An increased number of bald eagles have been taken in to wildlife-rehabilitation centers for lead poisoning across Pennsylvania, with most cases proving to be fatal.

According to a release from the Pennsylvania Game Commission, from 2006 to 2016, “approximately one-third of the state’s known bald eagle mortalities (were) associated with a toxin, with lead being the most common.”

Susan Gallagher, chief naturalist from the Carbon County Environmental Education Center, confirmed that two bald eagle deaths in this area were connected to lead poisoning during the past year, with another two cases appearing to be linked to the same issue.

“We did not have success in those two confirmed cases, as the birds had been down for a while and had suffered a lot of damage,” Gallagher said.

Signs of lead poisoning in eagles can include weakness, lethargy, emaciation, labored respiration and drooping wings.

Gallagher said that these fatalities are above average, though proportionally, they could just be the result of an increased bald eagle population in the area.

In the past year, Red Creek Wildlife Center in Schuylkill Haven has treated 12 bald eagles with lead toxicity and only one of those eagles survived, the game commission said.

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

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.

According to the game commission, 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.

Bald eagles, much like other raptors, are especially susceptible to lead poisoning due to the acid in their stomachs, which causes rapid absorption of the metal. Often, the lead comes from tackle equipment like sinkers, or lead-based ammunition, that the eagle consumes along with fish or game.

Treatments for lead poisoning, such as calcium EDTA, can sometimes alleviate the condition by binding with the metal and flushing it out of the birds’ systems, but advanced cases are frequently fatal.

Gallagher said a fellow animal rehabilitator had a bird that responded well to treatment, but died shortly thereafter from what appeared to be a sort of traumatic heart condition, likely due to the damage from the lead.

The cause of death was not confirmed through autopsy, however, as all deceased eagles are sent off to the National Eagle Repository in Colorado, where the carcasses or parts are only available to Native American tribes for religious and cultural ceremonies.

Gallagher said prevention is easily the best method to put a stop to lead poisoning in eagles.

“We encourage sportsmen to use non-lead ammunition and non-lead tackle,” Gallagher said. “It may be difficult to find, but having seen those eagles die, if someone can prevent that kind of thing, they should do whatever they can to do so.”

The main source of ingested lead has not been clearly identified.

However, the game commission asks hunters to help to reduce the potential that bald eagles ingest lead fragments from the remains of harvested game animals by burying the carcasses and gut piles, 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, 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.