MODIFIED CAVE ENTRANCES - THERMAL EFFECT ON BODY-MASS AND RESULTING DECLINE OF ENDANGERED INDIANA BATS (MYOTIS-SODALIS)

Entrances to many caves occupied by the endangered Indiana bat (Myotis sodalis) have been modified to control human access. We show that mod ifying cave entrances can degrade the bats' winter habitat we demonstr ate one mechanism by which this damage occurs, and we document a resto ration experiment We compared a large bat population in an unmodified cave with a small, reduced bat population in a cave with warm winter t emperatures resulting from an entrance wall that impeded air exchange. In the modified cave, mean winter temperature at the hibernation site was 5.0-degrees-C higher than in the unmodified cave, bats entered hi bernation at a 5% higher body mass, bats lost 42% more mass, and the f requency distribution of late-winter mass was truncated, with no bats weighing less than 5.4 g. The results describe unacceptable extremes f or hibernation: subfreezing temperatures and warm temperatures causing mass-loss rates of more than 0.009 g/day. Over a decade following rem oval of the entrance-constricting wall, the population increased from 2000 to 13,000 bats. Previous recommendations, based on common-sense o bservation, to open blocked cave entrances are confirmed by this study . The similar case of Coach Cave, Kentucky, offers the potential for r ecovery of 100,000 Indiana bats.