White nose syndrome threatens social bats with extinction09/07/2012 09:14:59 Study determines which bats are headed for extinction and finds changes in social behaviour reduce impact of white-nose syndrome - By Tim Stephens
July 2012. The impact on bat populations of a deadly fungal disease known as white-nose syndrome may depend on how gregarious the bats are during hibernation. Species that hibernate in dense clusters, even as their populations get smaller, will continue to transmit the disease at a high rate, dooming them to continued decline, according to a new study led by researchers at the University of California, Santa Cruz. One gregarious species has surprised researchers, however, by changing its social behaviour.
First appeared in New York state in 2006
"All six species were impacted by white-nose syndrome, but we have evidence that the populations of some species are beginning to stabilize, which is really good news," said Kate Langwig, a graduate student at UC Santa Cruz and first author of the paper. "This study gives us an indication of which species face the highest likelihood of extinction, so we can focus management efforts and resources on protecting those species."
Gregarious species suffering badly
"We found that in the highly social species that prefer to hibernate in large, tightly-packed groups, the declines were equally severe in colonies that varied from 50 bats to 200,000 bats, which suggests that colonies of those species will continue to decline even when they reach small population sizes," said co-author A. Marm Kilpatrick, assistant professor of ecology and evolutionary biology at UC Santa Cruz.
Trends in the declines of different bat species since the emergence of white-nose syndrome support these predictions. As populations get smaller, the declines tend to level off for species that roost singly, but not for socially gregarious species.
Little brown bats changing behaviour
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."
The northern long-eared bats in deep trouble
Two species least affected
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.
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.
In addition to Langwig and Kilpatrick, the co-authors 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.
The study, published July 3 in Ecology Letters, examined data from bat surveys between 1979 and 2010, covering a long period of population growth followed by dramatic declines caused by white-nose syndrome.