Sterna sandwicensis

Sandwich Terns, named for the village of Sandwich in Kent, England where the type specimen was taken, are sometimes placed in a separate genus with other “crested terns.” Morphological and genetic studies suggest the closest relatives of Sandwich Terns are Elegant (S. elegans) and Lesser Crested (S. bengalensis) terns. Hybrids between these two species and Sandwich Terns have been reported (Shealer 1999).

Sandwich Terms are divided into 2 groups, often considered separate species. The Cayenne Terns (S. s. eurygnatha) of South America have straw-yellow to orange-yellow bills and larger crests than North American and Eurasian birds (S. s. sandwicensis). The taxonomy is complicated by range overlap in the Caribbean in breeding season and some hybridization in the southern Caribbean (Am. Ornithol. Union 1998, Shealer 1999).

DISTRIBUTION. During the 1987-1992 field work seasons of the TBBA project, observers found 79 confirmed, 5 probable and 12 possible breeding sites along the Texas coast in the Coastal Prairies, Coastal Sand Plain and South Texas Brush Country regions (see the region map in Lockwood and Freeman [2004]).

In North and Middle America, Sandwich Terns breed locally on the Atlantic Ocean from Virginia to Florida, the Gulf Coast from Florida to Texas, both coasts of Mexico, off  Belize and in the West Indies. Other populations breed locally along the Atlantic Coast of South America, the Atlantic and Mediterranean costs of Europe and around the Black and Caspian seas. Northern North American populations winter further south in the breeding range and along the coasts of northern South America (Howell and Webb 1995, Am. Ornithol. Union 1998, Shealer 1999).

SEASONAL OCCURRENCE. Sandwich Terns are present all year along the Texas coast, although in winter they are rare to uncommon. Breeding occurs from mid-April to mid-July as indicated by egg collection dates from April 25 to July 2. Tropical storms sometimes blow Sandwich Terns inland to locations like Austin and Falcon Reservoir (Oberholser 1974, Lockwood and Freeman 2004).

BREEDING HABITAT. Sandwich Terns breed in Texas near sea level (Oberholser 1974). In North America  they usually nest colonially on flat, sandy islands close to shore. The pairs alternate digging a shallow depression while sitting on the sand. The diameter of the scrape varies with the firmness of the substrate; one study found 7-10 cm (3-4 in). Here the female customarily lays one or two smooth, white to pale buff eggs with a wide variety of dark markings. Both male and female Sandwich Terns develop brood patches and share incubation duties before the eggs hatch, about 23-25 days. The semi-precocial chicks open their eyes within a few hours and leave the nest within 1-2 days. Chicks usually join groups of their peers within 3 weeks  after nest leaving. The parents feed them whole fish. Chicks fledge at 27-29 days after hatching, when they take their first flights. A few days later the parents and young leave the nesting colony and the fledglings begin learning to forage using plunge-dives. One or both adults continue to feed juveniles at least until fall migration. These terns probably begin breeding in North America  4 to 5 years after hatching, based on data from England, then breed annually (Shealer 1999).

STATUS.Sandwich Terns are common summer residents along the Texas coast (Lockwood and Freeman 2004). The coastal distribution of breeding and summer symbols on Oberholser’s (1974) map is quite similar to that on the TBBA map. In Louisiana  the Chandeleur Islands have the largest Sandwich Tern colonies in the world with over 20,000 nests annually (Shealer 1999). Loss of the Louisiana and Texas colonies could be devastating for this species in the United States.

Literature cited.

American Ornithologists’ Union. 1998. Checklist of North American birds, 7^th ed. Am, Ornithol. Union, Washington, DC.

Howell, S. N. G. and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford University Press, New York.

Lockwood, M. W. and B. Freeman. 2004. The TOS handbook of Texas birds. Texas A&M University Press, College Station.

Oberholser, H. C. 1974. The bird life of Texas. University of Texas Press, Austin.

Shealer, D. 1999. Sandwich Tern (Sterna sandwicensis), The Birds of North America Online (A. Poole, Ed.). Cornell Lab of Ornithology; Ithaca, NY: Retrieved from: http://bna.birds.cornell.edu/bna/species/405