Pa’s Little Brown Bat, decimated by a pathogen, is now endangered

Doug Wentzel, program director at Shaver’s Creek Environmental Center in Huntingdon County, has spent more than two decades caring for wildlife, including songbirds, birds of prey and bats. 

Over the last decade, Wentzel has seen bats become much rarer at Shaver’s Creek due to the devastating effect a deadly fungal infection has had on bat species in Pennsylvania and across the country.

The fungus, which causes a powdery, white growth on the faces of infected bats, is believed to have originated in upstate New York where it killed hibernating bats in a cave-dwelling colony before spreading bat-to-bat across the United States. 

Little Brown Bat with White Nose Syndrome (Photo courtesy Ryan von Linden/New York Department of Environmental Conservation).

Now, the Little Brown Bat, once the most common species of bat in Pennsylvania, is on the state endangered species list.

The pathogen, now known as White-Nose Syndrome (WNS), has decimated bat populations across North America and has a mortality rate of more than 90%.

“I will never stop missing the bats that we lost,” Wentzel said, noting that nearly all of Pennsylvania’s Little Brown Bat population has been wiped out by WNS. 

A 2021 study from the United States Geological Survey found that WNS killed more than 90% of the nation’s northern long-eared, little brown and tri-colored bat populations in less than a decade. 

Over time, the fungus breaks down the fragile skin tissue of bats’ wing membranes, rendering them unable to fly and hunt. According to wildlife rehabilitators, many bats affected by WNS die from starvation or freeze to death. 

“To have the most common species of bat in Pennsylvania reduced to endangered status in a decade is phenomenally sad.”

Gabriela Chavarria, science advisor to the director at the U.S. Fish and Wildlife Service, testified at a 2011 hearing on WNS that the agency was “concerned” about the impact the illness would have on bat populations across the country. 

“The sudden and widespread mortality associated with this disease has never before been observed in any of the more than 1,100 species of bats known to science,” Chavarria said, calling WNS “the greatest challenge bat conservation has ever faced.  

In the twelve years since Chavarria’s testimony, things have only grown worse for the Little Brown Bat. 

Wentzel was working at Shaver’s Environmental Center as an intern in 1990. At the time, the center had several bat boxes on its 7,000-acre property. 

He recalls hosting night walks to the bat boxes, where visitors would eagerly wait to see the resident bat colony, made up of around 2,000 Little Brown Bats, emerge to hunt just after sunset.  

“When I started here there were bats,” Wentzel said. “It was very memorable.”

But WNS would devastate the colony in less than a decade. 

In a solemn, but rhythmic cadence, Wentzel recalls the bat colony’s losses: 

2009: 1,200,

2010: 900,

2011: 151,

2012: 69,

2013: 9,

2014: 2,

2015: 1.”

The staggering losses recorded at Shaver’s Creek are not unique. 

Bat researchers currently estimate that Pennsylvania has lost between 98-99% of its Little Brown Bat population due to WNS. 

“It took nine years to really collapse the whole colony,” Wentzel said. “To have the most common species of bat in Pennsylvania reduced to endangered status in a decade is phenomenally sad.”

With no cure identified for WNS, Wentzel admitted: “It’s not looking too good for little brown bats.”

Environmental Impact

Steph Stronsick is a licensed bat rehabilitator and the Executive Director of the Pennsylvania Bat Rescue, a team of wildlife experts and bat experts determined to reeducate the public about the important role Pennsylvania’s nine native species of bats play in the ecosystem.


“It’s not just one species being affected,” Stronsick said, adding that insect populations could go unchecked without bats around to feed on them.

“Bats, without them, we have a lot of insects,” she said.

To date, Stronsick said there isn’t data on what the immediate ecological impacts of a declining bat population have been, but she said an unchecked insect population could wreak havoc on crops and Pennsylvania’s $132.5 billion agriculture industry.

Stronsick said she is particularly concerned about how human-caused climate disruptions will affect the spread of WNS in migratory bat species. 

“WNS is going to continue to be an issue as species change their range,” Stronsick said.

Of the Pennsylvania species vulnerable to WNS, the Little Brown Bat, the small bat species found in the commonwealth, is most at risk.

Even if the Little Brown Bat miraculously survives WNS, researchers estimate that it will take more than 400 years for the population to return to pre-WNS numbers. That figure, however, is based on the assumption that no other ecological disaster will hinder the species’ survival. 

Coping with Loss and Finding Reason to Hope

On the grounds of Shaver’s Creek Environmental Center are five bronze statues of extinct bird species. 

Staring at the statue of the extinct passenger pigeon, Wentzel reflects on the grief he feels for the Little Brown Bat and other species on the brink of extinction. 

“It’s hard to be a naturalist,” he said. “It’s a new loss every day.”

When asked how he stays optimistic despite the near-constant barrage of bad news, Wentzel asked: “What‘s the other option?”

“I don’t think I could ever stop caring,” Wentzel added. “I’m not alone and I feel that. Maybe that’s where the hope comes in?” 

While Stronsick also grieves for the lost bats, she said the resiliency of bats gives her hope that they can survive WNS. 

“They can overcome a lot of things,” Stronsick said. “It’s just amazing.” 

A Little Brown Comeback?

Nearly a decade after WNS caused the collapse of the bat colony at Shaver’s Creek, Wentzel is happy to report that bats are again occupying the bat boxes on the northeast corner of the property. 

“We’re back to counting again,” Wentzel said, smiling. “The fight’s not over.”

Approximately two dozen bats are currently residing in the boxes, he said. 

Stronsick and Wentzel said that people can support their local bat populations by planting native plants, reducing their use of chemical pesticides, and contacting their local wildlife rehabilitation center if they find an injured bat. 

“They’re not all gone,” Stronsick stressed, “It’s not just about saving the individuals it’s about saving the population.”

Originally published at,by Cassie Miller

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