Story at a glance
- Researchers analyzed the tissue of 1,210 bald and golden eagles across 38 states over a period of eight years.
- They found that 46 percent of bald eagles died of lead poisoning.
- Scientific models predicted that lead-caused deaths can stunt bald eagles’ population growth by just under 4 percent annually.
Just as the American bad eagle population has soared in recent years, new research has found the population is facing a new setback: lead poisoning.
New research published in Science found that almost half of bald and golden eagles in the U.S. have lead poisoning, with eagles surveyed across 38 states over a period of eight years. Tissue from 1,210 bald and golden eagles were collected and the results showed chronic lead poisoning in 46 percent of bald and 47 percent of golden eagles.
Scientists also found signs of more immediate lead exposure in 27 percent to 33 percent of bald eagles and 7 to 35 percent of golden eagles, with the proportion dependent on the type of tissue collected.
Models comparing natural and lead-caused deaths also showed that lead levels can stunt the annual population growth of bald eagles by just under 4 percent, and just shy of 1 percent in golden eagles every year.
Though the lead poisoning is alarming to scientists, Bryan Watts, an ecologist at the College of William & Mary, told Science he isn’t sure that a 4 percent drop in population growth will put a meaningful dent in bald eagles’ recovery. He noted that many local populations include a “buffer” group of non-breeding adult eagles that could swoop in and reproduce if some are lost.
Currently, there are more than 300,000 bald eagles in the wild today, and Todd Katzner, a conservation ecologist with the U.S. Geological Survey and author of the new research, said, “bald eagle populations are doing brilliantly in the U.S.”
However, previous research published in the Journal of Wildlife Management warned that bald eagles are being threatened by spent lead ammunition left in carcasses of animals that eagles feed on. The study estimated lead contamination could reduce eagle population growth by 4 to 6 percent annually in the Northeast.
“Even though the population seems like it’s recovered, some perturbation could come along that could cause eagles to decline again,” said Krysten Schuler, a researcher from Cornell University and senior author of the study, in a statement.
That assessment appears to have come true as scientists studied the tissue of nearly 1,200 bald and golden eagles.
Wildlife rehabilitation clinics have long reported incidents of eagles with bullet fragments in their stomachs and studies sampling lead in local eagle populations have also hinted that poisoning could become a widespread problem.
Outside of death, if birds ingest large quantities of lead it can lead to harmful effects on the animals’ nervous and reproductive systems. Poisoned eagles may also experience loss of balance, tremors and impaired ability to fly.
There have been decades of federal protections for bald eagles as they once neared the edge of extinction, reaching an all-time low of just 417 known nesting pairs in the continental U.S. in the early 1960s.
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