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Biologists Find Correlation Between Bald Eagle Deaths and Lead Shot

Peter Eyerhalde
Iowa State University

Lead shot used by deer hunters in the Upper Midwest is getting into the digestive tracts of bald eagles, according to a two-year study by the US Fish and Wildlife Service. 

Researchers found 36 percent of leftover deer carcasses in a four-state national wildlife refuge contained lead fragments, which scavenging eagles use as a food source. 

The Upper Mississippi River National Wildlife and Fish Refuge extends from Wisconsin and Minnesota into Illinois and Iowa. Thousands of hunters visit each year to shoot deer and other game, and many use lead-based ammunition. But intensive review of 168 bald eagle carcasses detected concentrations of lead in at least half the birds.

Tina Shaw of the US Fish and Wildlife Service says researchers believe the eagles, which are scavengers, ingest the lead when they feed off leftover deer carcasses.

"Gut piles from deer shot with lead ammunition can be a potential source for lead exposure for scavenging animals like bald eagles," Shaw said. "More than a third of those eagles had liver-lead concentrations consistent with lead poisoning."

Deputy Refuge Manager Tim Yager says there are many things hunters can do to reduce lead intake for wild birds. 

"First would be to voluntarily utilize alternative forms of ammunition," Yager said. "Remove the gut piles, take them out of the field when you do kill an animal. Don’t just dress the animal, but take the whole carcass with you." 

Iowa requires hunters to use non-toxic ammunition for most birds. But for deer hunters, lead shot tends to be less expensive. A quick survey of Iowa sporting goods stores showed lead deer slug prices between $3.50 and $6.99 for five rounds. The non-lead equivalent, called Sabot, ranges from $8.99 to $18.99.