The findings went beyond Cooper’s fears: nearly half of bald eagles and golden eagles in the United States and the DC area suffer from chronic lead poisoning.
“I had an inclination,” Cooper said, “but I had no idea it was so prevalent.”
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The study is a joint effort of Cooper’s Virginia, the US Geological Survey, US Fish and Wildlife, West Virginia University, and Conservation Science Global, a nonprofit group based in Cape May, NJ. Over an eight-year period, researchers examined bone, feather and liver samples from more than 1,200 golden and bald eagles from 38 states, and blood tests from about 620 live birds.
Nearly half of the eagles had what the researchers called “surprisingly high lead frequencies,” experts wrote in the study, published earlier this year in the journal Science.
“The patterns are the same locally and across the country, as bald and golden eagles showed signs of repeated lead exposure throughout their lives,” said study lead researcher Todd Katzner. and wildlife biologist at the USGS. The study, he said, showed “the unprecedented challenges facing these birds of prey”.
Golden eagles and bald eagles, the national bird, have made a comeback, and experts estimate there are now around 350,000 total in the lower 48. But the study’s findings raised concerns, wildlife experts said, that repeated lead poisoning could stunt the growth of eagle populations.
Lead, a highly toxic metal, is considered extremely dangerous to animals and humans. Eagles and other scavengers ingest it when feeding on the remains of animals killed with lead ammunition. They can also be exposed through mining, power plant emissions, aviation fuel, industrial paints, and improperly discarded lead-acid batteries.
“An animal’s skeleton is the long-term storage facility for lead,” Katzner said. “When lead enters their body, it gets digested and broken down, then enters the circulatory system, and then it can affect soft tissue.
“It can increase the lead concentration in their blood and organs for weeks,” he said. “Eventually the lead is deposited in their bones… where it can be stored for a lifetime or recirculated back into animals some blood.”
The older a bird is, the higher the concentration of lead in its bones, the researchers found. They also found that eagles suffered from shorter-term exposure during winter months, when live prey is harder to come by and birds are more likely “to use dead animals as a food source. “.
Birds can die from ingesting too much lead, and small exposures over time can “build up and create bone density issues, neurological issues and affect their nervous system and create respiratory issues,” Katzner said. .
Vince Slabe, the study’s lead author and wildlife biologist research at Conservation Science Global, said lead weakens birds and can prevent them from flying.
“The body thinks it’s an essential nutrient and tries to absorb it, but the toxin, even at the lowest levels, enters their circulatory system,” he said.
The study found that golden and bald eagles in DC, Maryland and Virginia had blood and liver lead concentrations measured “above the threshold for clinical lead poisoning”. About 46% of the eagles in the area had lead in their femurs which was also high, suggesting they had had chronic lead poisoning, or what scientists call “lifetime exposure”.
In Virginia, Cooper said, research found eagles had “very little — if any — lead before they flew off.” The exposure started after they started feeding.
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At the Wildlife Center of Virginia, a hospital in Waynesboro that researches and teaches about wildlife, experts said they’ve seen an increase in the number of eagles they take in that have toxic lead levels. On average, about two-thirds of the eagles the center welcomes each year since 2016 have positive lead toxicity levels, according to Alex Wehrung, a spokesman for the group.
Improved technologies, surveillance and awareness are helping to detect more such cases, he said.
“As populations increase, suitable habitat for eagles near rivers becomes increasingly scarce, so they move inland and their diet shifts from a majority of fish to a diet of scavengers and carcasses,” Wehrung said. “As a result, we are seeing more cases of positive lead toxicity in their blood. A lead fragment the size of a grain of rice is enough to kill an otherwise healthy bald eagle.
Widespread conservation efforts – including the banning of pesticides, the passage of the Endangered Species Act in the 1970s, and the protection of habitats, air and water – have helped the eagle populations to return after the birds nearly disappeared in the 1960s. In 2007, the bald eagle was removed from the endangered species list.
But eagle populations aren’t “growing as fast as they could be if they weren’t suffering from lead poisoning,” said Slabe, the study’s lead author. Over a 20-year period, he said, “thousands of birds are removed from this population due to lead poisoning.”