By Heather Kaarakka, Conservation Biologist – Bureau Natural Heritage Conservation, Wisconsin Department of Natural Resources
Near the University Bay Marsh at Picnic Point lies critical habitat for an important and elusive animal – the little brown bat. Little brown bats, which consume human and agricultural pests, have experienced significant declines from the deadly bat disease, white-nose syndrome (WNS), which arrived in Wisconsin in 2014, but surveys of roost sites like the bat house at Picnic Point show that bat populations may be stabilizing and possibly even starting to recover post WNS. Thanks to evening emergence surveys conducted by volunteers, students, and Wisconsin Bat Program (WBP) personnel, wildlife managers have been able to track not only the little brown bat colony at the Picnic Point bat house, but also at over 100 other roost sites around the state. Summer roost sites like bat houses are critical habitat for bats because they provide safe, warm places for bats to give birth and raise their young. Prior to the arrival of WNS, the Picnic Point bat house was home to 50-350 bats depending on when the emergence survey was completed.
Understanding the temperatures preferred by bats and whether roost sites can get too hot for bats is an important piece of the management puzzle because it can influence how we build and place bat houses in the future to help bolster recovering populations. To begin investigating temperature ranges preferred by bats, WBP placed dataloggers inside occupied bat houses in spring before bats arrived. The data loggers recorded temperature every hour over the summer. We also conducted emergence counts to see if bats abandoned roosts if they got too hot. The datalogger at the Picnic Point bat house showed that during the day, the inside of the box did not get significantly hotter than outside. However, at night the box stayed warmer than outside indicating that the bat house mediated temperature throughout the night. We didn’t conduct nightly emergence counts at Picnic Point so we were unable to pair temperatures with the number of bats present, but we will likely continue this project in 2020.
Even though we couldn’t pair temperatures and number of bats, the temperatures recorded in the Picnic Point bat house still represent conditions at an occupied roost and add to our understanding of bat habitat. After WNS arrived in the state, the colony at Picnic Point declined by approximately 80% but the only reason we can estimate this and watch for recovery is because of volunteers and students donating their nights to watching bats. You too can get involved in bat monitoring and help survey Picnic Point’s bats! You can join the UW Bat Brigade if you’re a student, or help the Wisconsin Bat Program gather information about bats around the state!