A colony of bats near Libby Dam tested positive for the fungus that causes white-nose syndrome, marking the first detection of the deadly disease in western Montana.
Since it was first observed in New York in 2006, white-nose syndrome has killed millions of bats across the U.S. and Canada.
The disease is caused by a cold-loving fungus, which colonizes the skin of bats. As the fungus grows, it eats lesions into the bat’s wings and begins to disrupt physiological systems, including the bat’s hibernation cycles. Infected bats wake up frequently during the winter. The increased activity eventually leads to starvation as the bat depletes its fat reserves.
“This is probably one of, if not the most, detrimental wildlife disease we’ve seen in North America,” said Shannon Hilty, the state bat biologist for Montana Fish, Wildlife and Parks.
The disease is not only deadly, often killing 90-100% of bats in infected colonies, but also highly infectious, with detections now recorded in 45 U.S. states and 10 Canadian provinces. Biologists unearthed the first signs of the fungus in eastern Montana in 2020, but Hilty said she hadn’t expected the disease to crop up as far west as Lincoln County.
“I thought we had more time before it jumped the Continental Divide,” she said. “I think we all did.”
Every spring, state biologists swab bats at more than 30 roosting sites across the state, as part of ongoing efforts to monitor the spread of white-nose syndrome. This year was the first time a sample from western Montana returned a positive result.
The positive samples were collected from a group of about 1,500 Yuma myotis and little brown bats roosting in bat boxes near Libby Dam. While the fungus was detected, Hilty said none of the bats showed symptoms of white-nose syndrome when researchers collected the samples in May.
“That’s pretty typical,” she said. “There’s usually a lag between the detection of the fungus and detection of disease.”
Both species hibernate, making them susceptible to white-nose syndrome. A study published in Conservation Biology found that the number of little brown bats, in particular, had declined by 90% between 1995 and 2018 in areas where white-nose syndrome was present.
That sort of drop could have cataclysmic effects for communities in northwestern Montana. The 15 bat species native to Montana are all insectivores and provide the state with the equivalent of $680 million a year in agricultural pest control, according to Montana Fish, Wildlife and Parks.
But Hilty said there are reasons to be optimistic about the fate of the Libby colony. In many areas, bats hibernate in large colonies, which can facilitate the spread of fungi and other pathogens. Scientists believe bats in western Montana are more likely to tuck themselves into rocky crevasses or beneath the eaves of a house to hibernate alone.
Technological advancements are also providing wildlife managers with more options to contain the disease, including a promising new vaccine that is currently being tested in Glacier National Park. Last summer, a team of researchers administered the oral vaccine to 75 little brown bats captured near St. Mary. Another 75 bats received a placebo vaccine. The team will use tracking devices to monitor the bats over several years and track their long-term survival.
Researchers believe the vaccine is most effective when it is received before bats are exposed to white-nose syndrome, but trials in areas already infected by the fungus have also proven promising. In 2021, scientists immunized a colony of bats in Minnetonka Cave in Idaho after detecting the fungus. As of 2024, symptoms of white-nose syndrome had yet to emerge.
Hilty is hopeful a similar vaccination effort could help stall the spread of disease in the Libby colony.
“We’re preparing for the worst and hoping for the best,” she said.
The state is still awaiting results from samples taken this spring from two caves in western Montana. Sites in Glacier National Park and Eureka tested negative for the fungus. Guano samples from the North Shore Wildlife Management Area were inconclusive.
A site in Bonner County, Idaho also tested positive for white-nose syndrome this year.
As part of ongoing monitoring efforts, state wildlife officials are encouraging residents to contact their local field office if they find a dead bat between the months of December and May. Bat mortalities in the winter are a strong indicator of white-nose syndrome. Officials noted that residents need not report bat mortalities during other times of the year.
While white-nose syndrome only affects bats, other diseases, including rabies, can be transmitted from bats to people. Use protective gear, including gloves, when handling a bat carcass. Secure the carcass in a Ziploc bag or another disposable airtight container for transport to the nearest wildlife office.
State biologists are also seeking landowners to assist with bat monitoring efforts on their property. If interested, contact state bat biologist Shannon Hilty at shannon.hilty@mt.gov.
Reporter Hailey Smalley can be reached at 758-4433 or hsmalley@dailyinterlake.com.
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