Structural classification of Wild Boar (Sus scrofa) vocalizations (#6)
A key step in understanding the vocal communication system of a species involves defining its vocal repertoire. Research on domestic pig vocalizations, for example, has led to significant advances in our understanding of communicative function. Despite the close relation to domestic pigs, very little is known about wild boar (Sus scrofa) vocalizations. The few existing studies on this social species, conducted in the 1970âs, relied on visual inspections of spectrograms to quantify acoustic parameters and lacked statistical analysis. Here, we use objective signal processing techniques and advanced statistical approaches to classify 617 calls recorded from semi-free ranging animals. Based on four spectral and temporal acoustic parameters âquartile Q25, spectral flux, spectral flatness and durationâ extracted from a multivariate analysis, we refine and extend the conclusions drawn from previous work and present a statistically validated classification of the wild boar vocal repertoire into four call types: grunts, grunt-squeals, squeals and trumpets. While the majority of calls could be sorted into these categories using objective criteria, we also found evidence supporting a graded interpretation of wild boar vocal communication as acoustically continuous, with the extremes representing discrete call types. Integrating our findings with recent studies on domestic pig vocal behaviour and emotions, we highlight the potential importance of grunt-squeals for acoustic approaches to animal welfare. Our work also establishes a solid foundation and comparative basis for further research investigating both call functionality and the evolutionary origins of vocal production and perception within the genus Sus.