An experimental test of gating derelict mines to conserve bat roost habitat in southeastern Australia

Abstract

Management of derelict mines to improve subterranean bat habitat and minimise safety risks to the unsuspecting public is occurring more frequently. Many caves and mines around the world have had gates placed at mine and cave entrances as a means of maintaining bat habitat and preventing human access, but there have been few replicated experiments to test their effectiveness. We experimentally tested a staged installation of a template gate at two mines while monitoring another two un-gated derelict mines in southeastern Australia. We recorded changes in numbers, behaviour and the relative species abundance of two bat species (Rhinolophus megaphyllus and Miniopterus schreibersii) before and after the gates were installed. The template gate (20 mm diameter plastic tubing) was installed in three stages, with the initial horizontal bar spacing at 450 mm, followed by a spacing of 300 mm and a final spacing of 125 mm. Bat numbers and behaviour were largely unaffected by bar spacings of 450 mm and 300 mm. The major findings were that immediately after the installation of bars at the final spacing (125 mm gap), numbers of bats declined significantly and a significant increase in the number of aborted exit and entry flights was observed. Detectors proved to be inadequate at quantifying changes in the relative abundance of species. Eleven days after the final installation there were no significant differences between the numbers of bats leaving gated and control mines, suggesting bats had learnt to negotiate the bars after a short period of time. However, flight behaviour was still affected after habituation, especially baulking at the structure when bats attempted to re-enter before dawn. The low replication of mines in the experiment warrants caution in extrapolating this result. Until further gating experiments are carried-out, we recommend site specific monitoring whenever mines are gated.