EVANSVILLE — As the population of the formerly endangered bald eagle has grown nationwide, a new threat to its survival is emerging.
Once threatened by agricultural pesticide use and hunting, bald eagles are now seeing an increase in deaths from lead poisoning.
"It's one of the most ironic parts of the conservation movement," said Laura Edmunds, clinical director at the Indiana Raptor Center in Nashville. "The only reason it hasn't had more attention until now is that there are more eagles now."
The effects of lead toxicity might have stayed undetected if conservationists hadn't been so successful at restoring eagles' numbers, she said.
How do bald eagles get lead poisoning?
The source? Wildlife experts believe it's lead ammunition used by hunters — bullet fragments and shotgun pellets left in wounded animals that then fall prey to or are scavenged by eagles.
An eagle is more likely to pick a wounded duck or other animal for its next meal than a healthy one that may not be as easy to catch, Edmunds said. In cold weather months, eagles might scavenge more as well.
Once a federal and state-endangered species, eagles thrived under protection. In 2007, they were removed from the federal endangered species list; Indiana pulled the eagle from its endangered list a year later.
Currently, there are an estimated 350 nesting pairs of eagles in Indiana, said Amy Kearns, assistant ornithologist at the Indiana Division of Fish & Wildlife.
Kentucky counted 187 occupied bald eagle nests as of 2019, the most recent year for which information is available, according to the Kentucky Department of Fish & Wildlife Resources.
More:Once nearly gone from Indiana, bald eagles have made a spectacular comeback in the state
While raptor rehabilitators have been encountering and dealing with the problem for awhile, a new study is shedding more light on how big the problem is.
The long-term study by U.S. Geological Survey scientists revealed widespread lead poisoning in bald eagles and golden eagles at levels high enough to reduce their populations.
"It definitely has the potential to threaten the eagle's recovery," Edmunds said.
She said the Raptor Center takes in varying numbers of injured eagles that also have lead poisoning each year.
"Some years we will get four or five but some years we may get one," Edmunds said.
What are the symptoms of lead poisoning in eagles?
Symptoms of lead poisoning in eagles and other raptors include droopy, lethargic behavior, poor take-off for flight and an inability to hold their head up, she said.
The Brown County, Indiana-based nonprofit organization is dedicated to rehabilitating birds of prey and returning them to the wild.
There are affordable ways to check for blood lead levels and treat it when possible, Edmunds said. Wildlife rehabilitators can use a chemical injection process called chelation therapy to unbind lead and other heavy metals from red blood cells and remove it from the body.
Edmunds said another source of lead might be from shot that has fallen to the body of ponds and water bodies. She believes diving water fowl such as Northern Shoveler ducks, which are common, inadvertently ingest it. The ducks in turn become prey for the eagles.
The Talon Trust, an Evansville-based raptor rescue nonprofit is not certified for long-term care of eagles but sometimes provides local, short-term care when an eagle is injured.
Lauren Norvell, its founder, recalled helping an eagle with lead poisoning that had been found on the ground, unable to fly. After about two months of treatment using chelation, it was returned to the wild.
"The lead can just really impact their neurological system," she said.