From traditional to geometric morphometrics: a novel approach in bat bioacoustic analysis

Acoustic sampling and analysis are key for bats’ ecological, evolutionary and behavioural studies. However, in bat families such as Vespertilionidae and Phyllostomidae, which exhibit similar echolocation shape pulses, identification using traditional frequency and duration parameters may face limitations. We evaluated the effectiveness of geometric morphometrics in bioacoustics analysis compared to traditional acoustic characterisation in bats. A sample of 384 recordings from 38 species along an altitudinal gradient in Mexico were analysed. The analysis was conducted separately for three bat groups: insectivorous (five families), Vespertilionidae alone, and Phyllostomidae. Each pulse was analysed using two approaches: a geometric morphometrics protocol using the R package SoundShape and the manual measurement of four traditional acoustic parameters: maximum, minimum, and peak frequency and duration. We observed the variance in pulses for each group using Principal Component Analysis (PCA) for both acoustic analysis techniques, and we assessed the performance of each method to discriminate species through Canonical Variates Analysis (CVA). Geometric morphometrics demonstrated pulse reclassification percentages comparable to those obtained using traditional acoustic parameter measurements. However, the results highlight the potential of geometric morphometrics for analysing similar pulses by detecting subtle variances, offering a more detailed representation of the pulses in frequency, duration and amplitude.