By: Nick Engelfried
August 27, 2010
Throughout the United States, bats provide valuable services by consuming insects that would otherwise damage crops, spread disease, or simply make summer evenings much less enjoyable. But a growing number of states are starting to see once-common bat species disappear, devastated by a strange fungal disease known as “white-nose syndrome.” In a recent move to slow the spread of the disease, the Bureau of Land Management is recommending closure to the public of caves where bats roost on federal land. The hope is to stop humans from inadvertently spreading the disease from one bat-populated cave to another, and protect bat populations that have not yet been reached by the lethal fungus.
White-nose syndrome was discovered in the United States in 2006, by a cave photographer exploring caves in New York. The fast-spreading fungus is deadly to hibernating bats and is estimated to have killed around a million bats already, so far mostly in eastern states. In Vermont, for example, 95% of the state’s bats have succumbed to white-nosed syndrome. The recent BLM decision to advise cave closures marks that latest effort at containing the disease. After watching bat population in the eastern US suffer from the spread of the fungus, western states are now kicking into gear to try to save their own bats. Earlier this summer the US Forest Service set in place a one-year moratorium on use of all or most caves in five states.
Scientists are still struggling to understand the exact source of the disease, and how bat colonies in the eastern US first became infected with the fungus. It appears that either the fungal spores themselves or some other agent of disease causes bats hibernating during the winter to burn through their stored up fat reserves much faster than normal. Infected bats essentially starve to death and are often found weeks or months later, still hanging from the roofs of caves but covered in a film of fungus. Mortality in affected bat populations usually ranges between 70-90%, so stopping the spread of the fungus to new areas is of utmost importance.
Trying to contain white-nosed syndrome illustrates the challenge involved in addressing risks to threatened posed by disease outbreaks. Though the disease may be a “natural” phenomenon, scientists suggest the syndrome might not have spread as fast or as far as it has were it not for human adventurers unknowingly transporting fungus spores from cave to another on their clothing. Bat species already at risk due to habitat alteration and other human activities are of especially great concern, as their already dwindling numbers could pushed past the brink of extinction by disease. At least one endangered species, the Indiana bat, is among those that have suffered significantly from white-nosed syndrome.
The Center for Biological Diversity, a national environmental group focused on species protection, has urged that bat caves on federal land in all the 48 continental United States be at least temporarily closed to use to prevent contamination. This would present a serious logistical challenge, as the BLM alone oversees 8.4 million acres of land, largely in the west. In states like New Mexico where caving is a popular recreational activity, cave closures are likely to meet with resistance.
But if white-nosed syndrome is allowed to spread to migratory bat species like the Mexican free-tailed bat, it could become still more difficult to control with migrating bats carrying the disease over vast distances. This would add a whole new dimension the challenge of containing the disease. The Center for Biological Diversity and other environmental organizations have praised the BLM’s recommendation that more caves on federal land be closed to recreational activities, but have urged federal agencies to do more to prevent the deadly fungus from reaching new bat populations.
Photo credit: US Fish and Wildlife Service