Townsend's big-eared bat (Corynorhinus townsendii) is a widespread species of special concern that hibernates in large numbers in the lava-tube caves of southeastern Idaho. We measured 24 habitat variables describing landscape-level, physical, and microclimate characteristics of 13 caves and identified at least three that were useful for predicting winter occupancy by C. townsendii. In univariate analyses, distance to ephemeral water was the only variable that significantly predicted occupancy. Temperature and dewpoint were non-significantly higher in occupied than unoccupied caves. Our index of human disturbance was not associated with winter occupancy as observed in other studies. A multivariate (discriminant) analysis identified three characteristics that significantly and best predicted occupancy by big-eared bats in our sample of caves: (1) greater distance to ephemeral water, (2) the presence of a collapse or constriction, and (3) lower mean height. Although not included in our most-predictive multivariate model, high minimum relative humidity was significantly associated with caves that had a collapse or constriction. Our study suggests that both the landscape surrounding the cave and its physical and microclimate characteristics play a role in the suitability of caves as overwintering sites for Townsend's big-eared bats.
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Vol. 34 • No. 1