Least Tern (Sterna antillarum)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Snowy Plover, Piping Plover,
Killdeer, American Avocet, Black-necked Stilt, and Spotted Sandpiper.
Distribution: Least Terns nest along the East, West, and Gulf coasts, and inland along the
Missouri and Mississippi river drainages. In Physiographic Area 36 in Colorado, they nest only
on reservoirs in the vicinity of the Arkansas River, between Las Animas and Lamar.
Habitat Requirements: Least Terns nest on sandbars, islands, beaches, and alkali flats with little
or no vegetation, although they will tolerate more vegetation than the plover species. Vegetation
provides thermal and hiding cover for chicks later in the season. Nests are often located within 20
m (65 ft) of water. Nesting success is higher on islands than on the mainland, probably due to
restricted access by terrestrial predators.
Ecology: These semi-colonial terns place their nests from a few meters to hundreds of meters
apart from one another. Adults arrive in Colorado in mid May and initiate nesting between late
May and early July. Most young leave the nest by mid August, and most birds leave the state by
mid September. Least Terns winter in Central and South America. They feed primarily on fish,
but may also take terrestrial and aquatic invertebrates.
Management Issues and Conservation Recommendations: Disturbance or destruction by
humans and domestic animals often leads to nest failure. Least Terns will accept artificial islands
for nesting, but they will not use freshly made islands until the soils have settled and become
stable. Management efforts, including alteration of water management schemes and habitat
manipulation, should follow the guidelines of the federal and state recovery plans (Sidle and
Harrison 1990, Slater 1994).
Status and Reasons for Concern: This species is listed as Endangered at the federal and state
(Colorado) levels. Fewer than 50 pairs breed in Colorado. Due to its small numbers and limited
range, this species is not monitored by the BBS. This species is monitored by CDOW and
Biological Objective: Increase the species' distribution and abundance, based on results of
CDOW censuses or other monitoring programs.
Selected References: Andrews and Righter 1992, Kingery 1998, Thompson et al. 1997.