Bat box occupancy by noctule and brown long-eared bat

Authors: Martijn Boonman & Erik Broer

https://doi.org/10.63269/SJL6014

Abstract: Bats occupying 44 bat boxes in Park Randenbroek, Amersfoort, the Netherlands, were studied during a twelve-year period. The main aim was to determine how much time is needed before bats are using the boxes regularly and if exposition, mounting height and box type influence occupancy. During 16 autumn inspections, noctules (Nyctalus noctula) and brown long-eared bats (Plecotus auritus) were encountered in bat boxes 45 times (n=212) and 11 times (n=54) respectively. Large cylinder-shaped boxes were used more often by noctules and contained more individuals than small cylinder and flat boxes. Noctules preferred bat boxes with a southern exposition but no effect of mounting height was detected within our range of 3.7-7 m. Brown long-eared bats prefered small cylinder-shaped boxes over flat boxes. It took five years until noctules started to use the bat boxes regularly and occupancy increased to 25% after ten years. Noctules seem hesitant to accept new roost sites and /or need a lot of time to discover that bat boxes are suitable roost sites. Guidenes suggest that placing bat boxes one year before logging commences would give bats sufficient time to habituate to the new roost sites. Our study shows that a lot more time may be needed. Occupying new roost sites may be a group decision; this provides a possible further explanation for the long habituation period needed.