In 2007, a mysterious disease killed thousands of bats in a handful of caves in upstate New York. The culprit, dubbed white nose syndrome, was soon found to be a fungus, Pseudogymnoascus destructans, that thrives in cold, dark, humid environments and can kill entire bat colonies.
In the intervening years, the fungus has spread through the northeast, killing millions of bats. But populations on the coastal islands of Long Island, Martha’s Vineyard, and Nantucket are persisting. Scientists are working to figure out how.
For several years, these populations just weren’t exposed to the disease. White nose syndrome was first documented on Cape Cod in 2013, and not until 2017 on Martha’s Vineyard.
But white nose syndrome is now established on the Vineyard, and yet, northern long-eared bats are still there, and reproducing.
One key may be the relatively milder winters on these islands compared to inland New England. That means bats can go into hibernation, or torpor, later and emerge earlier, reducing their exposure and vulnerability to the fungus.
“That amount of time that they're actually in torpor - when their immune systems are shut down, and when they'd be most vulnerable to the fungus - it is a shorter period of time,” explained Luanne Johnson of Biodiversity Works on Martha’s Vineyard.
Johnson and colleagues on the other islands have been trapping and tagging bats to test this idea, and they’ve found some surprising behaviors adapted to the milder winter weather conditions. For example, the bats are roosting in trees as late as the end of November.
“You wouldn't expect these bats to be in trees that late because temperatures are going down into freezing at that time of year,” Johnson said. “And yet, they're still in trees.”
Johnson says it has also become more common to see periodic warm spells throughout the winter. The island populations are taking advantage of these.
“The bats are, in fact, active and going out and feeding,” she said, “which wouldn't happen in New Hampshire or Vermont, where temperatures are much cooler - and stable at cooler temperatures - and also where the winters are much longer and the bats are deeper into torpor.”
These findings may seem very specific to bats on these coastal islands, but Johnson says she hopes these persistent colonies will eventually be able to rebuild populations in harder hit areas. Understanding how they have made it this long could shape policies, like when and where to cut trees or start construction, that could determine whether these hold-outs remain strong.