Biologists are studying a rare species of bat found at Mammoth Cave National Park that could hold the secret to warding off White Nose Syndrome, a fungal disease that has decimated bat species globally.
WNS impacts hibernating bats, pulling them out of their winter hibernation and forcing them to utilize vital fat reserves, leading to starvation and death. The disease was first recorded at Mammoth Cave in 2012 and first appeared in the United States in 2007.
Since then, the disease has almost completely wiped out several species at the national park, including the once-common northern long-eared bat.
“That’s one of four species that have really been hit the hardest on this park by White Nose Syndrome, and that’s the one that’s been hit the worst, it’s like a 99% decline,” said Steve Thomas, a lead biologist with the Cumberland Piedmont Network.
CPN works with a network of 14 national parks on inventory and monitoring of natural resources, including plant and animal species on park property.
Thomas has been leading bat research across the U.S. for around 30 years.
He says other species, like the little brown bat, have seen similar impacts from the disease at an alarming rate. Their population has dropped by roughly 95%.
“I remember one cave in the park, we used to see between five and seven hundred of them, and now it’s down to six, the last time I counted there,” Thomas said.
The battle against White Nose Syndrome
While many of these species have seen dramatic declines, others like the Rafinesque’s big-eared bat have seen little to no effect from the disease despite carrying the fungal spores on their fur and wings.
Rick Toomey, a cave specialist at Mammoth Cave, said there are many theories on why the Rafinesques have proven immune to the normally deadly disease.
“There are ideas that it may be the microbiome that’s on their skin, their immune system may work differently, because they wake up so frequently it may never have a chance to take hold because they’re constantly turning their immune system back on,” Toomey said.
He explained that the bats most impacted typically do not pull themselves out of hibernation. The leading theory is that their immune systems slow down dramatically while in that state, leaving them susceptible to the disease.
To track winter populations, the researchers split their work into two main categories. “We have caves that Rafinesque’s big-eared bats hibernate in, and then we have an entirely separate set of caves that are what we call myotis caves,” Toomey explained.
Myotis caves house bats that have seen the greatest population declines from WNS. Those caves are checked on even years, with non-myotis caves being checked on odd years.
“So, the last time I was at this cave we’re going to now, it was two years ago, it was 2023,” Thomas said.
Biologists with the Cumberland Piedmont Network are conducting their research in partnership with Mammoth Cave National Park, using various means of tracking bat populations in caves across the park.
While bats hibernate in winter, researchers use non-invasive methods to conduct population counts. They enter caves where there are known colonies, using click-counters and digital photographs to count individual bats in each colony.
Inside a remote cave roughly 40 minutes from the Mammoth Cave Visitor’s Center, the research team found 210 Rafinesque’s big-eared bats and five big brown bats, two species that have shown resistance to White Nose Syndrome.
Those population counts were on par with others in the past, showing those species continued resistance. With this research, and other population counts conducted across CPN’s seven-state range, the team hopes to uncover the secrets to those species’ immunity.
“There was so much field work and data collection involved at this park that they hired interns to assist with it. And same for the summer bat monitoring, that one needs more people, so we also have interns dedicated to that,” explained Clare Bledsoe, a biologist with CPN.
Those summer counts provide a more in-depth look at the health of individual bats. Researchers capture the bats in an expansive mist net as they exit the caves to feed. Once captured, vital information like species, sex, general health and measurements is collected before releasing the bats.
While rare across the U.S., Rafinesque populations at Mammoth Cave are a reliable representation of one species winning the battle against WNS.
Biologists say the research is ongoing and will likely take several years to discover what sets Rafinesques and species like them apart. They’re hopeful that with continued work, recovery efforts for impacted species can begin before key species are completely wiped out.
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