Least Tern

Sternula antillarum

(c) Glen Tepke
  • LARIDAE
  • Gulls, Terns, and Skimmers
  • Charadriiformes
  • Charrán mínimo
  • Petite sterne
Introduction
The Least Tern's name reflects its diminutive size. Despite the fact that it is the smallest of the terns, it commonly keeps company with larger terns at roosting and foraging sites. It may be seen assertively defending its nest by diving at intruders, calling shrilly while flying low over the water, or hovering above before plunging in to catch tiny prey.
(c) Margo Zdravkovic
Appearance Description
These tiny terns weigh about 1.5 ounces (42 grams), and measure about 9 inches in length, with a wingspan of 20 inches. Both sexes look alike, with grayish-white body; relatively long, narrow wings; yellow legs; a short notched tail; and a yellow bill unique among North American terns.
Range Map
Courtesy Kenn Kaufman
Range Distribution
Least Terns breed along both the Atlantic and Pacific coasts southward to Mexico, Central America, and the Caribbean. Inland populations breed along the Missouri, Ohio, and Mississippi Rivers, and other scattered inland locations. They winter along Mexican coasts south to South America.
 
A legend for the range map to the right can be found here.
Habitat
Least Terns most often inhabit sandy or gravelly coastal areas adjacent to the shallow water where they feed; they are also found along inland river banks and lakes with broad exposed sandbars.
Feeding
Small fish, crustaceans, and insects are the preferred foods for Least Terns; small mollusks and marine worms are eaten as well. Least Terns forage over water, hovering briefly before plunging in to catch tiny prey just below the surface; they sometimes dip to pluck prey from the surface or to catch insects in flight.
Reproduction
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.
Migration
Least Terns vacate North America and northern Mexico in the fall, moving to tropical waters further south to Central and South America; Least Terns from the northern U.S. migrate the greatest distances. The California subspecies winters in southern Mexico; wintering areas for other U.S. breeding populations are largely unknown.
  • 67,550
  • 67,550
  • Subspecies Endangered
  • moderate population declines; small population size
Population Status Trends
Least Terns have the unfortunate distinction among North American terns of being classified for protection throughout much of their North American range. The Least Tern is a USFWS Bird of Conservation Concern, a continentally threatened species, and classified as "Threatened," "Endangered," or a "species of concern" in most states. Christmas Bird Count (CBC) and Breeding Bird Survey (BBS) data both indicate a decline for this species.  Although widespread and common in some places, many populations are endangered because the beaches needed for nesting are much in demand for human recreation and residential development. Inland, water fluctuation from dams often flood nesting sites along rivers.
Conservation Issues
Least Tern populations declined rapidly beginning in the late 1800s, due to feather hunting and egg collecting; they have been in flux ever since. Populations rebounded following passage of the 1916 Migratory Bird Treaty Act. However, since the 1940s, the nesting sites of many interior populations have been destroyed by flooding behind dams, channelization, and untimely water releases. Further population declines in the 1950s to 1970s were attributed to pesticide use and human disturbance of nesting habitats. Increased conservation efforts since the 1980s have helped restore some populations. However, recreational, industrial, and residential development in coastal breeding areas continues to diminish many populations.
 
Because of the endangered status of California and interior Least Terns, various agencies have monitored these populations in recent decades. But because Least Terns are relatively long-lived, reproductive problems are not immediately obvious. Thus, in addition to numbers, it is vital to monitor reproductive success. While Least Terns adapt to degraded habitat by readily shifting breeding sites, they seem most productive at sites with long-term stability. To encourage Least Terns to nest on protected habitat, they are sometimes lured to safer sites with decoys and recorded calls—techniques developed by Audubon's Seabird Restoration Program.

Conservation status can be challenging to assess because Least Terns are highly mobile, subspecies are almost identical, and few leg-banded terns have been recovered or re-sighted. Protection of interior populations requires rivers to be maintained at levels that avoid flooding natural nesting areas wherever possible. More research linking the various breeding populations to their respective wintering areas is needed, as are comprehensive management plans wherever declining populations exist.

What You Can Do
Never leave fishing lines, lures, or hooks on beaches; entanglement is usually lethal to terns.
 
Don't dump garbage or fishing bait which feeds competing gulls.
 
Don't disturb nesting tern colonies when hiking or landing boats; prevent dogs and children from disturbing them. When parent terns abandon their nests, eggs or chicks can overheat or become wet and chilled, often resulting in death.
 
For actions you can take, including Audubon activities, please visit our resources page.
More Information
Learn about seabird restoration projects for Least Terns and other seabirds at: http://www.projectpuffin.org
 
Visit our resources pagefor more information about this species.
Natural History References
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.). The Academy of Natural Sciences, Philadelphia, PA, and the American Ornithologists Union, Washington, D.C.
 
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, Inc., New York, 2000
 
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996
Conservation Status References
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.). The Academy of Natural Sciences, Philadelphia, PA, and the American Ornithologists Union, Washington, D.C.
 
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, Inc., New York, 2000
 
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996