Lead poisoning affects nearly half of the United States’ bald eagles, according to a recent study. In the first large-scale study of its kind, over 1,200 eagles were surveyed in 38 states. Researchers found that 46% of bald eagles and 47% of golden eagles had chronic lead poisoning.
The study was conducted by researchers at Conservation Science Global, a global nonprofit organization, in collaboration with other fellows. Led by Vincent Slabe, a wildlife biologist at Conservation Science Global, research occurred over eight years. During this period, researchers collected samples from several golden and bald eagles and analyzed them for lead contamination.
Researchers also found signs of immediate lead exposure in 27-33% of bald eagles and up to 35% of golden eagles. According to a Science article, “Models comparing natural and lead-caused deaths revealed lead levels would stunt annual population growth by 3.8% in bald eagles and 0.8% in golden eagles each year.”
The findings come amid the bald eagle population’s burgeoning recovery. In the 1960s, bald eagles faced possible extinction thanks to dichlorodiphenyltrichloroethane (DDT) pollution. The dangerous pesticide would wash into waterways and poison the birds, killing their hatchlings. After DDT was banned in the early 70s and the Endangered Species Act was put in place, the bald eagle population started growing again. Today, there are more than 300,000 bald eagles alive in the U.S., according to the Forest and Wildlife Service.
Bryan Watts, an ecologist at the College of William & Mary, says that the findings provide an opportunity to focus on eagles’ wellbeing. “It’s a strong paper that pulls together quite a bit of information,” Watts said. “This really solid analysis allows us to look at the eagles’ entire range.” Watts was not involved with the study.
Most eagles ingest lead that leaks from ammunition left in the bodies of deer and other animals hunted by humans. When the bird eats lead, it shows up in the bloodstream, passes through the liver and may accumulate in the bones. Over the years, wildlife clinics have reported instances of eagles with bullet fragments in their stomachs. Studies show that lead poisoning is a widespread problem for eagles. Ending or limiting sport hunting could help mitigate this issue.
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