Single. By roosting alone, little brown bats may be slowing the spread of the fungus that causes white nose syndrome.
Credit: Al Hicks/New York State Department of Environmental Conservation
There's very little good news with white-nose syndrome, a fungal disease spreading across the United States and Canada. The fungus infects the nose and wings of bats, causing them to wake up early from hibernation and often starve to death. Since the syndrome was first identified among bats in New York in 2006, populations of several species in the northeast have been devastated.
But today researchers report online in Ecology Letters that one species of bat is reducing the risk of extinction, Geomyces destructans, with individual bats hibernating alone rather than in large groups. "That's really positive," says Katie Gillies of Bat Conservation International in Austin, which helped fund the research. In addition, populations in colder, drier caves are experiencing proportionally fewer cases of white-nose syndrome than those located elsewhere. Yet the situation remains dire for the bats, Gillies and others caution, with populations greatly reduced and few tools for wildlife managers to help the bats.
The new study, led by graduate student Kate Langwig of the University of California, Santa Cruz, compiled survey data on all six species of bats in the northeast from before and after the arrival of the fungus. "It's been guesswork until this study," says Paul Cryan, a biologist at U.S. Geological Survey in Fort Collins, Colorado, who was not involved in the research. The conclusions confirmed previous impressions: Two species, big brown bats (Eptesicus fuscus) and Eastern small-footed bats (Myotis leibii), are relatively unimpacted by the fungus. But populations of the Indiana bat (M. sodalis), already on the federal endangered species list, and three other species have taken a nosedive.
Two of the declining species are solitary-roosting bats, which would be expected to have lower rates of transmission than more gregarious bats. And, in fact, the researchers predict that the populations of one type, the tri-colored bat (Perimyotis subflavus), will eventually stabilize. But the northern-long-eared bat (M. septentrionalis) doesn't appear that fortunate: Even though these animals roost alone during hibernation, all 14 populations in the study disappeared within 5 years of the fungus arriving at those caves. The reason isn't known, but Langwig says that the population might have shrunk to a point of no return; the few remaining bats might have been unable to find mates, for example.
The outlook could be just as dire for gregarious bats, which hibernate in cozy clumps of individuals. In theory, the fungus is more likely to wipe out these colonies. After the first few years of the epidemic, research had suggested that little brown bats (M.lucifugus) might vanish from the Northeast within 16 years. But the data gathered by Langwig's group suggest that the worst declines were over by 2009.
To its surprise, the team also noticed a dramatic increase in the percentages of the highly social little brown bats that hibernate alone, ranging up to 75% of a colony. "There's been a real change in behavior," Langwig says. The same loss of sociality is happening to a lesser extent in Indiana bats, but apparently not widely enough to slow their decline.
The researchers also collected data on temperature and humidity within caves used by the two best-studied species: the Indiana bat and the little brown bat. Populations in the colder and drier caves declined less, which makes sense because most kinds of fungus do better in higher humidity. To co-author Marm Kilpatrick of University of California, Santa Cruz, this offers hope that the driest, coolest caves are a refuge from the fungus.
