MONTPELIER, Vt. — Nearly all the little brown bats that hibernated in a Dorset cave last winter and were tagged with radio chips remained there until spring, an indication they weren't affected by white nose syndrome, a disease that causes bats to wake from hibernation, fly into the frigid winter and die.
Coupled with information from bat maternity colonies in the Champlain Valley that little brown bats appear to be reproducing at rates faster than they are dying, it's a bit of good news in what has been a bleak decade for scientists studying white nose syndrome.
"If we've seen that many bats pass through at the correct time, and behave what we would call normally, that's really exciting," said Alyssa Bennett, a biologist with the Vermont Department of Fish and Wildlife who helped conduct the study.
The bats studied in the Aeolus cave in Dorset were little brown bats, once one of the most common bat species in Vermont. During the early years after the arrival of white nose, up to 90 percent of the species would awaken during what should have been their winter hibernation, fly into the insectless landscape and die. This year, scientists say, as many as 96 percent of them stayed until spring.
White nose syndrome, caused by a fungus, is named for the fuzzy spots it plants on victims' muzzles, wings and tails. It doesn't affect people or other animals but repeatedly interrupts hibernation, sapping their energy and fat stores, which can cause starvation and dehydration.
The disease has spread out of New York into Vermont and has since moved into other parts of the United States and Canada.
While the study shows good news for the little brown bats, the once-common northern long-eared bat, which saw 99 percent of its numbers killed by white nose, are now hard to find in Vermont.
There are at least two locations in New York that have seen similar results, but scientists haven't noticed it in other states affected by white nose, said Jeremy Coleman, the white nose coordinator for the U.S. Fish and Wildlife Service.
Studies are underway to try to determine why the bats are surviving.
Bennett said separate summer studies underway now in the Champlain Valley have found little brown bat maternity colonies that are thriving, and the population is increasing faster than it is declining.
The Vermont cave tagged 442 bats with chips in the fall and then installed electric readers at a point in the Aeolus cave in Dorset where the bats' passage would be recorded and the time noted.
The biologists were looking to see how many bats would leave the cave in the winter, and in all probability die, and how many would wait until their normal spring awakening.
The equipment recorded 192 bats leaving the cave, all but eight at the normal spring emergence time, said Bennett, who worked on the project with Antioch University New England graduate student Morgan Ingalls.
A hole in the study came because the tag reading equipment wasn't turned on until after the bats went into hibernation. It's possible some other bats died deep in the cave, but that's not typical behavior of little brown bats, Bennett said.
And while the bats that were tagged were captured near the opening of the Aeolus cave, biologists believe many of those bats could have hibernated elsewhere and wouldn't have been recorded by the equipment.
But even if all those bats died, which is considered unlikely, the low-end 43 percent survival rate is still an improvement over the early winter survival rates for little brown bats, Bennett said.
The U.S. Fish and Wildlife Service is providing a $60,000 grant so the bats in the Aeolus cave can be studied this coming winter as well.
Coleman and Bennett say it's likely the little brown bats' recovery from white nose will follow its outbreak, but it could be decades before they reach their pre-white nose population levels.
"I don't know why these bats are still there, if it's a resilience that they have for some reason, whether it's behavioral or genetic or they are in some ways just being lucky," Coleman said. "I'm beginning to be a believer despite my pessimism that we are seeing something that is real and hopefully inheritable."