Acceptance of bats to gates at abandoned mines

Caves and abandoned mines provide roosting habitat for bat species that depend on subterranean conditions. Disturbances at caves (e.g., commercial development, recreation) limit their availability to bats, in some cases shifting use to abandoned mines. However, abandoned mines pose public safety hazards and often are gated to reduce risk to humans while maintaining access to bats. To date there is limited information on species-specific acceptance of gates at abandoned mines. We designed our research objectives to determine short-term (1 week) behavioral responses of bats to gating, including gate material and height above ground, mid-term (<1 yr) changes in bat use before and after gate installation, and long-term changes (≥4 yrs) in use and factors influencing species presence. We used an in situ mock gate experiment, comparison of bat use before and after gating, and genetic identification of guano in gated mines for our short-, mid-, and long-term studies, respectively. In our short-term study, bats increased energetically demanding behaviors following gate installation. Although we detected no difference in responses to gate material or height, a less maneuverable bat species circled, collided, and landed more frequently on gates than did an agile species. In the mid-term study, activity remained stable or increased at 73% of mines after gating compared to before gating, although number of maternity colonies decreased. In the long-term study, elevation, portal area, number of mine levels, and entrances were more important than gates in predicting presence of 4 bat species, including 2 subterranean obligates. Species-specific responses to gates appeared based on morphology and vocalization characteristics. Responses to gates shifted from negative in our short-term study to positive in our long-term study. Gate age and mine characteristics were more important predictors of use for most species than gate design. Although the complexity of subterranean habitats makes them difficult to replicate and many factors may influence how bats use this habitat, gates designed for bats (bat-compatible) appear effective for many species.