WASHINGTON—America’s national bird is more beleaguered than previously believed, with nearly half of bald eagles tested across the U.S. showing signs of chronic lead exposure, according to a study published Thursday.
Researchers reported that harmful levels of lead found in bones from 46% of the 38 states in which baldeagles were sampled, from California to Florida in order for them to recover from near extinction. Science.
Scientists have found similar levels of lead exposure in golden eagles. This suggests that the birds likely ate prey or carrion contaminated with lead by ammunition and fishing tackle.
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To assess acute and chronic lead exposure, the blood, bone, liver, and feathers of 1210 eagles were tested from 2010-2018.
“This is the first time for any wildlife species that we’ve been able to evaluate lead exposure and population level consequences at a continental scale,” said study co-author Todd Katzner, a wildlife biologist at U.S. Geological Survey in Boise, Idaho. “It’s sort of stunning that nearly 50% of them are getting repeatedly exposed to lead.”
Lead is a neurotoxin that even in low doses impairs an eagle’s balance and stamina, reducing its ability to fly, hunt and reproduce. Lead can lead cause seizures, breathing problems, and even death in high amounts.
According to the study, lead exposure had a significant impact on the population growth of golden and bald eagles.
Bald eagles are one of America’s most celebrated conservation success stories, and the birds were removed from the U.S. Endangered Species in 2007.
However, scientists warn that elevated levels of lead are still a problem. Lead exposure not only reduces eagle growth but also decreases their ability to face future challenges such as climate change and infectious diseases.
“When we talk about recovery, it’s not really the end of the story — there are still threats to bald eagles,” said Krysten Schuler, a wildlife disease ecologist at Cornell University’s College of Veterinary Medicine, who was not involved in the study.
Studies in the past have found high levels of lead exposure only in certain areas, not all over the country. In the current study, blood samples were collected from live eagles. The bone, feather, and liver samples were from birds that had been trapped.
“Lead is present on the landscape and available to these birds more than we previously thought,” said co-author Vince Slabe, a research wildlife biologist at the nonprofit Conservation Science Global. “A lead fragment the size of the end of a pin is large enough to cause mortality in an eagle. ”
Research also showed that lead exposure was elevated in winter and fall, which coincides with the hunting season in many States.
These months are when eagles hunt for carcasses or gut piles that have been left behind by hunters. They often contain shards of bullets and lead shot.
Slabe indicated that Slabe was not trying to discredit hunters. “Hunters are one of the best conservation groups in this country,” he said, noting that fees and taxes paid by hunters help fund state wildlife agencies, and that he also hunted deer and elk in Montana.
However, Slabe said he hopes the findings provide an opportunity to “talk to hunters about this issue in a clear manner” and that more hunters will voluntarily switch to non-lead ammunition such as copper bullets.
Waterfowl hunting with lead ammunition was stopped in 1991 due to contamination concerns. Officials encouraged wildlife officials to use nontoxic steelshot. Lead ammunition remains common in big game hunting as well as upland bird hunting.
New research has shown that lead exposure can vary by region. The highest levels are found in Central Flyway.
At the University of Minnesota’s Raptor Center, veterinarian and executive director Victoria Hall said that “85 to 90% of the eagles that come into our hospital have some level of lead in their blood,” and X-rays often show fragments of lead bullets in their stomachs.
Eagles with relatively low levels can be treated, she said, but those with high exposure can’t be saved.
Laura Hale, board president at nonprofit Badger Run Wildlife Rehab in Klamath County, Oregon, said she’ll never forget the first eagle she encountered with acute lead poisoning, in 2018. She had answered a resident’s call about an eagle that seemed immobile in underbrush and brought it to the clinic.
This blanket prevented the young baldeagle from being able to move or stand.
“There is something hideous when you watch an eagle struggling to breathe because of lead poisoning – it’s really, really harsh,” she said, her voice shaking. Within 48 hours, the eagle died from convulsions.
Lead on the landscape affects not only eagles, but also many other birds — including hawks, vultures, ravens, swans and geese, said Jennifer Cedarleaf, avian director at Alaska Raptor Center, a nonprofit wildlife rescue in Sitka, Alaska.
Because eagles are very sensitive to lead, are so well-studied and attract so much public interest, “bald eagles are like the canary in the coal mine,” she said. “They are the species that tells us: We have a bit of problem.”
