Acoustic characterization of bats from Malta: setting a baseline for monitoring and conservation of bat populations

Abstract

Bioacoustic research has made several advancements in developing systems to record extensive acoustic data and classify bat echolocation calls to species level using automated classifiers. These systems are useful as echolocation calls give valuable information on bat behaviour and ecology and hence are widely used for research and conservation of bat populations. Despite the challenges associated with automated classifiers, due to the interspecific differences in call characteristics of bat species found in the Maltese Islands, the use of a quantitative and automated approach is investigated. The sound analysis pipeline involved the use of an algorithm to clean sound files from background noise and measure temporal and spectral parameters of bat echolocation calls. These parameters were then fed to a trained and validated artificial neural network using a bat call library built from reference bat calls from Malta. The automatic classifier achieved an overall correct classification rate of 98%. This high correct classification rate for reliable species identification may have benefitted from the absence of typically problematic species, such as species in the genus Myotis, in the analyses. This study’s results pave the way for efficient and reliable bat acoustic surveys in Malta in aid of necessary monitoring and conservation by providing an updated bat species list and their echolocation characteristics.

Keywords:

• Acoustics
• chiroptera
• conservation
• Malta

Acknowledgements

Data were collected with the help of the various members of the Conservation Biology Research Group (University of Malta), including Emily Stanbrook and Laura Barth. Thanks are also due to BICREF NGO volunteers namely Joanna Lass, Hugo Derozier and Xavier Grandjean. We thank Gregory Mifsud and Edward Borg for writing the algorithm script in MATLAB and Bernard Mifsud for reviewing the script. Many thanks go to Dr. Joseph Vella for his helpful comments and assessment of the algorithm. We would like to thank two anonymous reviewers for their helpful comments on earlier versions of the manuscript.