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Study finds eagles poisoned by lead exposure (07/02/2014)

The nation's eagles are dying from lead poisoning, according to a study of the bald eagle population conducted by the U.S. Fish and Wildlife Service including the Upper Mississippi River National Wildlife and Fish Refuge in the Upper Midwest.

The U.S. Fish and Wildlife Service began the study in 2011 and officials presented a report on the findings during four informational sessions throughout the Midwest. The refuge spans 261 miles through Illinois, Iowa, Minnesota and Wisconsin.

"Our beginning is the awareness,” said Ed Britton, Wildlife Refuge Manager, at an informational meeting Wednesday, June 18, at the Winona County Historical Society.

Researchers from the U.S. Geological Survey’s National Wildlife Health Center examined the livers of 168 dead eagles collected in the refuge, said Britton. “Forty-eight percent of birds we sent to them out of 168 had lethal levels of lead,” he explained.

Most birds begin with a small level of lead exposure in their systems, said Britton, because of lead paint and other environmental factors. However, he said lethal lead exposure is likely traced to lead ammunition used for hunting. Bald eagles are known to feed on gut piles and other animal parts left by hunters, and X-rays of the dead eagles showed lead fragments in their digestive tract. Some had whole bullets believed to have been ingested from animal refuse left by hunters after gutting deer.

Researchers also looked for lead poisoning signs in the eagle’s organs, including enlarged gallbladders and discolored gizzard lining.

“It’s tradition," Britton said of the ammunition believed to be the culprit. "Folks have always used lead [bullets]."

In the four-state area of the refuge, Britton said 600,000 deer are killed with firearms each year. That means there are as many as 600,000 gut piles left for scavenging as well. Researchers collected 25 gut piles left from hunters and found that 36 percent included lead fragments. In one case, a gut pile held 107 lead fragments, said Britton.

Once a lead bullet hits an animal, it shatters, leaving lead fragments inside.

“As [the eagles] are picking through, they’re really not discerning what they eat,” said Britton of the birds' eating habits.


Britton suggests using copper bullets, which are not poisonous and blow a clean hole through the animal.

“I’m a deer hunter, and if someone tells me that a copper bullet is going to kill a deer faster, I’m going to try it,” said Britton.

Britton said cost could be a factor for some hunters who might resist a change from lead to copper ammunition. Reports, however, have indicated the cost of non-lead ammunition has fallen in recent years.

Although research showed lead bullets negatively affected eagles, Britton said officials are still unsure whether the findings of the study represent an increasing trend of lead exposure over previous years. He said this might be a path for further research.

The study will be published in the Journal of Fishing and Wildlife. 


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