Pennsylvania bats: Some species headed for extinction?
Pennsylvania's bats have not come back.
After being decimated by white-nose syndrome, cave bats, especially the little brown bat and the northern long-eared bat, continue to show signs of massive decline, experts say.
This is the time of year when the Pennsylvania Game Commission conducts its annual survey of cave bats, which hibernate underground from October through mid-April.
The hibernacula surveys, as they're called, have revealed that while some threatened bat species are surviving and adapting, most of the devastated populations have not recovered.
Winter surveys have shown a mortality rate of 99 percent, while summer roost counts show a decline of 93 percent, said Tammy Colt, Southwest Region diversity biologist with the game commission.
“It could lead to the extinction of some species,” she said. “We lost so many in such a short time span, it would be nearly impossible for them to grow their numbers back up.”
Unlike some mammals, bats do not reproduce in large numbers — females have only one pup per year, Colt said. Juveniles often lead a tenuous existence until they get through their first winter.
Pennsylvania is home to six species of hibernating bats and four species of migratory bats.
White-nose syndrome, a fungus that affects bats while they're hibernating, was first detected in a single cave in New York in 2007. It was discovered in Pennsylvania in the winter of 2008-09 in a half dozen sites in Lackawanna, Luzerne and Mifflin counties, said Greg Turner, superintendent of the game commission's Endangered and Nongame Mammal Section.
The syndrome had spread statewide by 2012 , including Westmoreland County in 2010-11 and Fayette County in 2009-10. Sites with 30,000 bats dropped to the single digits within 90 days, he said.
“Overall, our cave bat population decline is 98.9 percent. It's maintaining at that level,” said Turner, whose survey activities took him to Somerset County on Monday.
Bats infected by white-nose syndrome are unable to hibernate properly, causing them to burn up their winter fat stores and starve to death, Turner said. A white fungus grows on the noses of some infected bats.
The Austin-based nonprofit Bat Conservation International has called the population decline from white-nose syndrome “the most precipitous wildlife collapse of the past century” and Pennsylvania the hardest-hit state.
However, Turner sees a faint glimmer of hope, which he documented in the 2016 book, “Conservation and Ecology of Pennsylvania's Bats” (Pennsylvania Academy of Science).
Turner wrote a chapter showing how some survivors of white-nose syndrome are adapting by hibernating in colder places. The fungus does not thrive in climates where the temperature dips below 38 degrees; bats normally hibernate in temperatures between 44-49 degrees, he said.
“The only sites with a sizeable number of survivors were the ones that were really cold,” Turner said. “There's just a handful of these sites … where we started noticing these survivors. Those sites that are super cold are the only ones where we see bat numbers increasing. Most of the other sites we see are not doing well.”
Bats are using that cold temperature to slow the growth of the fungus and conserve energy, but Turner stops short of calling it a recovery.
“It looks mostly like we've stabilized,” he said.
Colt said there is evidence to suggest that white-nose syndrome is not 100 percent fatal.
“Some little brown bats got it and survived to the next winter and seemed to be OK,” she said. “We don't know if that's because of an immune response or some bacteria that's fighting the fungus.”
The decline in the bat population has serious implications for humans.
Because bats eat insects, bats can reduce everything from mosquito-borne diseases to agricultural pests. The average bat consumes 1,000 to 1,500 insects per night.
Stephen Huba is a Tribune-Review staff writer. Reach him at 724-850-1280, firstname.lastname@example.org or via Twitter @shuba_trib.