Effects of Cave Gating On Population Trends at Individual Hibernacula of the Indiana Bat (Myotis sodalis)

Abstract

Installing gates at cave entrances to protect hibernating bat colonies is a widespread conservation action, particularly for endangered bat species such as the Indiana bat (Myotis sodalis). However, there is surprisingly little evidence on the efficacy of gates for improving population growth rates. We used change-point models to determine the effects of gate construction on Indiana bats. We estimated population growth rates at 20 hibernacula pre- and post-gating and quantified the change in population growth rates after gate installation. Hibernacula with increasing growth rates prior to gate placement all experienced decreased growth rates after installation. For hibernacula with declining growth rates prior to construction, growth rates increased moderately after installation. When weighted by population size, average change in growth rates across all 20 hibernacula was negative. Our results suggest that use of gates at hibernacula with growing populations may relate to unintended declines in growth rates but that, at hibernacula with declining populations, installation of gates may lead to moderate increases in local population growth rates.