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Threatened and Endangered Species Least Tern Sterna antillarum Fact Sheet

Least Tern Sterna antillarum

OFFICIAL STATUS: Endangered. Endangered species are species that are in danger of extinction throughout all or a significant portion of their range. It is unlawful to kill, harm, or harass endangered species.

LISTED: 50 Federal Register 21792; May 28, 1985 (interior population of the least tern).

HISTORICAL STATUS: Historically, the least tern was found on the Atlantic, Gulf of Mexico and California coasts, and on the Mississippi, Missouri, and Rio Grande river systems. It was found throughout the Missouri River system up to the lower Missouri in Montana.

PRESENT STATUS: The interior population of the least tern presently breeds in the Mississippi, Missouri, and Rio Grande river systems. The birds usually stay in close proximity to the rivers. Census data indicates that there are presently about 2,500 breeding pairs of least terns in the interior population. Birds from the interior population winter along the Gulf of Mexico and on Caribbean islands. In Montana, breeding least terns occur on the Yellowstone River and Missouri River between Fort Peck Reservoir and North Dakota. The western most nesting sites known are found on islands and shorelines within the Charles M. Russell National Wildlife Refuge.

HABITAT: In Montana the least tern utilizes sparsely vegetated sandbars on the Yellowstone and Missouri rivers. Birds nest and raise young on barren river sandbars. Nesting areas must be near shallow water feeding areas with good minnow populations.

LIFE HISTORY: The breeding season for the interior population of the least tern lasts from May through August. The peak of the nesting season occurs from mid-June to mid-July. Nests are bowl shaped depressions, about 4 inches across, on barren, sandy or pebble areas. Least terns nest in colonies where the nests can be as close as a few feet apart. A typical clutch contains 2 to 3 eggs and takes about 24 days to hatch. Both parents incubate the eggs and feed the young. Young are able to fly in about 21 days. Least terns typically live 1 to 5 years. Terns forage for small fish in the river and nearby wetlands.

AID TO IDENTIFICATION: Least terns are the smallest member of the gull and tern family. They are approximately 9 inches in length. Unlike gulls, terns will dive into the water for small fish. The body of least terns is predominantly gray and white with black streaking on the head. Least terns have a forked tail and narrow pointed wings. Least terns less than a year old have less distinctive black streaking on the head and less of a forked tail.

REASONS FOR DECLINE: The interior population of the least tern has declined due to loss of habitat from dam construction and river channelization on major rivers throughout the Mississippi, Missouri, and Rio Grande river systems. Because of the dams, river flows are often managed in a way that is not conducive to the creation and maintenance of vegetation-free sandbars. Human disturbance is also a problem. Cold water temperatures due to reservoirs may affect the quantity of forage fish available.

RECOMMENDATIONS: Avoid sandbars that have least terns present. Adult birds with eggs or young nearby will squeal loudly while circling overhead, and may swoop down at the intruder. Leave the area immediately.

COMMENTS: Biologists are uncertain about whether least tern populations from the Atlantic coast, California coast, and interior North America are separate subspecies or simply separate populations. For purposes of the Endangered Species Act, the U.S. Fish and Wildlife Service has assigned the endangered status to the interior population of the least tern. The California population of the least tern has been listed as endangered since 1970. The Atlantic population is not listed. Least terns in Montana will often be found sharing sandbars with the piping plover, a threatened species.

REFERENCES: Interior Population of the Least Tern Recovery Plan by U.S. Fish and Wildlife Service, 1990.

Threatened and Endangered Species: Least Tern (PDF; 106 KB)