Challenges of Using Bioacoustics to Globally Monitor Bats

As bats are important biodiversity indicators, monitoring their populations is becoming increasingly important to understand the impacts of global change. Bats leak information about themselves into the environment in the form of ultrasonic calls. Using these calls to globally survey bat populations may offer a more efficient alternative or addition to traditional methods for bat monitoring. We identify three of the most important challenges to the development of a global acoustic bat monitoring programme: the robust identification of acoustic signals, the ability to develop meaningful population trends from acoustic activity, and engaging a global audience to take part. We discuss the rapid progress in all three of these areas, for example, development of comprehensive call libraries, quantitative regional tools for call identification, new statistical methods to monitor trends and a resurgence of interest in the public participation in science and monitoring of nature. We also discuss the important gaps in our knowledge and where resources could be best focused to build a global programme. Specifically, tropical areas present a particular challenge: they have high species-richness; species acoustic diversity is poorly documented; call similarity of species is very high, making robust call identification more challenging; and traditionally these areas have had a lower citizen engagement in biodiversity monitoring.