Field Guide

Discover the diverse species of Oklahoma.

Interior Least Tern

The smallest North American member of the gull and tern family, least terns average 9 inches in length with a wingspan of 20 inches. These birds are slender and streamlined with a white breast and belly, a gray back, and long, narrow pointed wings. Adults have a black crown on the head. The tail is forked and the bill is straight, pointed and a deep yellow color.
Terns use a wide array of habitat types for foraging, including large rivers, lakes, ponds, and shallow wetlands. Conversely, nesting habitat is more specific; interior least terns construct nests on the ground and require open areas of sand and gravel that are largely devoid of vegetation.Historically, interior least terns nested along all of the large, sandy prairie river systems in Oklahoma. This included the Cimarron, Canadian, Arkansas, and Red rivers. Least terns that occur in Oklahoma are part of what is known as the “interior” population, which is considered distinct from the least terns that live throughout the coastal and estuarine habitats along the Gulf of Mexico and East Coast. A large part of this distinctiveness is the unique behavior and life history exhibited by interior least terns, such as their preferences of nesting habitat, foraging areas, and prey items.
Life Cycle: 
Least terns are migratory and only occur in Oklahoma only during the breeding season. Depending on habitat availability, tern nesting colonies can range from 2 to 70 pairs. Nests are constructed from late-May to mid-July and consist of a shallow depression on an open, sandy river bank. Both eggs and chicks are well camouflaged, helping them to remain hidden from predators. In fall, least terns migrate south to the Caribbean and the northern coast of South America. A long-lived species, least terns over twenty years old have been documented.
8.5-9 inches in length. 19-21 inch wingspan.
Conservation Status: 
The interior population of least tern was listed as a federally endangered in 1985, and was delisted due to recovery in 2021. Construction of large reservoirs altered flow regimes of many rivers and several sandbars that were historically used for nesting have been submerged. Seasonal flooding and subsequent scouring of river banks is required to build and sustain the sandbars needed for nesting. Least terns have positively responded to conservation efforts undertaken by several agencies and conservation organizations. Federal agencies such as the U.S. Army Corps of Engineers partner with the U.S. Fish and Wildlife Service by periodically constructing and maintaining artificial sandbars for nesting interior least terns throughout multiple river systems. Additionally, these agencies conduct multiple surveys each year to monitor nesting activity. At the time of its listing, the total population of the interior least tern was estimated at 1,400-1,800 birds. With range wide management and recovery efforts, the total population had increased to more than 17,000 birds by 2005. Through ESA Section 6 funding, the Wildlife Diversity Program has partnered with the University of Oklahoma’s Oklahoma Biological Survey to protect and monitor interior least tern nesting colonies along the Canadian River south of Norman, OK. Sandbars are marked with signs and flagging to increase awareness of the birds’ presence to recreational users of the river. Additionally, outreach to local landowners has played a large part in the protection of terns along this river. The Wildlife Diversity Program also periodically assists other agencies, such as the U.S. Army Corps of Engineers, with nesting colony surveys during the summer months.
Species of Greatest Conservation Need