Almost half of the bald and golden eagles in the United States showed signs of chronic lead poisoning, according to a study published on Thursday by the journal Science.
The bald eagle population has rebounded from near-extinction in the 1960s after the United States banned the pesticide DDT in 1972, and enacted the Endangered Species Act of 1973 that protected bald eagles.
Nearly 46% of bald eagles tested across 38 different states were found to have chronic lead poisoning.
Vincent Slabe, a wildlife biologist at the nonprofit Conservation Science Global, and his colleagues studied the blood, liver, and feather tissues in 1,210 bald and golden eagles over an eight-year period from 2010-2018.
"It’s a strong paper that pulls together quite a bit of information," Bryan Watts, an ecologist at the College of William & Mary who was not part of the study, said. "This really solid analysis allows us to look at the eagles' entire range."
There are reportedly more than 300,000 bald eagles living in the wild today.
"Bald eagle populations are doing brilliantly in the U.S.," Todd Katzner, a conservation ecologist with the U.S. Geological Survey and an author of the study, said.
Similar to the bald eagle, 47% of the golden eagle population was also suffering from chronic lead poisoning. Their population has been more affected, as there were just 40,000 golden eagles in 2016 in the United States.
"Their populations are much more on the edge," Katzner said.
Eagles often consume lead in the form of ammunition that is left behind in deer and other animals. The lead goes into the bloodstream, then is filtered through their livers, and can even build up in their bones depending on how much lead has been consumed.
The study's model compared natural and lead-caused deaths showed that it would stunt population growth in bald eagles by 3.8% and in golden eagles by 0.8%.
Both Slabe and Katzner believe that a yearly deduction, no matter the percentage, will add up over time and greatly affect the eagle population.
"It’s like compound interest," Katzner said.
Conservation groups have pushed for bans on lead ammunition over the recent years. California stopped its usage in 2019 to protect the California condor population. Authors of the study have tried to educate hunters on the dangers of lead poisoning and have even suggested the use of alternative ammunition, like copper bullets.
"The hunting community remains mostly unaware" of lead ammunition's impact on eagles, Slabe said. "But in the hunter education programs I’ve done, they’re really receptive to this issue."
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