Hundreds of threatened bats hibernate at an abandoned copper mine in Orange County
For weeks, researchers have been stationed outside an abandoned copper mine in Orange County, waiting for bats. The mammals gather at the site to mate in the fall, before heading into the shafts to hibernate for the winter.
State and federal agencies are interested in what bats are doing here because the mines are Superfund sites, and clean up projects in Vershire and Corinth have finally received funding, decades after they were first listed.
Before those projects can begin, the U.S. Environmental Protection Agency needs to make sure their plans won’t harm any endangered species, like some of Vermont’s bats that have gathered at the copper mines since as early as the 1930s, according to historic records.
“As they were abandoned from mining practices, bats moved into them and found out that these mine shafts are a great trap for air that can then stay at a pretty consistent temperature throughout the winter,” Alyssa Bennett, a biologist with Vermont Fish and Wildlife, explained on a call last month.
In past years, state scientists have spotted big brown bats, little brown bats, northern long-eared bats and eastern small-footed bats in these caves. Eastern small-footed bats in particular have thrived at this site, while their numbers have plunged elsewhere in the state.
“Over half of the overwintering population that we know of for the species for the state is in this one site,” Bennett said.
For all of these species, the mines are important because there are only a few dozen known hibernation sites in Vermont, where air trapped underground stays around 30 to 50 degrees year-round.
“Bats need that range in order to use their hibernation behavior, which is bouts of torpor to make it through the winter,” Bennett said.
This strategy to conserve energy means bats are especially vulnerable to disturbance — they can lose up to 5% of their body fat every time they wake up. That’s one reason white nose syndrome has been so deadly for hibernating bats across the state and country.
“They naturally arouse every couple weeks, but what we see with white nose syndrome is that they’ll arouse up to every couple days,” Bennett said. “That’s why those bats die, they ultimately just starve.”
The disease killed off most of the bats that used to hibernate at the Elizabeth mine, in Strafford. “We have hardly seen any bats there at all,” said Bennett. At the other copper mines, little brown bats and northern long-eared bats have been decimated by the disease — state officials counted 14 little brown bats at one site during surveys last winter, down from over 150 bats before the disease arrived, and they didn't find any northern long-eared bats.
For the same reason that white nose syndrome kills bats, intrusions from people can be deadly — every time someone enters a cave during the winter, bats can wake up and burn through their energy stores.
“It doesn’t take many events for them to not have enough fat to make it through the winter,” said Bennett.
“We did see at this site — we’ve seen when we go underground in the winter, dead eastern small-footed bats at the entrance and signs of human disturbance.”
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Lexi Krupp is a corps member with Report for America, a nonprofit national service program that places journalists in local newsrooms to report on under-covered issues and regions.