Study links bald eagles and lead exposure

'The poisoning is often so acute that the eagle dies before it even manifests external signs'

A mature bald eagle flies around the water front at Pleasant Creek Recreation Area  north of Palo, Iowa. (Jim Slosiarek/
A mature bald eagle flies around the water front at Pleasant Creek Recreation Area north of Palo, Iowa. (Jim Slosiarek/The Gazette-KCRG)

A two-year study in which federal biologists examined 168 dead bald eagles from the Upper Midwest has again demonstrated the relationship between lead ammunition and lead exposure in bald eagles.

A series of four information sessions will be being Tuesday to share the results of the research.

“We just want to tell our story, raise awareness of the issue and encourage hunters to switch from lead to non-toxic ammunition,” said project leader Ed Britton, manager of the Upper Mississippi River National Wildlife and Fish Refuge’s Savanna District.

Britton said detectable concentrations of lead were found in 48 percent of the eagles’ livers, and 21 percent had concentrations considered lethal.

Most of the eagles also exhibited physical signs consistent with lead exposure, he said.

Britton and colleagues — U.S. Fish and Wildlife Service biologists Sarah Warner, Mike Coffey and Drew Becker — began collecting dead eagles from Iowa, Minnesota, Wisconsin and Illinois in 2011. Most of them were contributed after recovery by conservation offices from several agencies.

They examined 58 eagles in 2011 and 110 in 2012, with the majority coming from Iowa and Wisconsin.

After conducting necropsies, they sent the livers to the U.S. Geological Survey’s National Wildlife Health Center in Madison, Wis., for analysis.

Although most eagles showed no visible external signs of lead poisoning, internal examination of organs showed clinical signs and gross lesions of lead poisoning that included distended and bile-engorged gallbladders, Britton said.

“The poisoning is often so acute that the eagle dies before it even manifests external signs,” he said.

Britton said their findings prompted a secondary investigation into the potential sources of lead in the environment.

Recognizing that eagles feed heavily on carrion during the winter when fish are not readily available, the researchers collected and X-rayed 25 deer gut piles recovered from the Lost Mound unit of the Upper Mississippi refuge in northwest Illinois, where managed deer hunts are conducted.

The X-rays showed that 36 percent of the gut piles contained from one to 107 lead fragments per offal pile, Britton said.

In addition to gut piles, field-dressed deer carcasses are often left behind by hunters, and many wounded deer die unrecovered by hunters, providing additional sources of lead-contaminated food.

The magnitude of the problem is illustrated by the fact that during the 2012-13 season gun hunters killed about 637,000 deer in the four states included in the study.

“Here we have independent researchers reaching the same conclusions as everyone else who has studied lead poisoning in eagles,” said Kay Neumann, executive director of Save Our Avian Resources.

“The really scary part,” she said, “is that the Upper Mississippi is the focal point for wintering eagles in North America.”

Lead-contaminated gut piles contain multiple lethal doses so that several eagles could die from feeding on one gut pile, she said.

Similar to Britton and other colleagues, SOAR advocates a voluntary approach to replacing lead ammunition with non-toxic metals.

“Hunters don’t want to hurt eagles. They love being able to watch them while they are hunting. I think we can get hunters to switch on their own,” she said.

Britton and Neumann say deer hunters could switch to copper projectiles without diminishing their effectiveness or greatly increasing their costs.

Raptor expert Bob Anderson, a leader in the successful effort to return peregrine falcons to their historic Mississippi River bluffs and the godfather of the famous Decorah eagles, is less patient.

“I think we should outlaw lead ammunition,” he said. “Voluntary switching is not happening fast enough.”

Lead ammunition’s lethal threat to raptors has been well documented since the 1970s, yet eagles still are dying of lead poisoning, Anderson said.

“It’s so preventable,” he said.

During the last 15 years, Anderson said he has participated in the recovery about two dozen lead-poisoned eagles.

“Any hunter who witnessed the suffering of a lead-poisoned eagle, staggering around blind and crying in pain, would immediately switch to non-toxic ammunition,” he said.

The upcoming information sessions will be Tuesday at the Refuge Visitor Center in Thompson, Ill; Thursday at the Community Center in Prairie du Chien, Wis.; June 18 at the Winona Historical Society in Winona, Minn; and June 19 at the Refuge Visitor Center in Onalaska, Wis. All meetings run from 6 to 8 p.m.

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