title: Structural Classification of Wild Boar (Sus scrofa) Vocalizations.
abstract: Determining whether a species' vocal communication system is graded or discrete requires definition of its vocal repertoire. In this context, research on domestic pig (Sus scrofa domesticus) vocalizations, for example, has led to significant advances in our understanding of communicative functions. Despite their close relation to domestic pigs, little is known about wild boar (Sus scrofa)vocalizations. The few existing studies, conducted in the 1970s, 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 616 calls recorded from semi-free ranging animals. Based on four spectral and temporal acoustic parameters-quartile Q25, duration, spectral flux, and spectral flatness-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 some wild boar vocalizations as acoustically continuous, with the extremes representing discrete call types. The use of objective criteria based on modern techniques and statistics in respect to acoustic continuity advances our understanding of vocal variation. Integrating our findings with recent studies on domestic pig vocal behavior and emotions, we emphasize the importance of grunt-squeals for acoustic approaches to animal welfare and underline the need of further research investigating the role of domestication on animal vocal communication.
authors.affiliation: Department of Cognitive Biology University of Vienna Vienna Austria.
authors.forename: Maxime
authors.initials: M
authors.lastname: Garcia
authors.affiliation: Department of Cognitive Biology University of Vienna Vienna Austria.
authors.forename: Bruno
authors.initials: B
authors.lastname: Gingras
authors.affiliation: Department of Cognitive Biology University of Vienna Vienna Austria.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Bowling
authors.affiliation: Voice Research Lab Department of Biophysics Faculty of Science Palacký University Olomouc Czech Republic.
authors.forename: Christian T
authors.initials: CT
authors.lastname: Herbst
authors.affiliation: Department of Cognitive Biology University of Vienna Vienna Austria; Department of Psychotherapy and Biopsychosocial Health Danube University Krems Krems Austria.
authors.forename: Markus
authors.initials: M
authors.lastname: Boeckle
authors.affiliation: Réserve de la Haute Touche Muséum National d'Histoire Naturelle Obterre France; Equipe Interactions Cellulaires et Fertilité UMR0085 Physiologie de la Reproduction et des Comportements Institut National de la Recherche Agronomique Nouzilly France.
authors.forename: Yann
authors.initials: Y
authors.lastname: Locatelli
authors.affiliation: Department of Cognitive Biology University of Vienna Vienna Austria.
authors.forename: W Tecumseh
authors.initials: WT
authors.lastname: Fitch
keywords: acoustic communication; graded vocalizations; sus scrofa; vocal repertoire; wild boar