An increasing number of bald eagles have been admitted to wildlife-rehabilitation centers across Pennsylvania exhibiting signs of illness such as weakness, lethargy, emaciation, labored respiration and drooping wings.

Blood tests often reveal that the eagles are suffering from lead toxicity.

Lead poisoning occurs when toxic levels of lead are absorbed into the body.

Raptors are particularly susceptible to lead poisoning because when they ingest lead particles, the acidic nature of their stomach causes rapid absorption of the metal, said Pennsylvania Game Commission wildlife veterinarian Justin Brown.

“Lead poisoning is a debilitating disease in bald eagles,” said Brown. “You have this powerful bird and you find it in the field — limp and weak. You can pick it up and it doesn’t even know you are there. “

After a blood test reveals that a bald eagle has lead toxicity, intensive treatments can begin. Drugs treatments can take the metal out of the body’s tissue and blood. And if metal is detected in an eagle’s digestive system, it can be flushed out and removed. But treatment often is unsuccessful because the eagles have already absorbed too much lead.

In the past year, Red Creek Wildlife Center has treated 12 bald eagles with lead toxicity and only one of those eagles survived, said center director Peggy Hentz.

“As there are more eagles in the wild, we are getting more eagles in the wildlife-rehabilitation centers and the problem has become evident,” Hentz said.

Since 2006, the Game Commission has been conducting necropsies on bald eagles that die to monitor causes of death and potential diseases. The data from 2006 to 2016 reveals that approximately one-third of the state’s known bald-eagle mortalities are associated with a toxin, with lead being the most common. In fact, lead toxicity is a significant cause of death in all raptors, not just eagles.

Lead is a heavy, relatively inexpensive, malleable metal, which often is used in fishing lures, ammunition and other materials. Research has shown that fragments of lead can be found as far as 18 inches from a bullet’s point of impact. In addition, 30 to 40 percent of the lead can remain in the target after the bullet has passed through. Small-game carcasses and big-game entrails that remain in the field could contain lead that might be ingested by opportunistic scavenging eagles and other wildlife.

The main source of ingested lead has not been clearly identified. However, hunters can help to reduce the potential that bald eagles ingest lead fragments from the remains of harvested game animals by burying the carcasses and gutpiles, or by covering them with branches. Doing so will make it less likely that aerial scavengers will find and consume the remains, which might contain lead particles. Hunters also could consider eliminating lead from their harvests by using non-lead ammunition.

Although lead toxicity has been identified as a leading cause of mortality among the state’s eagles, the eagle population continues to thrive and increase in number. In the early 1980s, there were only three active bald eagle nests in Pennsylvania. Today, thanks to the restoration efforts of the Pennsylvania Game Commission and partners, there are more than 250 active bald eagle nests in the state. Bald eagles met the requirements for removal from the state threatened species list in 2014 and are now classified as a protected species.