Overwinter Weight Loss of Indiana Bats (Myotis sodalis) from Hibernacula Subject to Human Visitation

Overwinter weight loss of Indiana bats (Myotis sodalis) was assessed during the 1989–1990 and 1990–1991 winters at three hibernacula (high, low, and no human visitation) in southern Indiana. We weighed 4264 M. sodalis captured during the autumn swarming and spring emergence periods. Mean spring weights were less than mean autumn weights for males and females in both years. Overwinter weight loss, expressed as a percentage of mean autumn weight, ranged from 15% to 33% and was least at the cave that received no human visitation in three of four sex-year combinations. The magnitude of overwinter weight loss differed among caves in three of four tests, but the effect of cave on weight loss was inconsistent between sexes in both years and between years within sex. Percent weight loss was less at the hibernaculum with low visitation (x̄ = 5.5 visits/winter) than at the hibernaculum with high visitation (x̄ = 378 visits/winter) in two of four sex-year combinations. Increases of populations in both disturbed hibernacula suggest M. sodalis is affected by limiting factors other than, or in addition to, human visitation in winter.