Full reservoirs reduce nesting areas

SIOUX FALLS, S.D. — A spring snowmelt that brought two Dakotas reservoirs back to normal levels is chasing away threatened and endangered birds that nested on the shore during nearly a decade of drought.

The piping plover, listed as a threatened species, and the interior least tern, an endangered species, use sandy shore or sandbars for nests. Sandy areas were plentiful when Lakes Oahe and Sakakawea dropped by 30 feet or more during nine consecutive years of below-normal runoff.

But both Missouri River reservoirs are at normal levels this year after heavy snow in the Montana mountains melted and drained into them in April and May. The loss of nests on the reservoirs’ shores, combined with the destruction of nests below Gavins Point Dam at Yankton by rain and hail, could mean fewer plovers and terns will hatch this summer.

Lake Oahe, which extends 260 miles from Pierre to Garrison Dam near Riverdale in North Dakota, is 21 feet higher than a year ago. Lake Sakakawea, which stretches another 178 miles from the Garrison Dam to Montana, is 19 feet higher than last July.

Plovers and terns nest elsewhere, too, but areas along the Missouri River are designated as critical habitat. The Army Corps of Engineers is building sandbars for the birds and monitoring them along the Missouri River system from Sioux City, Iowa, to Fort Peck, Mont.

The plover population nationwide was estimated at 8,092 adults in 2006, the corps said. Least terns were estimated at about 85,500 in the U.S. in 2006, with 17,500 of them on interior rivers. Among those rivers, the Missouri River system had the most, with 908 adults.

It’s not known yet how many chicks will hatch this year, but there were fewer adult birds on Oahe and Sakakawea, said Greg Pavelka, wildlife biologist and manager of the corps’ plover and tern monitoring program.

The 2008 census counted 363 adult plovers on Sakakawea and 281 on Oahe. This year’s count was 85 on Sakakawea and 154 on Oahe.

Also last year, there were 14 least terns on Sakakawea and 111 on Oahe. This year’s survey counted 15 on Sakakawea and 71 on Oahe.

The northernmost reservoir, Fort Peck in Montana, doesn’t attract many birds, Pavelka said.

There is some indication that plovers, which were forced off Lake Sakakawea by the rising water, renested on sandbars in the river between Garrison Dam and Lakes Oahe, he said.

The lower river system below Fort Randall Dam at Pickstown near the Nebraska border also had fewer terns, possibly because of higher water releases from the dam that eliminated shallow-water areas where the birds usually feed.

“Those shallow areas are now anywhere from 1 to 2 feet deeper with the higher releases,” Pavelka said.

“I do remain hopeful that we’re going to have good nest success and hopefully good chick success below Garrison and on the constructed sandbars, but it’s too early to tell,” he added.

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