Least Tern

Least Tern
On the Atlantic coast, New Jersey, USA
Conservation status
Least Concern (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Charadriiformes
Family:	Sternidae
Genus:	Sternula
Species:	S. antillarum
Binomial name
Sternula antillarum (Lesson, 1847)
Synonyms
Sterna antillarum

The Least Tern (Sternula antillarum, formerly Sterna antillarum) is a species of tern that breeds in North America and locally in northern South America. It is closely related to, and was formerly often considered conspecific with, the Little Tern of the Old World. Other close relatives include the Yellow-billed Tern and Peruvian Tern, both from South America.

It is a small tern, 22–24 cm long, with a wingspan of 50 cm, and weighing 39–52 g. The upper parts are a fairly uniform pale gray, and the underparts white. The head is white, with a black cap and line through the eye to the base of the bill, and a small white forehead patch above the bill; in winter, the white forehead is more extensive, with a smaller and less sharply defined black cap. The bill is yellow with a small black tip in summer, all blackish in winter. The legs are yellowish. The wings are mostly pale gray, but with conspicuous black markings on their outermost primaries. In behavior, it flies over water with fast, jerky wingbeats and a distinctive hunchback appearance, with the bill pointing slightly downward.

It is migratory, wintering in Central America, the Caribbean and northern South America. Many spend their whole first year in their wintering area. It has occurred as a vagrant to Europe, with one record in Great Britain.

It differs from the Little Tern mainly in that its rump and tail are gray, not white, and it has a different, more squeaking call; from the Yellow-billed Tern in being paler gray above and having a black tip to the bill; and from Peruvian Tern in being paler gray above and white (not pale gray) below and having a shorter black tip to the bill.

Subspecies

Parent feeding a small chick in Florida, USA

• Sternula antillarum antillarum (Lesson, 1847). Breeds on the Atlantic coast of North America, from Maine south along the east and south coasts of the United States, Bermuda, the Caribbean, and Venezuela; winters south to northern Brazil.
• Sternula antillarum athalassos (Burleigh & Lowery, 1942). Breeds on the rivers of the Mississippi River, Brazos River, Trinity River, and Rio Grande basins; In the San Francisco Bay region, breeding typically takes place on abandoned salt flats. Where the surface is hard, this species may use an artificial indentation (such as a deep dried footprint) to form the nest basin.

The nest density may be as low as several per acre, but in San Diego County, densities of 200 nests per acre have been observed. Most commonly the clutch size is two or three, but it is not rare to consist of either one or four eggs. Both female and male incubate the eggs for a period of about three weeks, and both parents tend the semiprecocial young. Young birds can fly at age four weeks. After formation of the new families, groupings of birds may appear at lacustrine settings in proximity to the coast. Late-season nesting may be renests or the result of late arrivals. In any case, the bulk of the population has left the breeding grounds by the end of August.

Feeding and roosting characteristics

Least Tern (Sternula a. antillarum) at Lake Jackson, Florida

The Least Tern hunts primarily in shallow estuaries and lagoons, where smaller fishes are abundant. It hovers until spotting prey, and then plunges into the water without full submersion to extract meal. In the bays and lagoons of Southern California and northern Mexico, the favored prey include anchovy, smelt, silversides, shiner perch, and small crustaceans. Sometimes the terns feed near shore in the open ocean, especially in proximity to lagoons or bay mouths.

Adults do not require cover, so that they commonly roost on the open ground. After young chicks are three days old, they are brooded less frequently by parents and require wind blocks and shade. Notable disruption of colonies can occur from predation by Burrowing Owls and American Kestrels. Predation by domestic cats has been observed in at least one colony. Predation on inland breeding terns by Coyotes, Bobcats, feral dogs and cats, Great Blue Herons, Mississippi Kites, and owls has also been documented (Jones 1997-2006).

References

• National Geographic Society (2002): Field Guide to the Birds of North America. National Geographic, Washington DC. ISBN 0-7922-6877-6
• Audubon Handbook: Western Birds (1988) McGraw Hill Book Company, ISBN 0-07-019977-9
• Massey, B. (1974) Breeding Biology of the California least tern, Proceedings Linn. Society, New York 72:1-24
• Gary Deghi, C. Michael Hogan, et al., Biological Assessment for the Proposed Tijuana/San Diego Joint Innternational Wastewater Treatment Plant, Publication of the U.S. Environmental Protection Agency Region IX, Earth Metrics Incorporated, Burlingame, CA with Harvey and Stanley, Alviso, CA
• Olsen and Larsson, Terns of Europe and North America ISBN 0-7136-4056-1

External links

• Photo Field Guide on Flickr
• Least Tern Bird Sound