Threatened and Endangered Species Least Tern Sterna antillarum Fact
Threatened and Endangered Species: Least Tern Sterna antillarum
OFFICIAL STATUS: Endangered—Montana. 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
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
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.
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