Will Bats Rebound?
by Mary Thill
Summer makes me miss bats. Like snow in January or apple blossoms in May, bats are more conspicuous in their absence.
I miss their erratic evening feints over the lake and the shadowy clicking overhead as we sit out after dinner. Every now and then something darker than dusk flits by. A bat sighting is now an occasion, something to tell friends about.
Little brown bats are the species that we notice most in the Adirondacks—they are the ones that skim insects above open water. They were New York State’s most common bat until white nose syndrome struck in 2006. (Read more in “Natural Disaster,” from the April 2011 issue of Adirondack Life.) The invasive fungus Geomyces destructans has killed off approximately 90 percent of little brown bats in the state, the New York State Department of Environmental Conservation estimates.
After tracking five years of population decline, a DEC survey of five caves near Albany last winter found an increase from 1,496 to 2,402 little browns in one year. What happens in these winter-hibernation sites is of high interest because Albany is ground zero for the disease in North America. While the fungus continues to radiate outward, taking a large toll as it spreads, scientists watch how bat populations are responding to longer-term exposure.
A report by Boston University Ph.D. candidate Kate Langwig and other researchers published in the September 2012 journal Ecology Letters found an increase in the number of little browns roosting singly in New York, Vermont, Connecticut and Massachusetts hibernacula. Myotis lucifugus more typically cluster tightly. I saw them packed snug as sunflower seeds on the ceilings of pre-WNS mine shafts in the eastern Adirondacks. Now scientists are noticing that some hang apart from other bats or in smaller groups, which may be a factor in slowing spread of the disease.
Also, bats roosting in the coldest and driest parts of caves may be less vulnerable, the report says. The observations are inconclusive but are part of a growing body of knowledge about how white nose syndrome spreads and how wildlife managers might act to slow it.
This winter DEC will survey Adirondack mines and caves, says Carl Herzog, a biologist with DEC’s wildlife diversity unit. The Adirondack count takes place every other year. Before WNS, the Adirondacks had provided key refuge for the already endangered Indiana bat. While there might be stabilization in the count of little brown bats at some sites, Herzog says, “we have no such good news, not even hints in that direction, for Indiana bats. . . . They have declined at every site every year since the disease showed up.”
“The other species of concern,” he says, “that are more affected than even little browns are the northern long-eared bats and the tricolored bats. Both have declined to the point now where we rarely encounter them at all.”
The trend remains bleak for those three species. But it is unusual for a wildlife disease to cause species extinction, Herzog wrote in the Conservationist earlier this year. “Our best hope is that bats will develop immunity to the disease. Even now, some evidence suggests that some bats may be relatively unaffected, either because of an inherent protective benefit from their own immune system or a tendency to engage in more solitary behaviors, or a combination of both. Whatever the case, scientists hope that those bats will pass down the traits to their offspring; then the decline may halt and populations might be able to recover.”