White-Nose Syndrome Detected in Bats at Libby Dam

Montana Fish, Wildlife and Parks (FWP) has confirmed the presence of a fungus that causes white-nose syndrome, a disease that can devastate bat populations, in two bats captured at Libby Dam in Lincoln County. 

The disease detection at Libby Dam is the first to occur west of Montana’s Continental Divide. The dam is home to one of Montana’s largest known maternity roosts for little brown myotis and Yuma myotis — two bat species that are highly susceptible to white-nose syndrome. 

White-nose syndrome, named for the visible white fungal growth on infected bats’ muzzles, attacks bats during hibernation, damaging wings and disrupting physiologic processes like heat exchange and circulation. The disease is caused by Pseudogymnoascus destructans, a fungus that grows in cool spaces like the underground caves where bats tend to hibernate. 

Since white-nose syndrome was first detected in the U.S. in 2006, some bat species — including the little brown myotis — have suffered population declines of more than 90%.   

Although bats inhabit most corners of Montana’s diverse landscape, capturing and monitoring them is challenging. Maternity colonies in human-made structures like the Libby Dam visitor center are easier to access and study, FWP Bat Biologist Shannon Hilty explained, which in turn aids research efforts.  

Hilty also explained that larger maternity roosts like the one in Libby Dam are more likely to survive an initial white-nose syndrome invasion and the steep population decline that can follow it.  

“Larger colonies may also serve as a source for smaller colonies within the area, so if we can help these persist, we might be able to help prevent local extirpation,” Hilty said.  

In 2023, FWP expanded bat monitoring efforts to include emergency counts at maternity colonies. Because FWP has only two years of population data, Hilty said the agency cannot yet track whether numbers have declined. Population declines related to white-nose syndrome typically occur one to three years after fungal detection.  

The agency will continue to work with the U.S. Army Corps of Engineers to monitor the Libby Dam’s bats through emergence counts and acoustic bat detector surveys.  

While Hilty noted there is “no quick or easy fix for white-nose syndrome,” she said FWP is working to determine whether implementing management actions at targeted locations like the Libby Dam is the most effective way to prevent local extirpation. 

The fungus that causes white-nose syndrome likely originated in Europe or Asia and was first discovered in the U.S. in New York. Since the initial detection in 2006, the fungus has spread across the country and Canada.  

In addition to the Libby Dam detection, experts recently found the fungus in Bonner County, Idaho — indicating the fungus is spreading into Montana from both eastern and western fronts.  

“Some potential management actions, such as vaccinations, have a clock on them, meaning they’re only a feasible option for a certain number of years after fungal detection,” Hilty said. “That clock is now ticking across most of Montana.” 

Beyond their ecological importance, bats play a critical role in supporting Montana’s agricultural economy. All 15 bat species in the state are insectivores, with a single little brown myotis capable of eating thousands of insects in one evening. This natural pest control helps reduce the need for chemical alternatives. 

“Montana’s bats contribute an estimated $680 million in free pest control each year,” Hilty said. “Globally, bats save farmers billions of dollars annually.” 

But the consequences of white-nose syndrome extend far beyond farms. A 2024 study found that declining bat populations in the northeastern U.S. led to increased pesticide use, as farmers sought alternative ways to protect their crops. The result was a rise in infant mortality rates, highlighting the broad public health implications of declining bat populations. 

“A disease like this can damage our ecosystems, our economy, and, ultimately, have large impacts on the wildlife and people that reside within our state,” Hilty said.

Because white-nose syndrome was first discovered in the northeastern U.S., much of what experts know about the disease is based on patterns observed in eastern bat populations. But Montana’s landscape — and the behavior of its bats — are different. 

Unlike many eastern species that hibernate in caves and mines where they contract the disease, Montana’s bats tend to use other types of winter roosts. 

“There is evidence that suggests bats here are using rock outcrops, badland features, and other natural formations,” Hilty said. “We do not know how bats behave in these environments, and we do not know how [the fungus] will proliferate in them.” 

White-nose syndrome is not known to be infectious to humans or other animals and does not pose a public health risk.   

Nonetheless, FWP requests that climbers and other recreationists take precautions when visiting areas with roosting bats to prevent further spread of the disease. Visitors should remove dirt and mud from shoes and other gear before leaving the site, bag the items, and clean them immediately when they get home.  

Hilter also urged the public to report any unusual bat activity. 

“Anyone who sees a dead or sick bat in wintertime or spring, when bats should be hibernating, should call their local FWP office for further guidance,” she said. “Never handle bats, whether alive or dead.”  

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