Interior Least Tern Conservation

Interior Least Terns (Sternulla antillarum athalassos) were added to the federal list of endangered species in 1985 due to the population decline in the Great Plains and Mississippi Valley caused primarily by the loss of breeding habitat in this region.

Least Terns nest on the ground in bare sand, gravel, or shells, on dry mudflats, on salt plains, and in sand and gravel pits. The natural dynamics of prairie rivers maintain the sandbars that terns prefer for nesting. The water fluctuations that come with flooding and dry periods create bare sand bars, which terns find attractive for nesting.

However, much of the best breeding habitat has been lost or disturbed due to river damming, dredging, and straightening. By regulating the rivers, we have disrupted the flood cycle that scoured vegetation out of the riverbed and shifted sandbars in the wide river bottom. Regular flooding reduces the invasion of the riverbed by plants. However, floods during the breeding season can wash away tern nests, eggs, and chicks. Too little water in the river also can adversely affect the tern population. Not enough water in the river can result in fewer fish and consequently reduce the food source for terns. To be successful along Oklahoma’s rivers, breeding terns need a combination of suitable sandbars, favorable water levels, and sufficient food during the nesting season.

In addition to changes in natural river processes, terns also are threatened by increased disturbance by humans. Our rivers have become popular recreation areas, and the number of people on the river is increasing. ATV use in and along rivers has grown, hurting ground-nesting birds. Because terns build well-camouflaged nests on the bare sand, their simple nests are vulnerable to trampling by people, pets, and livestock. Even if we do not destroy the nest, human activity can keep parent birds away from the eggs and chicks, leaving them subject to overheating in the summer sun or predation by animals such as coyotes, crows, or raccoons.

What is being done to protect the Interior Least Tern?

Private landowners along the Canadian River in central Oklahoma safeguard colonies of Interior Least Terns on their property. They work with the Oklahoma Natural Areas Registry to voluntarily protect terns by allowing fencing of nesting colonies, discouraging human disturbance, restoring breeding and foraging habitat, and educating people who use the river. Learn more about the landowner conservation initiative and the least tern by reading a previous issue of our newsletter.

Along the Arkansas River in northeastern Oklahoma, the U.S. Army Corps of Engineers is restoring nesting habitat and building new islands from material dredged out of the navigation channel. In additional, the Corps is mindful of downstream tern colonies when discharging water from reservoirs. With the U.S. Fish and Wildlife Service, the Corps also helps to monitor the bird population on portions of the Arkansas, Canadian, and Red rivers.

Least Tern along Oklahoma’s rivers.

The Least Tern is the smallest member of the gull and tern family. The males and females are nearly identical in size and coloration. Distinguishing features of the Least Tern are: grey and white body color; black eye-stripe, cap, and nape; slightly forked tail; and narrow, pointed wings with a black edge. Juvenile terns that are less than 1 year old are white underneath, grey above, and have less well defined black markings (photo above). Nests are simply a shallow depression in the sand. Chicks and eggs are tan with brown speckles, providing excellent camouflage on the sandbars and river beds.

Look at pictures and read more at the Cornell Lab of Ornithology webiste.

How can I help the Least Terns in Oklahoma?

Don’t disturb nesting birds.

  • If birds seem agitated or take flight, you are too close!
  • Don’t ride ATVs on sandbars in nesting areas.
  • Keep pets on a leash when walking along river.
  • Keep livestock away form nesting areas.

Inform others about the Least Tern and how we can protect it.

Report bird or nest disturbance.

  • Call the Oklahoma Department of Wildlife Conservation: 1-800-522-8039
  • Call the U.S. Fish and Wildlife Service Law Enforcement Office: 1-405-715-0617

Become a volunteer monitor.