Modified Cave Entrances: Thermal Effect on Body Mass and Resulting Decline of Endangered Indiana Bats (Myotis sodalis)


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Publication Date

June 1993


Entrances to many caves occupied by the endangered Indiana bat (Myotis sodalis) have been modified to control human access. We show that modifying cave entrances can degrade the bats’ winter habitat, we demonstrate one mechanism by which this damage occurs, and we document a restoration experiment. We compared a large bar population in an unmodified cave with a small, reduced bat population in a cave with warm winter temperatures resulting from an entrance wall that impeded air exchange. In the modified cave, mean winter temperature at the hibernation site was 5.0° C higher than in the unmodified cave, bats entered hibernation at a 5% higher body mass, bats lost 42% more mass and the frequency distribution of late‐winter mass was truncated, with no bats weighing less than 5.4 g. The results describe unacceptable extremes for hibernation: subfreezing temperatures and warm temperatures causing mass‐loss rates of more than 0.009 g/day. Over a decade following removal of the entrance‐constricting wall, the population increased from 2,000 to 13,000 bats. Previous recommendations, based on common‐sense observation, to open blocked cave entrances are confirmed by this study. The similar case of Coach Cave, Kentucky, offers the potential for recovery of 100,000 Indiana bats.


Indiana Bats, Bats, Myotis Sodalis, Bat Decline

Document Type



Conservation Biology, Vol. 7, no. 2 (1993-06-01).