Bats that hibernate together may go extinct altogether, ecologist suggest, due to an ongoing fungal plague.

White-nose syndrome, caused by the fungus Geomyces destructans, has killed roughly 5.7 million North American bats since its 2006 discovery in a New York state cave.

In the current Ecology Letters journal, ecologists led by Kate Langwig of Boston University, and Marm Kilpatrick of the University of California, Santa Cruz, report more gregarious bat species suffer more severely from infections of the fungus and that two bat species look headed for extinction. White-nose syndrome spreads from bat-to-bat, infecting hibernating ones and sapping their reserves over winter. Many end up leaving caves during winter to hunt for food, dying in the cold of starvation.

"Bats clustering together during hibernation obviously plays a role in the contagion," Langwig says. "That's likely bad news for the most social ones."

So far, the U.S. Fish and Wildlife Service reports that bat species in 19 states have been detected with the syndrome, as far west as Missouri and as far south as Alabama. In the new study, Landwig and colleagues looked at sociability and mortality among six affected species: Big brown, Eastern small-footed, Northern long-eared, Indiana, Tri-colored and Little brown bats. Prior to 2006, all of their populations were increasing.

The study looked at bats hibernating in caves in New York, Vermont, Connecticut and Massachusetts from 1979 to 2010, with little brown bats the most common.

"From our analysis, things look really bad for two species, Indiana bats and Northern long-eared bats," Langwig says, given mortality rates and limited reproduction rates. An endangered species, the Indiana bats have continued to hibernate together in clusters that appear to leave them more likely to suffer infection, the team finds. More solitary, the Northern long-eared bats appear "particularly susceptible" to the infection, she says.

Remarkably, little brown bats appear to be roosting in more solitary fashion since the onset of the syndrome, the paper suggests, which may mitigate against extinction. Two other bat species, Eastern small-footed and Big brown bats, are not increasing their population size but appear to be holding steady. Tri-colored bat populations also appear more stable.

"I think this is a good study, looking at population trends with more rigor than past ones, but we have to be cautious because we do not have complete data on these species from prior to the onset of white-nose syndrome," says Jeremy Coleman of the U.S. Fish and Wildlife Service. The study examines cave conditions, suggesting that drier, colder caves may see less bat mortality, perhaps due to the fungus preferring warm or moist settings. "One real thrust of many studies is on the applied side, looking for cave conditions that may help (bat) survival," Coleman says.

Along those lines, The Nature Conservancy has announced it will erect an artificial bat hibernation cave in Tennessee to provide bats a haven from the fungus and test out approaches to treating the syndrome. "That is a really promising approach, where researchers can do a lot of research in an artificial setting that we can't do in a cave or even a mine," Coleman says.