Volunteers sought to monitor state’s burgeoning population

The exponential growth of bald eagles in Iowa has exceeded the Department of Natural Resources' ability to monitor the expansion and the success of the nests.

To help track the proliferation, the DNR is looking for people to “adopt” one of 54 selected eagle nests and become an official monitor.

“We hope in the next two years to start getting a better handle on Iowa's eagle nesting success in Iowa, and we hope to get some help with that from Iowans,” said DNR wildlife diversity biologist Stephanie Shepherd, who is coordinating the effort.

From just one in 1977, the number of active bald eagle nests in Iowa has increased to at least 254 in recent years. Biologists attribute the turnaround to the 1972 banning of DDT, a pesticide that fatally thinned raptors' eggshells.

“In the 1990s, we had a pretty good idea of where all the eagle nests were and what was going on with them,” Shepherd said. With the subsequent rapid increase, “the nests we are aware of are likely just the tip of the iceberg, and we have little data on how successful and productive those nests are.”

The removal of the bald eagle from the federal endangered species list and its upgrading in Iowa from “endangered” to “special concern” does not mean the birds' welfare can be taken for granted, Shepherd said.

Besides dwindling habitat, eagles face dangers ranging from lead poisoning and collisions with power lines and vehicles to being shot by thoughtless people, she said.

Though eagles now nest in 86 of Iowa's 99 counties, including Linn and Johnson, well more than half of Iowa's eagle nests are in five counties bordering the Mississippi River. A high percentage of those nests are within the Upper Mississippi National Fish and Wildlife Refuge, whose personnel track eagle-nesting success.

Refuge specialist Tim Loose said there were 136 eagle nests last year in the refuge's McGregor District, which includes the river and a narrow band on each side from Genoa, Wis., to Dubuque, a distance of a little more than 100 miles.

The refuge, he said, has in abundance the three things eagles value most in a nesting site: water, which is essential to eagles' favorite food source, fish; trees large enough to hold their potentially 1-ton nests; and solitude.

While eagles prefer solitude for their nest sites, they have demonstrated increasing tolerance of human activity, as well as proximity to other eagle nests.

“We have seen nests built around farmyards where people come and go all the time,” Shepherd said. Eagles also have built nests along rivers within the city limits of Des Moines, Ames and Cedar Rapids.

Loose said he does not believe Iowa eagles have come close to using up all available nest sites. “We used to think eagle nests had to be at least a mile apart, but we see them within 200 yards of each other,” he said.