Evaluation of top-down camera trapping for detecting and counting bats emerging from roost boxes.

To face current biodiversity declines, we need to extensively monitor wild animal populations. Wildlife monitoring relies on many different methods, all with their benefits and disadvantages. Among these, camera traps have become the primary tool to conduct wildlife monitoring due to their non-invasiveness and ease of deployment. Despite this, camera traps are hardly ever used to study bats, the second largest mammalian order. Bat surveys could greatly benefit from the use of camera traps, since their roost choices often create defined flight paths that could be exploited by camera traps. Monitoring efforts could also be up-scaled more easily if camera traps prove viable for monitoring bats. Yet, conventional camera traps have been largely overlooked when it comes to the monitoring of bats, mainly due to the assumption that bats are too small and quick in their movement to be reliably detected by them. I evaluated if conventional camera traps can be used to count bats emerging from roost boxes when positioned directly above the roost entrance. I monitored two roost boxes, with slightly different set-ups. The camera trap performance differed substantially between the two roost boxes, with a recall of 0,89 at one box compared to 0,38 at the other. This difference can be primarily associated with differences in camera trap placement and recording settings. My results demonstrate that conventional camera traps can be used to reliably count bats emerging from roost boxes when deployed in a suitable configuration, providing the basis for a minimally invasive and scalable method to monitor bat roost emergences.