title: Estimating colony sizes of emerging bats using acoustic recordings.
abstract: The decline of bats demands more widespread monitoring of populations for conservation and management. Current censusing methods are either prone to bias or require costly equipment. Here, we report a new method using passive acoustics to determine bat count census from overall acoustic amplitude of the emerging bat stream. We recorded the video and audio of an emerging colony of Mexican free-tailed bats from two cave locations across multiple nights. Instantaneous bat counts were calculated from the video frames, and the bat stream's acoustic amplitude corresponding to each video frame was determined using three different methods for calculating acoustic intensity. We found a significant link between all three acoustic parameters and bat count, with the highest R (2) of 0.742 linking RMS pressure and bat count. Additionally, the relationship between acoustics and population size at one cave location could accurately predict the population size at another cave location. The data were gathered with low-cost, easy-to-operate equipment, and the data analysis can be easily accomplished using automated scripts or with open-source acoustic software. These results are a potential first step towards creating an acoustic model to estimate bat population at large cave colonies worldwide.
authors.affiliation: Department of Biology, Saint Mary's College, Notre Dame, IN 46556, USA; Department of Neuroscience, Brown University, 185 Meeting Street, Providence, RI 02912, USA.
authors.forename: Laura N
authors.initials: LN
authors.lastname: Kloepper
authors.affiliation: Department of Neuroscience , Brown University , 185 Meeting Street, Providence, RI 02912, USA.
authors.forename: Meike
authors.initials: M
authors.lastname: Linnenschmidt
authors.affiliation: Department of Neuroscience , Brown University , 185 Meeting Street, Providence, RI 02912, USA.
authors.forename: Zelda
authors.initials: Z
authors.lastname: Blowers
authors.affiliation: National Marine Mammal Foundation , 2240 Shelter Drive #204, San Diego, CA 92106, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Branstetter
authors.affiliation: Department of Biology , Saint Mary's College , Notre Dame, IN 46556, USA.
authors.forename: Joel
authors.initials: J
authors.lastname: Ralston
authors.affiliation: Department of Neuroscience , Brown University , 185 Meeting Street, Providence, RI 02912, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Simmons
keywords: acoustic monitoring; bats; population census