Least Tern recovery project shows promise

Endangered birds breed on floating habitat at Riverlands

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ST. LOUIS, MO - Twelve pairs of federally endangered Interior Least Terns, Sternula antillarum athalassos, have nested on an artificial island designed to substitute for seasonal river sandbars. The island was created on barges within the Riverlands Migratory Bird Sanctuary, where the emerging Audubon Center at Riverlands will be sited. The Least Tern is listed as "red" (facing major conservation threats) on the 2007 Audubon WatchList.

Interior Least Terns formerly nested along the Mississippi River well into Iowa, but due to disruption of the upper Mississippi River system by locks and dams built to facilitate barge travel, natural dynamics that created these successional sandbar islands are all but lost on the upper portions of the river. On the Mississippi, Interior Least Terns now nest only below the confluence of the Missouri River, where natural sandbar development still occurs. A 2008 population survey counted 12,183 adult Interior Least Terns in 59 nesting colonies between Cape Girardeau, MO, and Baton Rouge, LA. More than 60 percent of the total Interior Least Tern population nests along this portion of the Mississippi River.

One potential temporary solution to habitat loss on upper stretches of the river is to install artificial nesting areas for the terns. In 2002, the St. Louis Audubon Society worked with the U.S. Army Corps of Engineers Rivers Project Office to construct a permanent island above the Missouri River confluence at the Riverlands Migratory Bird Sanctuary. Although several Interior Least Terns were observed around the area, none attempted nesting on the island. This may be because the island is too close to the main shore, where predators live, making it undesirable as nesting habitat for the terns.

In April 2009, the Corps' Rivers Project Office placed two floating pontoon barges in Ellis Bay, a backwater of the Mississippi River above the Melvin Price Locks and Dam at Alton, IL. The two barges are lashed together and topped with approximately five inches of a sand/gravel mix, providing 1,500 square feet of nesting habitat. Pairs of Least Tern decoys and speakers projecting Least Tern calls were placed on the barges in an attempt to attract terns to the site.

By mid-May, Interior Least Terns were seen landing on the barge, and on July 7, observers counted 12 nests holding a total of 30 eggs. On July 24 and August 6, biologists from the Corps, Illinois Department of Natural Resources and Illinois Natural History Survey banded a total of 20 hatchlings. An additional three hatchlings may have fledged before the crew could arrive to band the young terns. Six eggs remained on the habitat project on August 6, so more birds may fledge from the site before the end of the season.

Initial results from the project indicate that if satisfactory habitat is provided in the historic breeding range of the Interior Least Tern, successful breeding colonies could return to these areas.

Easily visible from the Riverlands sanctuary, the project has attracted attention from visitors, offering the Corps and Audubon continuing opportunities to educate the public on the importance of healthy river ecosystems.

"There is still a lot to learn and understand from this project, but for now we feel that the experimental project has been successful," says Sarah Miller, a Corps biologist. "We will continue to monitor the island until the last tern has fledged and the birds have migrated south."