Bats that Roost Together Get White Nose Syndrome and Die Together

White Nose syndrome is a newly introduced disease caused by the fungus Geomyces destructans, which appears to have recently been introduced into North America from Europe and was first diagnosed in 2006. The disease gets its name due to the white fungal growth on the muzzle and wings seen on hibernating bats.

Little Brown Bat infected with Geomyces destructans

Once infected, the bats routinely rouse during typical times of torpor when they normally are conserving energy. This unfortunately ends with the bats going through excessive weight loss and eventual starvation in winter months, when they cannot find food to sustain this activity. The mortality rate in some colonies is as high as 95%.

Now, a study published in the July 2, 2012 edition of Ecology Letters has linked the social interactions of various bat populations to rates of infection from G. destructans.

Sociality, density-dependence and microclimates determine the persistence of populations suffering from a noval fungal disease, white-nosed syndrome

The authors of the articles examined colony sizes of 120 different populations across 6 different species of bat in the northeastern United States. They did this by utilizing colony counts issued by trained biologists in state natural resource agencies during the typical months of Hibernacula over various years from 1979 to 2010.  This allowed for population growth measurements both before and after the fungus was introduced into the population.

The team found that infection rates of WNS was not based solely on population size, but more closely related to population roosting density and socialization rates of the bats. This information can then be used to extrapolate which species are at the most risk of severe population decline and potential extinction.

All sample populations decreased in growth after WNS infection and 32 of the 120 groups actually became locally extinct. Bats that routinely roost solitarily, such as the tricoloured bats, were noted to only have severe infections during times when the bats were drawn into larger groups such as overwinter roosting. This lead the teams to conclude that while they would be a loss of population size, the overall population could stabilize once the animal population density became low enough to allow for more the bats to roost more spaced out from one another. Bats such as the little brown bat however are known to roost regularly in large close knitted colonies. These bats are not likely to stabilize in decline once hitting a lower population size, and instead continue the spiral until extinction.

With this study we can determine which species of bat populations are at the most risk of extinction once infected with g. destructans, and with that knowledge we can adjust our tactics of fighting a powerful pathogen to those groups that are in the direst situations.

Photo credit: Alan Hicks, NY Department of Environmental Conservation