The U.S. Geological Survey reports that the cause of the deaths of thousands of bats at more than two dozen caves and mines in the Northeast states remains a mystery. The illness is known as "white-nose disease" and USGA has issue a bulletin asking wildlife agencies throughout the country to be on alert for and report any suspected cases at bat colonies in their states.
Big brown bat (University of Missouri Extension)
Dead and dying bats with an unknown white substance on their heads and wings have been found at hibernation sites in New York, Vermont, Massacusetts and Connecticut since early 2007. The species affected include the little brown, big brown, northern long-eared and eastern pipistrelle bats. The most common condition has been emaciation, with the bats having little or no body fat.
Scientists say that the white substance may represent an overgrowth of fungi found on bat skin during hibernation and could be an indicator of overall poor health rather than a primary pathogen.