Jeff Cooper had a hunch. Toxins in the environment, and especially lead, he suspected, were hurting bald eagles in Virginia more than ecologists realized.
The findings went beyond Cooper’s fears: Nearly half of bald and golden eagles in the United States, and in the D.C. region, have chronic lead poisoning.
“I had an inclination,” Cooper said, “but I didn’t realize it was this widespread.”
The study was the product of a joint effort by Cooper’s Virginia agency, the U.S. Geological Survey, U.S. Fish and Wildlife, West Virginia University and Conservation Science Global, a nonprofit group based in Cape May, N.J. Over an eight-year period, researchers examined samples of bones, feathers and livers from more than 1,200 golden and bald eagles from 38 states, and tested blood from about 620 live birds.
Nearly half the eagles had what researchers called “unexpectedly high frequencies of lead,” experts wrote in the study, published earlier this year in the journal Science.
“The patterns are the same locally and nationwide, that bald and golden eagles showed signs of repeated lead exposure throughout their lives,” said Todd Katzner, principal investigator of the study and a USGS wildlife biologist. The study, he said, showed “the previously unseen challenges facing these birds of prey.”
Golden eagles and bald eagles, the national bird, have made a comeback, and experts estimate there are now approximately 350,000 total in the Lower 48. But the study’s findings raised concerns, wildlife experts said, that repeated lead poisoning could curtail the growth of eagle populations.
Lead, a highly toxic metal, is considered extremely dangerous to animals and people. Eagles and other scavengers ingest it when they feed on the remains of animals that have been killed with lead ammunition. They can also be exposed through mining, power plant emissions, aviation fuel, industrial paints and improperly discarded lead acid batteries.
“The skeleton of an animal is the long-term storage facility for lead,” Katzner said. “As lead enters their bodies, it is digested and broken down and then enters the circulatory system, and it can then affect soft tissue.
“It can raise the concentration of lead in their blood and organs for weeks,” he said. “Eventually, lead settles in their bones … where it can be stored for a lifetime or recirculated into the animal’s blood.”
The older a bird was, the higher the lead concentration in its bones, researchers found. They also discovered that the eagles suffered more short-term exposure in winter months, when live prey is harder to find and the birds more likely to “use dead animals as a food source.”
Birds can die after ingesting too much lead, and small exposures over time can “build up and create bone density issues, neurological problems and affect their nervous system and create respiratory issues,” Katzner said.
Vince Slabe, the lead author of the study and research wildlife biologist at Conservation Science Global, said lead weakens birds and can leave them unable to fly.
“The body thinks it’s an essential nutrient and tries to absorb it, but the toxin, even at the lowest levels, goes into their circulatory system,” he said.
The study found that golden and bald eagles in D.C., Maryland and Virginia had lead concentrations in their blood and livers that measured “above the threshold for clinical lead poisoning.” Roughly 46 percent of eagles from the region had lead in their femurs that was also high, suggesting they’d had chronic lead poisoning, or what scientists call “a lifetime of exposure.”
In Virginia, Cooper said, the research found that eagles had “very little — if any — lead before they had fledged.” Exposure began after they started to scavenge.
At the Wildlife Center of Virginia, a hospital in Waynesboro that researches and teaches about wildlife, experts said they’ve seen an uptick in the number of eagles they take in that have toxic lead levels. On average, about two-thirds of the eagles the center has taken in annually since 2016 have had positive lead-toxicity levels, according to Alex Wehrung, a spokesman for the group.
Improved technologies, surveillance and awareness are helping detect more such cases, he said.
“As populations grow, the suitable habitat for eagles near rivers is becoming more rare, so they’re moving inland, and their diet is changing from being a majority of fish to a diet of scavenging and eating carcasses,” Wehrung said. “As a result, we’re seeing more cases of positive lead toxicity in their blood. A lead fragment even the size of a grain of rice is enough to kill an otherwise healthy bald eagle.”
Widespread conservation efforts — including bans on pesticides, the passage of the Endangered Species Act in the 1970s, and protections for habitats, air and water — have helped eagle populations come back after the birds’ near-demise in the 1960s. In 2007, bald eagles were removed from the endangered species list.
But eagle populations are not “growing as fast as they could be if they weren’t experiencing lead poisoning,” said Slabe, the study’s lead author. Over a 20-year period, he said, “it becomes thousands of birds that are being removed from this population due to lead poisoning.”