Officials who are monitoring incidents affecting the eagle population in the United States are revealing a lingering danger that could cause a decline in the birds’ presence.

Todd Katzner, a US Geological Survey (USGS) wildlife biologist based in Boise, Idaho, told Fox News Digital via email that lead exposure of raptors, involving eagles and vultures, is a global phenomenon.

He said this has been seen on every continent as people hunt animals and leave bullets behind, as well as avian scavengers — birds that eat dead animals, which may then have remnants of ammunition embedded in their bodies.

Researchers found that of 448 birds from around the US, 50% of the winged animals had evidence of chronic lead poisoning, according to a recent USGS and collaborator’s paper published at Science.org.

“In this case, ‘chronic’ means ‘repeated exposure,’ meaning 50% of the eagles were getting exposed to lead again and again,” Katzner said. 

“Most of the others had evidence of lead exposure, just not as frequent as the 50% that showed chronic exposure,” he also said. 

In Feb. 2023, officials in Lancaster County, Pennsylvania, experienced an incident when a bald eagle — America’s bird — died from lead poisoning.

“An eagle is supposed to be the strong, powerful symbol of America, and here he lies lifeless as [he] lost the fight to lead poisoning,” officials with the Raven Ridge Wildlife Center in Washington Boro, Pennsylvania, posted on Facebook in 2023 — adding a plea to sportsmen to make “the switch to go lead free” in hunting practices.

Three months ago, Lancaster County found another eagle dead as a result of lead poisoning.

This past January in Indiana, a bald eagle was transferred to Humane Indiana Wildlife Rehabilitation and Education Center after the bird was found suffering from lead poisoning at Potato Creek State Park.

“Our team provided stabilizing care, administering fluids, a critical care food alternative, and began chelation therapy. With lead levels as high as they were, and with as poor [a] body condition as he was in, we were not terribly surprised to find that he had sadly passed away overnight,” Humane Indiana Wildlife officials wrote on Facebook.

“A lead fragment the size of a grain of rice is lethal to a mature bald eagle, meaning that a standard 150 grain lead bullet can poison 10 eagles,” the post went on. 

“The deadly metal accumulates in an eagle’s system over the course of [its] life, meaning that there is no safe amount of lead exposure. For this reason, lead is often called ‘the silent killer,'” the post also noted.

Katzner said that although “hunting provides an important food source for these birds … they are also potentially a source of lead.”

He said bird scavengers get lead poisoning from finding game or remnants of game shot by hunters.

“When a lead bullet hits an animal, it fragments into tens or hundreds, sometimes thousands, of fragments. If the hunter recovers their [target], then often they leave a gut pile that contains lead fragments,” Katzner said. 

“If the hunter does not recover their target, then the animal’s carcass will contain those lead fragments.”

He added that birds will often eat those carcasses or remains — making them highly susceptible to lead poisoning.

Fish comprise about 70% to 90% of an eagle’s diet, yet the bird “will feed on what is most available, and requiring the least amount of energy to acquire it,” according to the American Bald Eagle Foundation.

Katzner said there is good evidence that using non-lead ammunition can help decrease the rates of lead poisoning.

In addition to the consumption of lead ammunition, lead poisoning can also come from the diet.

“Lead poisoning rates can also be high for other birds such as a red-shouldered hawk that eats earthworms, which tend to concentrate [the] lead in their bodies,” Katzner said.