behavior. Extensive data on prey selection and diet are reported in Tordesillas 1992 , Loeffler 1996 , and Horn et al. 1996b .