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LEAST TERN (Sterna antillarum)

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Least tern picture 1
Family: Laridae

Order: Charadriiformes

STATUS: Threatened

DESCRIPTION: The small size (23 centimeters long) of the least tern immediately distinguishes this summer resident from other terns. It arrives in early spring (March-April) in Florida in breeding plumage: forehead pure white, cap black, bill yellow with a black tip, legs and feet yellow to orange. Underparts and tail are white, back and wings pale gray, the two outer primaries dark gray to black. The tail is only moderately forked. Juveniles are pale gray with brown or buff mottled backs, black bills, and blackish outer primaries and greater and lesser coverts. Sexes are alike at all ages. The flight is light, buoyant, and erratic, with a rapid wingbeat and with the head pointing down scanning the water surface for food, in typical tern fashion.

HABITAT AND DISTRIBUTION: The natural habitat is open, flat beach with coarse sand or shell, usually seaward or within the foredune vegetation. But the species is opportunistic and will use any gravely or sandy area that is devoid of vegetation and which provides suitable habitat, such as spoil created by man's dredge-and-fill operations, parking lots, on bridge or building construction sites and temporary landfills. While primarily a coastal bird, colonies have been reported from the interior, most recently from Orange, Okeechobee, and Highlands counties. The species has a worldwide distribution.

Least tern picture 2In the eastern United States, the species S. antillarum breeds from Louisiana to the Dry Tortugas and Key West and northward on the Atlantic Coast to southern Maine.

LIFE HISTORY AND ECOLOGY: In Florida least tern colonies begin nesting in April and continue through September. If disturbed, they move and renest, evidently repeatedly. In recent years least terns have been observed nesting on flat roofs where tar and gravel compositions bear some resemblance to beaches. The rooftops may be located several miles from feeding grounds. Nests are shallow scrapes in sand or shell at least 1.2 meters apart. Several scrapes sometimes are made before one is settled on. Eggs are whitish, with variable dark spots and blotches, well camouflaged which undoubtedly provides protection from predators. Clutch size is two, sometimes three, rarely one, with both sexes incubating. The time of incubation varies from 20 or 21 days. If disturbed the hatchlings remain in, or close to, the nest for 2 or 3 days, and are brooded possibly for a longer period. At 4 weeks or more the birds can fly strongly. The tern's diet consists of mainly small fish and, to a much lesser extent, crustaceans and insects that they obtain from shallow waters. When disturbed least terns are aggressive, rising with shrill, high-pitched cries to attack animals, man, and even the largest birds. Known predators include snakes, crows, raptors, rats, raccoons, cats, dogs, and man.

BASIS OF STATUS CLASSIFICATION: By 1900 the species had been nearly extirpated by egg collectors and plume hunters. It suffered greatly in those days, and long after the killing stopped it seemed unable to recover its former numbers. In a recent study of the Florida and Atlantic Coast colonies it has been calculated that less than 20 percent of least tern nesting is now on the natural areas of beaches and dunes. The balance is on man-made habitat, much of which is dredged spoil which can be utilized by nesting least terns only so long as it does not become covered by vegetation, or is not so steep that it erodes away, or is not actively used by man. As a result of land development and a burgeoning population, least terns have deserted or lost many of their traditional breeding grounds. In response to these losses and continued threats to their population, the least tern has been listed as "threatened" by the state in 1975. Additional protection is afforded by the federal Migratory Bird Treaty Act, which has been adopted by the state.

HABITAT GUIDELINES: Protection of this species consists of providing an effective zone that buffers the nesting sites. This "buffer zone" may extend into upland habitat. The extent of these buffers is based on existing State and/or Federal guidelines, or reflect the recommendations of the Florida Game and Fresh Water Fish Commission.

Any activity proposed within a buffer zone would be subject to review. Activities that could be allowed in the buffer zone would be those activities which would not have any long term detrimental impact on the nesting birds. The following would be considered when making this determination: (1) the type of activity or construction planned and its' long term impacts; (2) the nature of the natural community that makes up the buffer zone (does it provide a visual barrier for any proposed nesting activities?); and (3) the timing of the proposed construction (does it occur outside the nesting season?).

RECOMMENDATIONS: Despite the legal restrictions, land development and human population growth continue to usurp the species' habitat. Only through protection of existing breeding areas can the continued existence of the least tern be assured in Florida. Beaches where the birds are known to nest on federal, state, or city property should be posted and restricted during the nesting season.

REFERENCES:
O'Meara, T.E. and J.A. Gore. 1988. Guidelines for conservation and management of least tern colonies in Florida. Florida Game and Fresh Water Fish Commission. 12pp.

Content updated Date February 24, 2005