The least tern is the smallest of the North American terns. During the breeding season least terns exhibit gray plumage above with black on the head and nape of the neck. The birds' foreheads are white, their tails are forked, and their bills are yellow/orange with black tips. Juveniles are dusky with brown markings on the back, and they develop the adult plumage at 1-2 years of age. Female and male least terns are not sexually dimorphic; they exhibit the same coloration. Least terns measure 23 cm (9 in) long with a 50 cm (20 in) wing span.
Habitat and Biology
The least tern's breeding range includes coastal areas in California and along the eastern seaboard from Maine to Florida, as well as the Mississippi River area. Thus, they are summer residents in coastal South Carolina, and nesting terns are found at 12 locations on the coastal islands of the ACE basin. Winters are spent on the Pacific coast of Mexico and South America.
Least terns begin breeding at 2 years of age. They are monogamous (one breeding partner at a time) and produce one brood per year. In South Carolina, nesting occurs around mid-May. Terns nest in colonies on beaches and sandbars with abundant shells and pebbles and sparse vegetation. Females construct unlined nests on the ground, and both adults incubate 1-3 eggs for approximately 20 days. Least terns have the habit of shaking water on their eggs, which cools them as it evaporates. In an effort to protect their nests from predators, least terns actively harass and defecate over intruders. After hatching, young terns fledge in about 20 days. Constant hovering over water allows least terns to locate the aquatic invertebrates and small fish on which they feed.
The least tern is currently threatened in South Carolina. Among the most important factors that have contributed to the species' decline are over-hunting for the millinery industry (plumage hunters) in the early twentieth century and abandonment of nesting sites due to human disruption. Mammalian predators such as rodents, raccoons, and cats have also taken their toll. In addition, least terns tend to construct their nests in low-lying sandbars that are sometimes flooded by very high tides.
Bull, J. L. and J. Farrand, Jr. 1995. National Audubon Society Field Guide to North American Birds. Eastern Region. The Audubon Society field guide series. Alfred A. Knopf Inc., New York, NY.
Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988. The birder's handbook: A field guide to the natural history of North American birds, including all species that regularly breed north of Mexico. Simon & Schuster, New York, NY.
National Geographic Society. 1987. Field guide to the birds of North America. Second edition. National Geographic Society, Washington, DC.
Sprunt, A., Jr. and E. B. Chamberlain. 1970. South Carolina bird life. University of South Carolina Press, Columbia, SC.