Acoustic parameters of bat echolocation calls in Zambia : a collaborative effort to develop a call library for non-invasive research and monitoring

Abstract

Passive acoustic monitoring (PAM) of bats enables non-invasive research that improves monitoring efficiency, and can be used for species identification, documenting occurrence and measuring activity levels. However, equipment costs and a dearth of experienced personnel, as well as a lack of local open access reference datasets (call libraries), have limited the study of African bat communities using PAM. This study compiles the first publicly available call library of this scale from Zambia. Echolocation calls were recorded upon release of captured bats during various projects from 2015 to 2023, using full spectrum ultrasound detectors. Acoustic calls from 238 individuals of 22 species were collated. We aimed to determine whether Zambian bat species could be accurately distinguished using acoustic measures. We predicted that some species (or species groups) would be easily identifiable, while other species would have substantial similarities in their calls, which would hinder identification. After considering multicollinearity, we selected five acoustic parameters to analyse the recordings: ‘Frequency of Maximum Power’, ‘Preceding Interval’, ‘Start Slope’, ‘End Slope’ and ‘Ledge Duration’. Principal Component Analysis was conducted to identify parameters that were best able to separate the calls of different functional groups (identified by sonotype) or species. Discriminant Function Analysis was then used to determine the accuracy with which the parameters may be used to acoustically distinguish species or sonotypes. The parameters ‘Start Slope’ and ‘Frequency of Maximum Power’ were the most useful for separating the species considered. It was possible to separate some sonotypes and species with relatively high accuracy. Many species, however, could not be identified with certainty, underscoring the importance of other identification techniques, such as morphological measures or genetic sampling.