Surprisingly, however, one highly social species is bucking the trend. The little brown bat, one of the most common bat species in the northeast, appears to be changing its social behavior, going from a species that preferred to roost in dense clusters to one in which most bats now roost apart from other bats. "Our analysis suggests that the little brown bats are probably not going to go extinct because they are changing their social behavior in a way that will result in them persisting at smaller populations," Kilpatrick said.

Another gregarious species, the Indiana bat, continues to hibernate mostly in dense clusters and will probably continue to decline toward extinction, according to Langwig. "Since the appearance of white-nose syndrome, both species have become more solitary, but the change is much more dramatic in the little brown bats," she said. "We now see up to 75 percent of them roosting singly. For Indiana bats, only 8 to 9 percent are roosting alone, which does not appear to be enough to reduce transmission rates."

Even solitary roosting habits may not be enough to save some species, such as the northern long-eared bat. Although it declined less rapidly as its colonies got smaller, 14 populations of northern long-eared bats became locally extinct within two years after the detection of white-nose syndrome, and no populations remained in the study area after five years. In contrast, the populations of tri-colored bats, another solitary species, stabilized at low levels three to four years after disease detection. "The northern long-eared bats may be particularly susceptible to the disease, so they continue to get hit pretty hard even after transmission rates are reduced," Langwig said.

The two species least affected by white-nose syndrome, big brown bats and eastern small-footed bats, are mostly solitary, although occasionally they roost in small clusters. It is not clear why they have been less affected by the disease than other species, Langwig said.

According to Kilpatrick, one possibility is that these species roost in sites where conditions are less conducive to the disease. The study examined the influence of different microclimates within hibernation sites and found that declines were less severe in the drier and cooler sites. "It appears that the driest and coolest caves may serve as partial refuges from the disease," Kilpatrick said.

In addition to Langwig and Kilpatrick, the coauthors of the paper include Winifred Frick, a researcher in ecology and evolutionary biology at UC Santa Cruz; Jason Bried, a graduate student at Oklahoma State University; Alan Hicks of the New York State Department of Environmental Conservation; and Thomas Kunz of Boston University.

Much of the bat population data used in the study was collected in surveys conducted by state agencies during the past 40 years. This research was funded by the National Science Foundation, Bat Conservation International, and the U.S. Fish and Wildlife Service.