Bald eagle populations have steadily increased in recent decades, after the use of DDT was banned in 1972. However, according to a new study led by Cornell University, this rebound is currently weakened by the threat of lead poisoning from gunshot ammunition.
Despite increasing numbers of bald eagles, lead poisoning from eating dead carcasses or parts contaminated by lead ammunition has reduced eagle population growth by 4 to 6 percent annually in the Northeast United States.
“Even though the population seems like it’s recovered, some perturbation could come along that could cause eagles to decline again,” said study senior author Krysten Schuler, an assistant professor in the Department of Public and Ecosystem Health at Cornell University.
Besides being potentially threatened by habitat loss, climate change, or the West Nile virus and other viral or bacterial outbreaks, bald eagles are increasingly affected by current hunting practices. Many hunters “field dress” game they shot with lead ammunition, leaving contaminated organs where the animal was killed. Bald eagles are scavenging such carcasses, often consuming bullet fragments that later on cause lead poisoning.
Although bald eagle numbers nearly quadrupled in the lower 48 states between 2009 and 2021, reaching about 316,000, the current findings on the dangers of lead poisoning raise alarms among scientists and conservationists.
“Hopefully, this report will add information that compels hunters, as conservationists, to think about their ammunition choices,” said Professor Schuler. In her view, a better alternative would be the use of copper-based ammunition.
Bald eagles are not the only species endangered by these hunting practices. Trail cameras have repeatedly shown that owls, crows, bears, foxes, coyotes, or fishers also scavenge the remains left by hunters.
“We haven’t collected data on these other species in the same way that we pay attention to eagles,” said Professor Schuler. “We’re putting eagles out there as a poster species for this issue, but they’re not the only ones being impacted.”
The study is published in the Journal of Wildlife Management.