Least Tern

IDENTIFICATION: The Least Tern is the smallest tern nesting in Puerto Rico. It is white with light gray upperparts, a black cap, orange or yellow legs, and a bright yellow bill with a black tip. Immature Least Terns have a black bill and a distinct black ear patch, but their yellow legs, black wing bar in flight, and small size distinguish them from other tern species. Length: 21-23 cm.; weight: 47-50 g.

VOICE: When disturbed at nesting colonies, it makes a grinding call, "zwreep." Audio (M. Oberle).

HABITAT: Shallow coastal marine waters and inland lagoons.

HABITS: The Least Tern hovers about 1-10 meters above the ocean surface before plunging into the water for small fish, 2-9 cm. long. It will also eat shrimp and other marine invertebrates. It nests in small colonies on bare sandy beaches and the edges of salt ponds and lagoons, where each monogamous pair builds a nest scrape, adorned with bits of shells and pebbles. The female lays 2-3 eggs and does most of the incubating. In extremely hot temperatures, the adults will soak their feathers in water, and then drip the water onto the eggs or chicks to cool them. After 20-22 days of incubation, the chicks hatch and then walk away from the nest after a few days. Both parents feed the chicks even after they fledge, 20 days after hatching. The Least Tern often does not breed until three years of age.

STATUS AND CONSERVATION: Breeds in small numbers on undisturbed sandy beaches. In migration, Least Terns from the Atlantic coast of North America pass through the Caribbean en route to winter grounds in South America. The species declined during the 19^th Century: hundreds of thousands were shot and their wing and tail feathers plucked for womenÆs hats. Humans can disturb the adults at nesting colonies or trample the well-hidden eggs. Oystercatchers, Ruddy Turnstones, crabs, as well as dogs, cats, rats, and mongoose may prey on eggs, young, and adult Least Terns. In many populations in North America, most birds now breed on flat, gravel-roofed buildings, since they are harassed by humans and animals on their beach nesting areas. The West Indian breeding population is estimated at 1,500-3,000 pairs.

RANGE: Breeds on beaches from New England and California south through Mexico to Honduras, and in the West Indies. It also breeds in inland rivers of the central USA, and on islands off Venezuela. The species winters off the Pacific coast of Mexico and the eastern coast of Central and South America to northern Argentina. It is not known where the Caribbean breeding population winters.

TAXONOMY: CHARADRIIFORMES; LARIDAE; Sterninae

Photo: G. Beaton


Photo: L. Miranda

References

Bent, A.C. 1921. Life histories of North American gulls and terns. Smithsonian Instit. U.S. National Museum Bull. 113. (Reprinted by Dover Press, 1963).

Bradley, P. and Y. Rey-Millet. 1985. Birds of the Cayman Islands. P.E. Bradley, George Town, Grand Cayman.

del Hoyo, J., A. Elliott, and J. Sargatal, eds. 1996. Handbook of Birds of the World, Vol. 3. Hoatzin to Auks. Lynx Edicions, Barcelona.

Erdman, D.S. 1967. Seabirds in relation to game fish schools off Puerto Rico and the Virgin Islands. Carib. J. Sci. 7:78-85.

Ehrlich, P.R., D.S. Dobkin, and D. Wheye. 1988. The birderÆs handbook: a field guide to the natural history of North American birds. Simon and Schuster/ Fireside, NY.

Harrison, P. 1983. Seabirds: an identification guide. Houghton Mifflin, Boston.

Harrison, P. 1987. A field guide to seabirds of the world. Stephen Greene Press, Lexington, MA.

Jackson, J. E. 2000. Distribution, population changes and threats to Least Terns in the Caribbean and adjacent waters of the Atlantic and Gulf of Mexico. Pp. 109-117 in Status and conservation of West Indian seabirds (E. A. Schreiber and D. S. Lee, eds.). Soc. Carib. Ornith., Special Pub. No. 1.

Lee, G. C. Puerto RicoÆs Least Tern status survey. El Pitirre 3(3):8.

Massey, B. W. 1998. Species and subspecies limits in least terns. Condor 100(1):180-182.

Saliva, J.E. 1994. Vieques y su fauna: Vieques wildlife manual. U.S. Fish & Wildlife Service, Boquerón, PR.

Thompson, B.C., J.A. Jackson, J. Burger, L.A. Hill, E.M. Kirsch, and J.L. Atwood. 1997. Least Tern (Sterna antillarum). in The birds of North America, No. 290 (A. Poole and F. Gill, eds.). Acad. Nat. Sci., Philadelphia, PA, and Am. Ornithol. Union, Washington, D.C.

Raffaele, H.A. 1989. A guide to the birds of Puerto Rico and the Virgin Islands. Princeton.

Raffaele, H.A. 1989. Una guía a las aves de Puerto Rico y las Islas Vírgenes. Publishing Resources, Inc., Santurce, PR.

Raffaele, H.A., J.W. Wiley, O.H. Garrido, A.R. Keith, and J.I. Raffaele. 1998. Guide to the birds of the West Indies. Princeton.

Schreiber, E. A. and D. S. Lee. 2000. West Indian seabirds: a disappearing natural resource. Pp. 1-10 in Status and conservation of West Indian seabirds (E. A. Schreiber and D. S. Lee, eds.). Soc. Carib. Ornith., Special Pub. No. 1.

Schreiber, E. A. 2000. Action plan for conservation of West Indian seabirds. Pp. 182-191 in Status and conservation of West Indian seabirds (E. A. Schreiber and D. S. Lee, eds.). Soc. Carib. Ornith., Special Pub. No. 1.

Voigts, D. K. 1999. Observations of a colony of roof-nesting Least Terns. Florida Field Nat. 27:103-108.

Wiley, J. W. 2000. A bibliography of seabirds in the West Indies. Pp. 192-225 in Status and conservation of West Indian seabirds (E. A. Schreiber and D. S. Lee, eds.). Soc. Carib. Ornith., Special Pub. No. 1.

Least Tern, Spanish text

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