Wildlife biologists in Vermont have discovered a hopeful sign for the state’s Indiana bat population: One colony, located in Hinesburg, appears to be flourishing.
In the Green Mountain State and nationwide, bats have been suffering from white-nose syndrome for more than a decade, when the disease first appeared and swiftly decimated the populations of several species.
Numbers of Indiana bats in the rest of Vermont have been declining, and the species is federally listed as endangered. But the summer colony, located on conserved land in Hinesburg, contains around 700 of the animals, according to data collected this summer by Alyssa Bennett, a small mammals biologist with Vermont’s Department of Fish & Wildlife.
The colony hibernates across Lake Champlain in New York, Bennett said.
“In Hinesburg this field season, we counted as many as 300 bats in a single roost,” she said. “That is similar to historic numbers at this site, and three times greater than anything we have found in Vermont over the past decade,” when the white-nose disease was first detected in the state.
The conserved land in Hinesburg appears to have contributed significantly to the growth of the Indiana bat colony. Habitat there features a mix of shagbark hickory, dead trees with peeling bark, water and transitions where fields turn to forest, according to Bennett. Bat boxes, which are located at the site, may have helped the animals stay warm and conserve energy during the winter.
Indiana bats are typically found in the midwestern to eastern United States. Vermont is located at the northeastern edge of its range — the Hinesburg colony is the most northeasterly population of Indiana bats. The colony’s success raises new and hopeful questions about the future of the species in the state, Bennett said.
“Are Indiana bats moving further north and east as summers become warmer? Are there other colonies that could benefit from habitat improvement?” she said. “Thanks to this year’s findings, these are the questions we’ll be working to answer in 2023.”
Not all bat populations have made a comeback, however. As the state announced news of the successful Hinesburg colony on Tuesday, the United States Fish & Wildlife Service announced its proposal to nationally list the tricolored bat, whose broad range includes Vermont, as an endangered species due to the ongoing spread of white-nose syndrome.
The proposal came from an in-depth review, which found that the species has declined dramatically across its range, which includes 39 states east of the Rocky Mountains, four Canadian provinces, Guatemala, Honduras, Belize, Nicaragua and eastern Mexico.
“White-nose syndrome has caused estimated declines of more than 90 percent in affected tricolored bat colonies and is currently present across 59 percent of the species’ range,” the Service said in a statement on Tuesday.
The species is dwindling in Vermont, Bennett said.
“Unfortunately, the northern long-eared bat and tricolored bat are the sad stories,” she said. “Tricolored bats — we have them at less than half of the hibernation sites we used to see them in.”
The big brown bat, however, was less affected by white-nose syndrome and is doing well across the state, Bennett said.
In Vermont, populations of the Indiana bat declined by around 65% during the first few years of the disease. Though it’s already federally endangered, in Vermont, the species hasn’t suffered as severely as the tricolored bat and the northern long-eared bat, which is federally threatened with a pending proposal to be listed as endangered.
“We actually thought they were doing pretty well before this disease hit, and there were some whispers about maybe down-listing it to threatened at the federal level,” Bennett said. “But that all went away when white-nose syndrome came.”
White-nose syndrome is an invasive fungus that infects bats’ exposed tissue, causing damage to their noses, wings and tails.
The creatures try to groom the fungus away, but the process rouses them from sleep and steals precious energy. Some emerge from underground to try to find food, but generally in the winter, none is available. The bats most affected by the disease often starve.
In 2008 and 2009, biologists started to see mass mortality in the mammals, with “bats just flying out in the winter and dying on the landscape in January, February, March,” Bennett said. During the first two winters when the disease took hold, populations of three bat species declined by 90%.
Environmental groups are seeking to protect bats against other potential threats in the state, including pesticides used to combat mosquitos in Addison County. In the spring of 2021, the Vermont Natural Resources Council and the Center for Biological Diversity sued the state for allowing the pesticide applications to move forward without a permitting process.
Members of the state’s Agency of Natural Resources have argued that the pesticide doesn’t pose a threat to the bats. The lawsuit is ongoing, according to Michael Harris, director of the Environmental Advocacy Clinic at Vermont Law and Graduate School.