DULUTH — New research shows that lead poisoning is impacting eagles across the North American continent, the first evidence that lead is having a population-level impact on the big birds of prey.
Scientists from Conservation Science Global, Inc., the U.S. Geological Survey, West Virginia University, the U.S. Fish & Wildlife and other institutions found that nearly half of the bald and golden eagles they studied showed chronic lead poisoning, and that lead poisoning is an important barrier to the growth of eagle populations across North America.
This paper, “Demographic implications of lead poisoning for eagles across North America,” is the first to show continentwide consequences of lead poisoning on any species of wildlife.
Lead is a highly toxic heavy metal ingested by eagles and other scavenging wildlife when they feed on the remains of animals that have been shot with lead ammunition, often deer carcasses or gut piles of animals that were shot with lead bullets, or birds that have been shot with lead shotgun pellets.
U.S. Fish and Wildlife Service researchers documented in 2012 that lead exposure is a significant mortality factor in bald eagles that inhabit the Upper Midwest Region. But the recent study appears to show a broader problem.
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“This is the first study of lead poisoning of wildlife at a nationwide scale, and it demonstrates the unseen challenges facing these two iconic eagle species,” Vince Slabe, lead author on the study and Research Wildlife Biologist for Conservation Science Global, said in a statement. “Medical science tells us that, for humans, there is no safe amount of lead. Today, we also know that redistributed lead in our environment is harming eagle populations across North America.”
This study evaluated lead levels in more than 1,200 bald and golden eagles sampled between 2010 and 2018 and found age-related and seasonal variation in lead poisoning.
“A few studies have shown these trends at a local level,” Todd Katzner, co-author and Research Wildlife Biologist for the U.S. Geological Survey, said in a statement. “But demonstrating these patterns at a continental scale helps us to understand what causes this variation and, potentially, how to address the issue.”
Minnesota lawmakers earlier this month heard testimony from wildlife biologists and wildlife veterinarians that lead ammunition should be banned for hunting in the state, especially considering nontoxic alternatives to lead are widely available and reasonably priced, such as shotgun shells filled with steel pellets or rifle ammunition using copper bullets.
"A single piece of lead the size of a grain of rice will kill a bald eagle," Victoria Hall, executive director of the University of Minnesota's Raptor Center, told lawmakers. Hall said more than 85% of eagles admitted to the center for any problem have unhealthy lead levels in their blood and that as many as 30% die due to fatal lead levels.
Lead shot has been banned for all waterfowl hunting in the U.S. for decades. It’s also been banned in gasoline and paint since the 1970s due to the extreme detrimental impacts of lead poisoning in people, especially children.
Bills have been introduced at the Minnesota Legislature to ban or restrict lead ammunition but so far have been defeated by efforts of the National Rifle Association and the gun industry group the National Shooting Sports Foundation, which say lead from ammunition is not a major animal or human health issue. They also said hunters would be faced with severe supply-side ammunition shortages if lead is banned or phased out for hunting.
Opponents to a lead ban also note that, while lead ammunition may kill a few individual eagles, the continental eagle population is at its highest in nearly 100 years, thanks in large part to the banning of the toxic pesticide DDT.
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But Chris Parish, president of The Peregrine Fund and co-founder of the North American Non-lead Partnership, said hunters should return to their conservation roots and go lead-free.
“With an ever-growing body of scientific findings, we hunters have an ever-improving understanding of the details of preventable exposure. The hunting community has a long-standing tradition of conservation of wildlife in the United States, and we are the key to solving the problem," Parish said in a statement.
