[order] Charadriiformes | [family] Sternidae | [latin] Sterna antillarum | [UK] Least Tern | [FR] Petite Sterne | [DE] Amerikanische Zwergseeschwalbe | [ES] Charrancito Americano | [IT] Fraticello americano | [NL] Amerikaanse Dwergstern

Amerikaanse Dwergstern determination

copyright: Don DesJardin

The least tern is the smallest American tern, weighing about 1 ounce (28 gm) and measuring about 9 inches (23 cm) in length. It is identified in spring and summer by a white forehead contrasting with a black crown and nape. Its body is slate grey above and white below, with the pointed wings and forked tail characteristic of most terns. The bill and feet are yellow. Wingbeats are uniquely rapid and the black leading edge of the outer wing is conspicuous in flight. Immature least terns have upper parts which are mottled white and dark brown.

The least tern breeds on broad, level expanses of open sandy or gravelly beach, dredge spoil and other open shoreline areas, and more rarely, inland on broad river valley sandbars. In an unusual case, 20 pairs nested on the roof of a city auditorium in Pensacola, Florida in 1957, and have continued to do so annually.

Least Tern has three breeding populations that have been described as distinct subspecies: along the Atlantic and Gulf Coasts from New England south through the Caribbean (S.a. antillarum); along rivers in the central United States (S.a. athalassos); and on the Pacific Coast from San Francisco Bay to western Mexico (S.a. browni).
The least tern has a nearly worldwide distribution. In the Western Hemisphere, it breeds on the Pacific Coast from central California to Peru, inland along the Colorado, Red, Rio Grande, Missouri and Mississippi river systems, on the Atlantic Coast from Maine to Argentina, and along the Great Lakes in Michigan, Minnesota, Wisconsin and Ohio. Migrants mainly occur on Long Island's outer coast and rarely on the lower Hudson River. This species winters from the Gulf Coast and Central America south to Peru and Brazil.

Least terns feed mostly on small fish caught by skimming the surface of the water or by making dives from the air. Banding studies have shown individuals living up to 21 years.

This species has a large range, with an estimated global Extent of Occurrence of 470,000 kmē. It has a large global population estimated to be 65,000-70,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Least Terns generally nest and breed in colonies. In courtship, a male carrying fish will fly up, followed by the female; both then glide down together. Their nests are shallow scrapes on open sand, soil, or pebbles, occasionally lined with pebbles or grasses. Although they prefer sandy beaches for nesting, they occasionally utilize flat, gravel-covered rooftops instead. Least Terns lay 1 to 3 buff or pale green eggs with dark blotches. Both sexes build nests, incubate the eggs, and care for the young. Incubation lasts slightly over 3 weeks. The downy chicks are able to walk soon after hatching, with their eyes open. A few days after hatching, they move to short vegetation nearby. They begin to fly at just under 3 weeks of age, and may remain with their parents for up to 3 months.

Highly Migratory. Pacific breeders arrive late Apr, and return in Aug to coasts of W Mexico and Central America. Interior and E birds migrate to Caribbean and N South America, wintering mainly off Brazil. Substantial inter-colony exchange from year to year, even when original colony persists. Nominate race accidental inland.