A first-of-its-kind, eight-year study has found widespread and frequent lead poisoning in North American bald and golden eagles impacting both species’ populations. The paper, “Demographic Implications of Lead Poisoning for Eagles Across North America,” was published in the journal Science. Led by scientists from the U.S. Geological Survey, Conservation Science Global, Inc., and U.S. Fish and Wildlife Service, researchers evaluated lead exposure in bald and golden eagles from 2010 to 2018.
“Studies have shown lethal effects to individual birds, but this new study is the first to show population-level consequences from lead poisoning to these majestic species at such a wide scale,” said Anne Kinsinger, USGS Associate Director for Ecosystems.
These findings are the first to look at bald and golden eagle populations across North America, using samples from 1,210 eagles over 38 U.S. states including Alaska. Poisoning at the levels found in the study is causing population growth rates to slow for bald eagles by 3.8 percent and golden eagles by 0.8 percent annually. Previously, evaluations of lead exposure and its impact on eagle populations were only performed in local and regional studies. This groundbreaking study documents how lead poisoning inhibits both species’ population growth across North America.
“This is the first study of lead poisoning of wildlife at a nationwide scale, and it demonstrates the unseen challenges facing these birds of prey. We now know more about how lead in our environment is negatively impacting North America’s eagles,” said Todd Katzner, USGS wildlife biologist and lead USGS author.
In this study, almost 50 percent of the birds sampled showed evidence of repeated exposure to lead. Short-term exposure was more frequent in winter months. Both eagle species are scavengers and use dead animals as a food source year-round, but particularly rely on them during the winter months when live prey is harder to find. Lead poisoning typically occurs when an eagle eats lead ammunition fragments lodged inside an animal carcass or in gut piles left behind when game is dressed in the field. The frequency of chronic lead poisoning found in both species increased with age because lead accumulates in bone as eagles are repeatedly exposed to the heavy metal throughout their lives.
“The study’s modeling shows that lead reduces the rate of population growth for both of these protected species. That is not as impactful for bald eagles since this endemic species population is growing at 10 percent per year across the U.S. In contrast, the golden eagle’s population is not as stable, and any additional mortality could tip it towards a decline,” said Brian Millsap, U.S. Fish and Wildlife Service National Raptor Coordinator and co-author.
This study included authors from academia, nonprofits, consulting services, industry, state, federal and international agencies. Funding was provided by nonprofit foundations and state and federal agencies.