It was still light out when the first bats began leaving their roost.
One by one, or sometimes in pairs, they swooped from the weather-beaten pine box, just over the heads of several people who had converged in Hinesburg last Thursday to observe the flying mammals. "Oh, my gosh, they're out! They're out!" exclaimed Susi von Oettingen, pulling a tally counter from her jacket pocket and clicking it furiously. "Three, four, five!"
Von Oettingen, a retired U.S. Fish & Wildlife Service biologist, was one of nine volunteers recruited to count Indiana bats, an endangered species on both Vermont and federal lists. For the next hour, the census takers sat in lawn chairs under the roosts and watched their subjects dart into the woods. They swatted away the mosquitoes that the bats feast on.
The bats' habitat, a 301-acre public forest, was conserved when the colony was discovered nearly 20 years ago — just before the onset of the devastating white-nose syndrome. While bats elsewhere have struggled to rebound, the Indiana bats in Hinesburg appear to be thriving. To wildlife experts, the colony's resilience is a testament to how conservation and good land management can help restore a species on the brink.
"There are not a lot of these forest patches left," said Alyssa Bennett, a Vermont Fish & Wildlife Department biologist who organized the bat count. "I think what we're seeing here is land that's been conserved, especially for this bat, is really working."
As their name implies, Indiana bats hail from the Midwest, but they've lived in Vermont for nearly a century. They were listed as a federally endangered species in 1966 — the result of years of human interference in the caves where they overwinter. By the early 2000s, the population of Indiana bats was half of what it had been in the 1960s.
For that reason, bat discoveries are often considered to be significant events, including in Vermont. In the 1990s, authorities closed off a portion of the Green Mountain National Forest to logging after a single Indiana bat was located in a Dorset cave. It took nearly three years to hammer out a plan to allow tree cutting to continue — all for a creature whose body is the size of a human thumb and weighs less than three pennies.
When the bats were discovered in Hinesburg in 2006, it marked the farthest point north and east that the species had ever been found. Members of the Hinesburg Land Trust and other conservation groups worked with state and federal officials to purchase the land, which was being sold by a longtime farming family, and succeeded in 2007, permanently conserving the bats' habitat.
The deal came just before white-nose syndrome began spreading across the region and decimating the local population. The fungus attacks hibernating bats, waking them and sapping their stores of energy and fat. Since arriving in Vermont in 2008, the disease has killed nearly 65 percent of Indiana bats. Where biologists once counted hundreds of the species, they were tallying fewer than 50.
So when Bennett and her team went to catch, release and count the bats in Hinesburg last summer, they were shocked when Indianas instantly flew into their nets. Researchers caught between 700 and 800 that night.
"No other species, just Indiana bat, Indiana bat, Indiana bat," Bennett said. "Which is crazy when you're used to going out on a landscape and catching just the common species."
The colony is mostly made up of mother bats and their pups, who spend summers in Hinesburg. When the weather cools, they zip across Lake Champlain to a mine in New York, where they mate before tucking in for the winter. Bennett, who works closely with New York State biologists, said Indiana bat counts have increased at that mine, whereas the little brown bats that used to hibernate there have all but disappeared.
Bennett is loath to describe where, exactly, the bats dwell out of a desire to protect them, but she said their Vermont habitat is tailor-made for the species. Unlike their little brown cousins, which like to hole up in houses, Indiana bats prefer to roost in trees — particularly dead ones with peeling bark — and there are plenty of them in the Hinesburg forest. The spot is quiet and dark, with no streetlamps and few houses nearby.
The town created a rule book to keep the land attractive to bats. Its 64-page land management plan limits certain activities during the bats' roosting season or bars them altogether if the human intrusion bothers the animals.
Pat Mainer, who chairs the town's Forest Committee, said the thriving colony is proof that these conservation efforts are working.
"I feel that we're very lucky," she said. "If that [land] were developed for housing back in 2007, if that had been subdivided for houses, I assume the bats wouldn't be there."
The bats' impressive numbers have undoubtedly raised their profile. Two enthusiasts, including an artist who lives 100 miles away in Bridgewater, have donated long, narrow bat houses known as "rocket boxes" to the cause. Mounted atop a pole, the boxes give the bats 360 degrees of roosting surface, allowing them to move to warm or cool spots without being exposed to predators.
Bennett has been deputizing teams of citizen scientists to help count bats on summer nights. She hopes the research will eventually show whether the population is staying level or growing.
"I'm hoping we can go here year after year and see what happens with this colony," she said. "It will be really telling."
The early results look promising. Last week, after it became too dark to see, the bat counters packed up their clipboards and walked back to their cars, where they excitedly shared their findings.
Bennett quickly tallied the numbers: 812 total.
Clarification, August 14, 2023. This story was updated to note that the Hinesburg Land Trust worked to conserve the land involved.