The bald eagle population has been slowly recovering from the impact of a pesticide that nearly drove them to extinction decades ago. But now researchers at Cornell University have discovered that lead ammunition continues to hamper the resilience of these American icons.
The use of lead ammunition in bald eagle habitats reduced population growth by 4% to 6% per year in the Northeast, even as their populations soared in the lower 48 states in 2009 to 2021, according to a study published in the Wildlife Management Journal.
Eagles feed on carcasses left behind by hunters and dead animals can be contaminated with lead ammunition. The research covers decades of data, between 1990 and 2018, and covers seven states: Connecticut, Massachusetts, Maine, New Hampshire, New Jersey, New York and Vermont.
And while this study focuses on bald eagles, it could have implications for the welfare of other animals that are also known to feed on carcasses, including crows, coyotes and foxes.
“What we have is a lot of data on bald eagles,” said Dr. Krysten Schuler, wildlife disease ecologist and co-director of the Cornell Wildlife Health Lab. “Those are sort of the poster species that we use for this problem because we don’t have the same amount of data to do this kind of analysis on other species.”
The bald eagles – hailed as an “American success story” by the US Fish and Wildlife Service – were threatened by the use of DDT, a pesticide that nearly wiped out their population. The pesticide was banned in 1972 and the eagles were included on the endangered species list in the Endangered Species Act 1973. In 2007, bald eagles were removed from the list.
Lead ammunition didn’t stop the eagles’ recovery, but it didn’t help either, Schuler explained.
When a hunter shoots a deer with lead ammunition, the bullet scatters into small pieces. If a hunter “field dresses” the carcass by removing its internal organs, the organs left behind carry lead fragments, Schuler told NPR. Eagles unknowingly feed on lead-contaminated organs.
Lead is toxic to everyone, but the acid in eagles’ stomachs breaks down the lead, eventually causing it to circulate through their bodies, Schuler said.
“It’s an anthropomorphic source of mortality,” Schuler said. “Eagles pick up lead from the environment that we put in there, and, you know, with hunting ammunition, hunters have a choice of what they use.”
Using other types of ammunition, such as copper, could help keep lead out of bald eagle habitats. Burying the organs of a carcass shot with lead ammunition could also prevent the contaminant from impacting the eagle population, Schuler said.
“It’s definitely not an anti-hunting effort,” Schuler said. “We really try to emphasize choice and the components of education.”
Discussion of the use of lead ammunition has also reached Washington.
On the last day of President Barack Obama’s administration, the outgoing Director of Fish and Wildlife banned lead ammunition from national wildlife refuges. A few weeks later, President Donald Trump’s first interior secretary overthrew him.
In July 2020, Rep. Ted Lieu, D-California, introduced a bill that would ban lead ammunition on U.S. Fish and Wildlife Services land. The bill died in Congress. At the state level, a member of the Maine Legislative Assembly, Representative Amy Roeder, introduced a similar bill in March 2021. The bill also died.
“Lead is a deadly toxin,” Lieu told Boise State Public Radio in 2020. “We shouldn’t just be spreading it all over the place with ammunition and it’s also deadly to animals.”
With the publication of the study, the researchers publicly shared their software so others could use it to investigate other species.
“When we started, we didn’t know what we were going to find,” Schuler said. “But it’s been a big question, you know, for as long as I can think of in my career.”