Individually Specific Call Feature Is Not Used to Neighbour-Stranger Discrimination: The Corncrake Case

In various contexts, animals rely on acoustic signals to differentiate between conspecifics. Currently, studies examining vocal signatures use two main approaches. In the first approach, researchers search for acoustic characteristics that have the potential to be individual specific. This approach yields information on variation in signal parameters both within and between individuals and generates practical tools that can be used in population monitoring. In the second approach, playback experiments with natural calls are conducted to discern whether animals are capable of discriminating among the vocal signatures of different individuals. However, both approaches do not reveal the exact signal characteristics that are being used in the discrimination process. In this study, we tested whether an individual-specific call characteristic – namely the length of the intervals between successive maximal amplitude peaks within syllables (PPD) – is crucial in neighbour-stranger discrimination by males of the nocturnal and highly secretive bird species, the corncrake (Crex crex). We conducted paired playback experiments in which corncrakes (n = 47) were exposed to artificial calls with PPD characteristics of neighbour and stranger birds. These artificial calls differed only in PPD structure. The calls were broadcast from a speaker, and we recorded the birds' behavioural responses. Although corncrakes have previously been experimentally shown to discriminate between neighbours and strangers, we found no difference in the responses to the artificial calls representing neighbours versus strangers. This finding demonstrates that even if vocal signatures are individual specific within a species, it does not automatically mean that said signatures are being crucial in discrimination among individuals. At the same time, the birds' aggressive responses to the artificial calls indicated that the information transmitted by PPDs is important in species-specific call recognition and may be used by males and/or females to evaluate sender quality, similarly like sound frequency in some insect species.

在多种生态情境中，动物依赖声学信号区分同种个体（conspecifics）。当前，针对个体鸣声标识（vocal signatures）的研究主要采用两类方法。第一类方法中，研究者旨在寻找具备个体特异性的声学特征，该方法可获取个体内部及个体间的信号参数变异信息，并开发出可用于种群监测的实用工具。第二类方法则通过开展自然鸣声回放实验，探究动物是否能够区分不同个体的鸣声特征标识。然而，这两类方法均无法揭示鉴别过程中实际被利用的具体信号特征。本研究旨在检验一项个体特异性鸣声特征——即音节内连续最大振幅峰间隔时长（PPD）——是否对夜行性且高度隐秘的长脚秧鸡（Crex crex）的雄性个体区分邻居与陌生个体至关重要。我们开展了配对鸣声回放实验，向样本量为47的长脚秧鸡群体播放带有邻居与陌生个体PPD特征的人工鸣声，且此类人工鸣声仅在PPD结构上存在差异。实验通过扬声器播放鸣声，并同步记录鸟类的行为反应。尽管此前已有实验证实长脚秧鸡能够区分邻居与陌生个体，但本研究发现，针对代表邻居与陌生个体的人工鸣声，其行为反应并无显著差异。该研究结果表明，即便某一物种内存在个体特异性的鸣声特征标识，也并不意味着此类标识必然在个体区分中发挥关键作用。与此同时，鸟类对人工鸣声的攻击性反应显示，PPD所传递的信息对于物种特异性鸣声识别至关重要，且可能如同某些昆虫类群的声频特征一样，被雄性和/或雌性个体用于评估信号发送者的质量。