Endangered birds’ hatch numbers dip

SIOUX FALLS, S.D. — Thunderstorms and the loss of shoreline habitat combined to reduce the hatch success of two bird species on the Missouri River system this summer.

Areas along the river and reservoir system from Sioux City, Iowa to Fort Peck, Mont., are designated as critical habitat for the piping plover, a threatened species, and the interior least tern, an endangered species.

The Army Corps of Engineers is required under a 2003 Amended Biological Opinion from the U.S. Fish and Wildlife Service to provide nesting habitat for the birds, which nest on sandy shorelines and sandbars. The corps monitors them during their summer stay, using 30-40 seasonal employees who count adult birds, nests, eggs and chicks.

“It was a poor year for both species, both from a standpoint of the number of adults and the number of fledglings,” said Greg Pavelka, wildlife biologist at Yankton and manager of the corps’ plover and tern monitoring program.

A final count showed 425 plover chicks and 278 tern chicks survived and headed south to wintering grounds. Plover reproduction was down 37 percent from 2008. Tern reproduction fell 28 percent.

The corps creates nesting areas to replace those created naturally before dams and reservoirs altered the river’s flow.

The least tern and piping plover — both roughly the size of a robin — prefer vegetation-free sandbars for their nests. While both birds nest elsewhere, the Fish and Wildlife Service designated areas along the Missouri River as critical habitat for the piping plover.

An endangered species is one that is in danger of extinction throughout all or a significant portion of its range. A threatened species is one that is likely to become endangered in the foreseeable future.

The number of adult plovers was down about 30 percent on Lakes Oahe and Sakakawea. Both reservoirs refilled after years of drought, wiping out shoreline nesting that plovers prefer, forcing some of them to other habitat outside the corps’ jurisdiction, Pavelka said.

The population of adult terns was down about 10 percent on the upper stretches of the Missouri River system and mostly unchanged at the lower end.

By late August both have migrated south.

Crews counted 897 adult plovers and 2,091 plover eggs this summer. The tern count was 706 adults and 1,220 eggs.

Predators like mink, raccoons and great horned owls are a threat to eat eggs or kill chicks.

And a July 8 storm with 70 mph winds and 2 inches of rain in 30 minutes hit an area below Yankton where the corps has been creating sandbars for nesting habitat as part of the recovery program.

“On one of the sandbars, crews had previously counted over 80 chicks. When they came back two days after the storm, there were only 30 chicks to be found,” he said.

Storms also hit nesting areas below Garrison Dam in North Dakota. Sometimes, the birds will try to nest a second time if the first nesting is unsuccessful, but if it’s too late in the summer the birds are already thinking of migrating south and will forgo re-nesting.

Plovers winter on the southern U.S. coast, in the West Indies and the Bahamas. Terns head to South America, he said.

Research on banded birds has found up to 85 percent of adult birds will to return to the same nesting area. Up to 30 percent of the chicks will return. Given a 50 percent mortality rate in the first year of life, “that’s still a fairly high number,” Pavelka said.

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