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.

中文翻译：

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野猪（Sus scrofa）发声的结构分类

摘要 确定一个物种的声音交流系统是分级的还是离散的，需要定义它的声音曲目。在这种情况下，例如，对家猪（Sus scrofadomesticus）发声的研究使我们对交流功能的理解取得了重大进展。尽管它们与家猪关系密切，但人们对野猪（Sus scrofa）的发声知之甚少。在 1970 年代进行的少数现有研究依靠对频谱图的目视检查来量化声学参数，并且缺乏统计分析。在这里，我们使用客观信号处理技术和先进的统计方法对从半自由放养动物记录的 616 次呼叫进行分类。基于四个频谱和时间声学参数——四分位数 Q25、持续时间、频谱通量、和频谱平坦度——从多变量分析中提取，我们改进和扩展了从以前的工作中得出的结论，并提出了一种经过统计验证的野猪声音分类，分为四种呼叫类型：咕噜声、咕噜声、尖叫声和喇叭声。虽然大多数呼叫可以使用客观标准分类到这些类别中，但我们还发现证据支持将某些野猪发声分级解释为声学连续，极端情况代表离散呼叫类型。在声学连续性方面使用基于现代技术和统计的客观标准促进了我们对声音变化的理解。将我们的发现与最近对家猪声音行为和情绪的研究相结合，