Identifying unusual mortality events in bats: a baseline for bat hibernation monitoring and white‐nose syndrome research

Bat population trends are particularly affected by adult mortality, especially when large numbers of individuals die, as evidenced by white‐nose syndrome in North America. We obtained baseline mortality data from 318 European hibernacula. Mortality was low and negatively associated with elevation but not with fungal infestation. Mortality events involving more than seven bats at a hibernaculum should be considered unusual, and above this threshold, pathological or microbiological analysis should be carried out. To increase understanding of mortality in bats, there is an urgent need to develop and co‐ordinate national and international programs for monitoring and investigating mortality and diseases.