Evaluating an Acoustic Method for Estimating Trends in Bat Summer Colony Counts with AudioMoth Recorders

Valerie M. Eddington^{1, 2*}, Sonja E. Ahlberg^{1, 2}, Vona Kuczynska³, Easton R. White¹, and Laura N. Kloepper^{1, 2}

¹Department of Biological Sciences, University of New Hampshire, Durham, NH 03824. ²Center for Acoustics Research and Education University of New Hampshire, Durham, NH 03824. ³US Fish and Wildlife Service, Missouri Ecological Services Field Office, Columbia, MO 65203. ^*Corresponding author.

Journal of North American Bat Research, Special Issue 1 (2025):59–74

Abstract
Passive acoustic monitoring for bats has become a common method to determine species presence and activity levels. However, current acoustic methods are ineffective for monitoring species abundance at large summer colonies. We used synchronized acoustic and thermal-imaging data collected at 6 colonies of Myotis grisescens (Gray Bats) and found a significant positive relationship between acoustic energy and number of emerging bats. Our findings reinforce that acoustics have the potential to estimate population sizes of summer bat colonies. Additionally, we examined ultrasonic amplitude variance across 19 AudioMoth devices at 5 different gain settings and found significant differences among devices and settings. Further exploration into device variability and bat behavior are necessary to develop a robust model of population estimates using acoustic energy.

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