Are Echo-Reflective Cues Effective to Attract Bats to Newly Placed Artificial Roosts?

The availability of suitable roosts is an important factor affecting the viability of bat populations. In Europe and North-America, the installation of artificial roosts is a standard conservation measure to mitigate the loss of tree cavities or crevices at buildings. How quickly artificial roosts, such as bat boxes, are adopted, depends on how easily the bats can find them, and on their suitability for roosting. While there is some information about how the design of bat boxes influences their occupancy, it is unknown to what extent the use of bat boxes depends on their detectability. In this experimental field study, we studied the roost selection behavior of three forest-living bat species. We investigated whether attaching an external echo-reflector to bat boxes influenced the time until the bats discover a box or the total number of discovered boxes, which are proxies for detectability. We also assessed whether this modification improved the occupancy of newly placed boxes, as a proxy for their attractiveness. As a result of a previous study, all studied bat colonies were familiar with the echo-reflector as an indicator for the suitability of bat boxes as a day roost. For each species, we compared between boxes with and without an echo-reflector, the number of boxes discovered, the number of days elapsed until discovery, the number of subsequent visits, and the number of days that each box type was used as day roosts. Myotis bechsteinii and Myotis nattereri discovered, visited and used more unmodified boxes than boxes with echo-reflectors. Plecotus auritus did not show differences in behavior with regard to the box types. Our results show that attaching an echo-reflector to newly placed artificial roosts does not improve their discovery and subsequent occupation, even when bats are already familiar with this cue as an indicator of suitability. We discuss the implication of our findings for bat conservation.