Nearly one-third of the bald eagles in the United States are infected with a previously unknown virus, according to new research.
The study, which was published in the journal Scientific Reports on Friday, tested 47 eagles from 19 states and found that 32% of them had the newly identified virus, called bald eagle hepacivirus.
“This study has opened our eyes to glaring knowledge gaps about infection in a species of great national importance,” Tony Goldberg, lead study author and professor at the University of Wisconsin-Madison, said in a statement. “It’s a more complicated story than we thought it might be at first, but that makes it more interesting.”
While not deadly, the newly identified disease could be contributing to a separate, fatal disease that has been causing declines in the bird’s populations. Wisconsin River Eagle Syndrome was first described in the 1990s, when observers spotted birds staggering and vomiting. They eventually died from the syndrome or were euthanized.
It is unclear what the link between the two diseases could be, if there is one. Birds outside of Wisconsin that didn’t have the fatal syndrome were still diagnosed with the newly identified virus.
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“This study is another piece of the puzzle,” Sean Strom of the Wisconsin Department of Natural Resources said in a statement. “Hopefully we can find more pieces and figure out what is happening.”
Despite being the U.S.’s national symbol, bald eagles have had a rough history in the country. Hunting, pesticide poisoning and habitat loss decimated populations in the 20th century. As few as 412 nesting pairs were in the U.S. at the population’s lowest point.
Strict regulations and the banning of DDT, a pesticide that caused the bird’s egg shells to become too thin, recovered populations to the point that the bald eagle was taken off the endangered species list in 2007.
Despite improved protections, bald eagles are still falling victim to poison. In March, seven bald eagles and one great horned owl were found dead in Maryland. Officials said they were likely unintentionally poisoned with a banned pesticide, carbofuran. The deaths came roughly three years after 13 bald eagles were found dead in the area under similar circumstances. Officials said they were “disappointed and frustrated” at the continued poisonings.