The affected bats are mostly little brown bats (Myotis lucifugus), among the most common North American bats. Other affected bats include the endangered Indiana bat (Myotis Sodalis), the northern long-eared bat (Myotis septentrionalis) and the eastern pipistrelle (Perimyotis subflavus). The bats live year round in the general area of study and usually hibernate each winter in the same caves.

Buckles and colleagues are conducting postmortem exams of organs and tissues and testing for signs of inflammation, bacteria, viruses and toxins. So far, the researchers do not yet know what is causing the massive casualties, Buckles said. “We have some good leads. We are continuing to look for infectious causes and are developing protocols to assess the bats’ metabolic states. They may not have enough fat to make it through the winter,” she said.

Many of the sick bats have a white fungus growing on their faces, are very thin and are congregating near to the cave entrances, a habit of ill bats. But it is “unprecedented” to find so many sick bats grouped near cave entrances, said Buckles. In two caves the researchers studied last year — that together had an estimated 18,000 bats — up to 97 percent died. The caves found this year may hold between 150,000 and 200,000 bats, many of them sick.