‘Widespread’ lead poisoning discovered among U.S. eagle populations

RESTON, Va. — The bald eagle is synonymous with the United States. Unfortunately, a new troubling report from the U.S. Geological Survey has discovered evidence of “widespread” lead poisoning among both bald and golden eagle populations across America.

This first-of-its-kind long-term research project entailed tracking and evaluating lead exposure in bald and golden eagles between 2010 and 2018. Ultimately, study authors conclude there is little doubt that such extensive lead exposure has inflicted a serious toll on U.S. eagle populations.

“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,” says Anne Kinsinger, USGS Associate Director for Ecosystems, in a media release.

On a more detailed level, the research team assessed a total of 1,210 eagles living in 38 U.S. states (including Alaska). That analysis revealed lead poisoning among bald and golden American eagles is causing a notable decline in population growth rates; 3.8 percent annually for bald eagles and 0.8 percent annually among golden eagles.

“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,” explains lead USGS study author Todd Katzner, a USGS wildlife biologist.

Copper and lead ammunition comparison
Non-lead ammunition, such as those made from copper, tend to remain intact after impact with their target, while lead ammunition can fragment into many small pieces. (Photo by Mike McTee)

The eagle’s food supply is a major source of contamination

Stunningly, just under half of all examined eagles showed signs of repeated lead exposure, with signs of short-term exposure being more common during colder months. Both bald and golden eagles are natural scavengers, meaning they instinctively search out dead and decaying animals as sources of food. However, eagles are particularly prone to scavenging during winter months because other food sources are in short supply.

The most common way eagles are exposed to lead is by inadvertently consuming lead ammunition fragments within the carcasses of animals left behind by hunters, or by eating lead within gut piles left over from when game is dressed in the field.

Generally, older eagles showed higher levels of lead poisoning. This makes sense because lead never really leaves the body, it slowly accumulates in bone more and more over time.

“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,” concludes study co-author Brian Millsap, U.S. Fish and Wildlife Service National Raptor Coordinator.

The study is published in the journal Science.