Monday, 28 November 2016

Estimating colony sizes of emerging bats using acoustic recordings.

2016 Mar 9;3(3):160022. doi: 10.1098/rsos.160022. eCollection 2016.

Author information

  • 1Department of Biology, Saint Mary's College, Notre Dame, IN 46556, USA; Department of Neuroscience, Brown University, 185 Meeting Street, Providence, RI 02912, USA.
  • 2Department of Neuroscience , Brown University , 185 Meeting Street, Providence, RI 02912, USA.
  • 3National Marine Mammal Foundation , 2240 Shelter Drive #204, San Diego, CA 92106, USA.
  • 4Department of Biology , Saint Mary's College , Notre Dame, IN 46556, USA.


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.


acoustic monitoring; bats; population census