In 1978, the bald eagle was listed for protection under the Endangered Species Act. Since then, the American bird has made an incredible comeback as Americans complied with hunting regulations and banned DDT, the infamous pesticide that decimated bird populations. Unfortunately, new research shows the emblematic species is facing another threat.

What’s new — A new study published in the journal Science examined data on more than 1,200 bald and golden eagles from 2010 to 2018 across 38 states and found that lead poisoning is suppressing population growth as these two raptors continue to make their comeback.

According to the report, lead poisoning drove a 4 percent suppression rate among bald eagles and a 1 percent suppression rate among golden eagles. A surprisingly high proportion of birds displayed chronic and acute health issues.

Much of the lead poisoning is attributed to shrapnel in hunted animals; when eagles feed on these dead animals, they ingest the lead.

While eagles are predators that pursue live animals, they’re known to eat carcasses, especially in winter when live food may be more scarce. Many hunters use lead ammunition, so bullets are embedded within the carcass’s flesh, as far as 18 inches from the entry hole.

“If you think about the very end of a pin, that little amount has the potential to cause mortality in an eagle,” Vince Slabe, a wildlife biologist for Conservation Science Global and a co-author on the study, tells Inverse.

They say there are other possible causes for lead poisoning, but they likely don’t account for the unexpected numbers. Eagles, they say, have been known to eat garbage in times of desperation, and they sometimes consume lead from tackle left in fish.

Why it matters — While population suppression in these bird species warrants concern, the bigger problem comes from its source. The fact that lead ammunition seems to be driving these poisonings means that it’s countering conservation. As Slabe explains, hunting at its best aids conservation; the two go hand in hand.

Slabe cites the Pittman-Roberson Act of 1937, also known as the Federal Aid in Wildlife Restoration Act, as a law that makes the hunting community a bulwark of conservation. “When [hunters] buy ammunition, hunting licenses, and guns, there’s a specific percentage that’s taxed, and that then goes into a federal pot of money that reached over a billion dollars last year,” he says. “That money is then divided amongst the states for conservation programs, acquiring wetlands and other habitat areas for wildlife, and to pay the salaries of wildlife biologists.”

What’s next — The problem’s cause may also be its solution. Slabe emphasizes the hunting community’s role in conservation. A 2009 paper examined hunters’ willingness to use other types of ammunition to reduce the amount of lead, finding that voluntary swaps are self-sustaining, so this is a seemingly doable fix.

Slabe says that solid alternatives are copper, steel, and bismuth, which don’t embed shrapnel and metal particles through the flesh. A copper bullet has “basically no fragments,” Todd Katzner, a wildlife biologist for the U.S. geological survey and a co-author on the study, tells Inverse.

Currently, the bird’s conservation status is of “least concern,” signaling that conservation efforts have paid off. But if nothing’s done, Slabe says, the stable population of these birds might not be so stable anymore.