WASHINGTON (AP) — America’s national bird is more under siege than previously thought, with nearly half of bald eagles tested in the United States showing signs of chronic lead exposure, according to a published study. Thursday.
As the bald eagle population has rebounded from the brink of extinction since the United States banned the pesticide DDT in 1972, harmful levels of toxic lead have been found in the bones of 46% of bald eagles. whiteheads sampled in 38 states from California to Florida, researchers reported in the journal Science.
Similar rates of lead exposure have been found in golden eagles, which the scientists say means the raptors likely consumed lead-contaminated carrion or prey from ammunition or fishing gear.
Blood, bone, feathers and liver tissue from 1,210 eagles sampled from 2010 to 2018 were examined to assess chronic and acute lead exposure.
“This is the first time for a wildlife species that we have been able to assess lead exposure and population-level consequences on a continental scale,” said study co-author Todd Katzner. wildlife biologist at the US Geological Survey in Boise, Idaho. “It’s kind of staggering that nearly 50% of them are 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. In high doses, lead causes seizures, breathing difficulties and death.
The study estimated that lead exposure reduced the annual population growth of bald eagles by 4% and golden eagles by 1%.
Bald eagles are one of America’s most famous conservation successes, and the birds were removed from the United States’ endangered species list in 2007.
But scientists say high lead levels are still a concern. In addition to suppressing eagle population growth, exposure to lead reduces their resilience to future challenges, such as climate change or infectious disease.
“When we talk about recovery, it’s not really the end of the story – there are always threats to bald eagles,” said Krysten Schuler, wildlife disease ecologist at the College of Veterinary Medicine. from Cornell University, which was not involved in the study.
Previous studies have shown high lead exposure in specific regions, but not across the country. Blood samples from live eagles in the new study were taken from trapped birds and studied for other reasons; the bone, feather, and liver samples were from eagles killed by collisions with vehicles or power lines, or other misfortunes.
“Lead is present in the landscape and available to these birds more than we previously thought,” said co-author Vince Slabe, a wildlife biology researcher at the nonprofit Conservation Science Global. “A lead fragment the size of the end of a pin is large enough to cause the death of an eagle. ”
The researchers also found high levels of lead exposure in the fall and winter, coinciding with hunting season in many states.
During these months, the eagles feed on carcasses and piles of guts left behind by hunters, which are often riddled with shards of lead shot or bullet fragments.
Slabe said the search result was not to disparage hunters. “Hunters are one of the best conservation groups in this country,” he said, noting that fees and taxes hunters pay help fund national wildlife agencies and that he also hunts. deer and elk in Montana.
However, Slabe said he hopes the findings will provide an opportunity to “speak clearly to hunters about this issue” and that more hunters will voluntarily switch to lead-free ammunition such as copper bullets.
Lead ammunition for waterfowl hunting was banned in 1991, due to concerns about contamination of waterways, and wildlife authorities encouraged the use of non-toxic steel shot. However, lead ammunition is still common for mountain bird hunting and big game hunting.
The amount of lead exposure varies by region, with the highest levels found in the central flyway, according to the new study.
At the University of Minnesota Raptor Center, veterinarian and executive director Victoria Hall said “85 to 90 percent of eagles that come to our hospital have some level of lead in their blood,” and X-rays often show lead bullet fragments in their stomachs.
Eagles with relatively low levels can be treated, she said, but those with high exposure cannot be saved.
Laura Hale, board chair of the nonprofit Badger Run Wildlife Rehab in Klamath County, Oregon, said she will never forget the first eagle she encountered with acute lead poisoning, in 2018. She had responded to a call from a resident about an eagle that appeared motionless in the undergrowth. and brought it to the clinic.
The young bald eagle was wrapped in a blanket, unable to breathe properly, let alone stand or fly.
“There’s something hideous about watching an eagle struggling to breathe from lead poisoning – it’s really, really hard,” she said, her voice shaking. This eagle had convulsions and died within 48 hours.
Lead in the landscape not only affects eagles, but many other birds as well — including hawks, vultures, crows, swans and geese, said Jennifer Cedarleaf, avian director at the Alaska Raptor Center, a research organization. nonprofit wildlife rescue in Sitka, Alaska.
Because eagles are so 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. “It’s the species that tell us: we have a little problem.”