A unique eight-year study has found common and frequent lead poisoning in bald and golden eagles. According to the research, frequent lead poisoning has a negative effect on eagle populations by slowing reproduction rates.
The study was carried out by researchers at the US Geological Survey (USGS), Conservation Science Global Inc., and the US Fish & Wildlife Service.
“Studies have shown lethal effects to individual birds, but this new study is the first to show population-level consequences from lead poisoning to these majestic species at such a wide scale,” said Anne Kinsinger, USGS Associate Director for Ecosystems.
To carry out the study, the scientists used samples from 1,210 eagles across 38 states, including Alaska. The results show that lead poisoning has slowed the reproduction rate of bald eagles by 3.8 percent and golden eagles by 0.1 percent each year. This is the first study to look at lead poisoning across such a broad scale.
“This is the first study of lead poisoning of wildlife at a nationwide scale, and it demonstrates the unseen challenges facing these birds of prey. We now know more about how lead in our environment is negatively impacting North America’s eagles,” said Todd Katzner, USGS wildlife biologist and lead USGS author.
Nearly half the birds in the study showed evidence of repeated exposure to lead. The experts report that frequency of lead poisoning was influenced by age and, for bald eagles, by region and season.
In birds, lead poisoning is often caused by bullet fragments found in carcass remains or “gut piles” left by hunters. It’s for reasons like this that there was a now repealed ban on lead ammunition in wildlife refuges.
“The study’s modeling shows that lead reduces the rate of population growth for both of these protected species,” said Brian Millsap, U.S. Fish and Wildlife Service National Raptor Coordinator.
“That is not as impactful for bald eagles since this endemic species population is growing at 10 percent per year across the U.S. In contrast, the golden eagle’s population is not as stable, and any additional mortality could tip it towards a decline.”
The study is published in the journal Science.