Least Tern (Sterna A. athalassos)

Home Browse Search

Least Tern (Sterna A. athalassos) Current Status: The interior least tern has been listed as endangered, both in Colorado and federally, since 1985. Today, the population of the interior least tern is believed to be between 4700 and 5000. In order to be a serious candidate for down listing to threatened status, the population needs to be at least 7,000. Biology: The interior least tern, whose natural longevity can exceed 20 years, is 8 to 9 inches tall with a wingspan of 20 inches. Both graceful and buoyant in flight, the bird is distinguishable by its glossy black crown, white forehead and underside, pale gray back and wings, and the bill that is yellow -orange with a black tip. The legs and webbed feet of the male are orange, while they are pale yellow on the female. Juvenile terns are darker gray and won't acquire the adult plumage until their second year. The interior least tern's diet consists of small fish of any species. The bird hunts it's pray by hovering 20 -30 feet above the water, searching for fish near the surface and then diving to catch the fish in their bill. Aerial displays by male terns are often a part of the courtship ritual. One such display is commonly referred to as the "fish flight," and involves a male tern carrying a small fish as he flies through the air with one or two possible suitors chasing him. The ground portion of the courtship ritual involves the male tern offering one of the two females the fish that he had been carrying. This helps secure the bond between the terns. Both sexes participate in the 21 -day incubation of the 2 or 3 eggs that are laid. Within a couple of days after hatching, the young are able to venture away from the nest. Although the young can generally fly within 3 weeks of hatching, both parents continue to be responsible for feeding the young long after they have fledged. The least terns are semi - colonial nesters. By nesting in quasi - colonies terns are afforded greater protection from predators. If a predator is detected by one of the birds in the colony, that bird will alert the others to the danger. The adult terns will then attack in a mob fashion by dive - bombing, shrieking at, and defecating on the intruder. Habitat: For breeding purposes, the interior least tern appears to thrive in habitat that is dependent on the presence of dry, flat, sparsely vegetated and exposed sandbars, within a river channel. The ideal river that would be consistent with optimal tern habitat should support flows that allow for a healthy fish population, but that do not increase enough to flood the sandbars. Migration: The interior least tern winters along the beaches of the Central American coast and along the northern coast of South America from Venezuela to Northeastern Brazil. The birds usually arrive at their breeding grounds (including Colorado) in early May. (In Colorado terns are most often seen around the La- Junta/Lamar area.) Fall migration usually begins in mid to late July and is concluded by early September. Recovery Efforts: Intensive research on habitat selection, reproduction, foraging habits and limiting factors has been conducted in several states where known breeding