INTERIOR LEAST TERN

Endangered Species Guidesheets Main Menu

2/97

INTERIOR LEAST TERN

Sterna antillarum athalassos

The Interior least tern is a bird that forages over large rivers and nests on open expanses of sand or gravel on islands in the river. Reservoir construction along the Mississippi and Missouri rivers has reduced, and sometimes eliminated, habitat essential for reproduction. Nesting colonies are threatened by human disturbance. The Interior least tern is listed ENDANGERED by the Missouri Department of Conservation and ENDANGERED by the U.S. Fish and Wildlife Service.

Identification

[drawing of interior least tern] Least terns are the smallest of American terns, averaging 8 1/2 to 9 1/2 inches long, with a wingspan of about 20 inches. Like all terns, they are slender with long, narrow wings, a forked tail, and a pointed bill. Interior least terns are black-capped with a white forehead, a black-tipped bill, gray and black wings, a pale gray back and tail, and a white belly.

Males have brighter feet and bills (bright orange or yellow) than females (pale or dull yellow). Juveniles tend to have darker plumage and bills than adults and often have a dark eye stripe on their white forehead.

There are two other races of the least tern in the United States: the Eastern (or Coastal) least tern (var. antillarum) and the California least tern (var. browni). Neither of these subspecies are found inland.

For a technical description of this animal, refer to:

Robbins, C.S., B. Bruun, and H.S. Zim. 1983. A Guide to Field Identification: Birds of North America. Western Publishing Company. New York, NY. 360 pp.

Life History

Females begin laying eggs in late May and produce one to four pale to olive-buff eggs. Eggs are speckled or streaked with dark, purplish-brown to blue-gray markings. Incubation generally lasts 20 to 25 days.

Hatchlings reach the fledgling stage in three to four weeks but remain with their parents until migration. Pre-fledgling mortality rates are high, but adults may live 10 years or more.

They feed almost entirely upon small fish and require shallow water areas near their nesting sites that provide abundant small fish populations. Sites for breeding and nesting are generally bare or sparsely vegetated.

Nests within the colony, or ternery, are scattered, and only the area directly around the nest is defended. Terns choose sites that are well-drained and away from the water line. Nests, or "scrapes," are made by scraping a depression in the sand or gravel. The scrape may be lined with pebbles or small shell fragments.

Interior least terns migrate in small loose flocks, arriving in Missouri from late April to mid-May. They leave for their wintering areas in August and September. It is unknown where the terns go during the winter. However, unidentified terns have been found during the winter in Central and South America.

Habitat and Distribution

Natural habitat for terns includes islands, beaches, and sandbars, but as these areas have become rare, terns have been forced to use dredge islands, dikefields, fly-ash lagoons, sandpits, and gravel roads on top of levees.

Interior least terns are generally restricted to larger meandering rivers with a broad floodplain, slow currents and greater sedimentation rates, which allow for the formation of suitable habitat. Interior least terns experience the greatest nesting success on sand or gravel bar islands because predation by terrestrial predators is reduced.

In Missouri, Interior least terns used to nest along the Missouri River and southern half of the Mississippi River, especially where the two rivers joined. They are presently found only in the southeast portion of the state along the Mississippi River in Pemiscot, New Madrid, Scott, and Mississippi counties.

Cause of Historic Decline

Channelization, irrigation, and the construction of dams, levees, reservoirs, and dikes have eliminated most of the sandbars suitable for tern nesting. Unpredictable and poorly timed water discharge from dams have flooded terns' nests and nesting sites, and allowed woody vegetation to encroach on remaining sandbars.

Current Threats to Interior Least Terns

Loss of breeding and nesting habitat Damage to nests and destruction of nesting sites by dam water discharge, vegetative encroachment, and loss of nesting islands are the primary concerns for long-term survival of the least tern.
Human disturbance Recreational activities on sandbars and sand and gravel pits disrupt tern breeding. ATV's, hiking, picnicking, boating, and swimming on or near sandbars with tern colonies or artificial nesting sites can result in nest failure and high mortality of young terns.
Predation Predation on tern eggs and young by feral cats and dogs, coyotes, crows, laughing gulls, and foxes can be a serious problem. Unattended pets and garbage left behind on sandbars can encourage the problem.

Protection and Management: Steps Toward Recovery

There are fewer than 10 nesting colonies in Missouri. All are on sand islands in the lower Mississippi River of the bootheel region. Three of these islands are managed by the Department of Conservation, the rest are on private land. Since these areas have little use other than recreation and wildlife most landowners are pleased to assist with tern recovery efforts.

All of these sites are affected by river management that reduces water levels to expose the nesting sites during the summer months. Participation from the U.S. Army Corp of Engineers is essential to tern restoration in the Mississippi River.

Compatible river management is essential for the full recovery of the least tern. Unfortunately, there is little a private landowner can do to influence how a river flows or when a dam releases water. Wise timing of discharge from dams is needed to prevent nest flooding and to promote "scouring" of sandbars to remove woody vegetation. Private landowners who own sandy islands used by terns can help by implementing the following suggestions.

Waterway management In areas where sandbars have been overwhelmed by woody vegetation, removing the vegetation may benefit the tern by providing nesting habitat. Removing vegetation by hand or by using chemicals may be necessary each year and should be done instead of mowing. Notched wing dikes that cause sand to deposit downstream can create new nesting islands.
Human disturbance Avoid disturbing nesting terns or their young. People should avoid sand islands where least terns are nesting from mid-May through mid-August. In Missouri, tern nesting sites are posted as seasonal refuges. Control pets near nest sites. Hiking, boating, swimming, picnicking, and camping should be done away from tern colonies to avoid impact. If necessary, fences can be erected around terneries during the breeding season, particularly to regulate the use of ATV's.
Predator control Garbage and litter should be removed from sandbars so predators are not attracted to them. The Missouri Department of Conservation can build predator exclosures around terneries to control predation of chicks and eggs, and shelters can be constructed for tern chicks using snow fence slats.

Missouri and federal law prohibits the importation, transportation, sale, purchase, taking or possession of birds on the State or Federal lists, as well as their eggs and nests.

For more information on the Interior least tern, or to report sightings of this species, contact:

Endangered Species Coordinator or Wildlife Ecologist Missouri Department of Conservation Natural History Division P.O. Box 180 Jefferson City, MO 65102 (573) 751-4115

Endangered Species Guidesheet