North Dakota Field Office
Mountain-Prairie Region
Least Tern
(Sterna antillarum)

leaves

least tern by US Fish & Wildlife Service
by US Fish & Wildlife Service)

Official Status:Endangered (North Dakota).  Endangered species are animals and plants 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 in North Dakota.

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 over 8,000 least terns in the interior population.  Birds from the interior population winter along the Gulf of Mexico and on Caribbean Islands.  In North Dakota, the least tern is found mainly on the Missouri River from Garrison Dam south to Lake Oahe, and on the Missouri and Yellowstone Rivers upstream of Lake Sakakawea.  Approximately 100 pairs breed in North Dakota.

Habitat:  In North Dakota, the least tern utilizes sparsely vegetated sandbars on the Missouri and Yellowstone Rivers.  Birds nest, raise young, and relax on barren river sandbars.

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" across, on barren, sandy 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" in length.  Unlike gulls, terns will dive into the water for small fish.  The body of least terns is predominately 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 dams, river flows are often managed in a nonhistoric fashion, not conducive to the creation and maintenance of sandbars with sparse vegetation.  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 North Dakota 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.

interior least tern by US Fish & Wildlife Service
Photo by US Fish & Wildlife Service

Last updated: February 19, 2013