Charlton Benjamin D
School of Biology and Environmental Science, University College Dublin (UCD), Belfield, Dublin, Ireland.
PLoS One. 2015 Oct 14;10(10):e0138670. doi: 10.1371/journal.pone.0138670. eCollection 2015.
Determining the information content of animal vocalisations can give valuable insights into the potential functions of vocal signals. The source-filter theory of vocal production allows researchers to examine the information content of mammal vocalisations by linking variation in acoustic features with variation in relevant physical characteristics of the caller. Here I used a source-filter theory approach to classify female koala vocalisations into different call-types, and determine which acoustic features have the potential to convey important information about the caller to other conspecifics. A two-step cluster analysis classified female calls into bellows, snarls and tonal rejection calls. Additional results revealed that female koala vocalisations differed in their potential to provide information about a given caller's phenotype that may be of importance to receivers. Female snarls did not contain reliable acoustic cues to the caller's identity and age. In contrast, female bellows and tonal rejection calls were individually distinctive, and the tonal rejection calls of older female koalas had consistently lower mean, minimum and maximum fundamental frequency. In addition, female bellows were significantly shorter in duration and had higher fundamental frequency, formant frequencies, and formant frequency spacing than male bellows. These results indicate that female koala vocalisations have the potential to signal the caller's identity, age and sex. I go on to discuss the anatomical basis for these findings, and consider the possible functional relevance of signalling this type of information in the koala's natural habitat.
确定动物叫声的信息内容能够为了解声音信号的潜在功能提供宝贵的见解。发声的源 - 滤波器理论使研究人员能够通过将声学特征的变化与发声者相关身体特征的变化联系起来，来研究哺乳动物叫声的信息内容。在此，我采用源 - 滤波器理论方法将雌性考拉的叫声分类为不同的叫声类型，并确定哪些声学特征有可能向其他同种个体传达有关发声者的重要信息。两步聚类分析将雌性叫声分为吼声、咆哮声和音调拒绝声。其他结果表明，雌性考拉叫声在提供有关特定发声者表型信息方面的潜力有所不同，而这些信息可能对接收者很重要。雌性咆哮声不包含关于发声者身份和年龄的可靠声学线索。相比之下，雌性吼声和音调拒绝声具有个体独特性，并且老年雌性考拉的音调拒绝声的平均、最低和最高基频始终较低。此外，雌性吼声的持续时间明显较短，并且与雄性吼声相比，具有更高的基频、共振峰频率和共振峰频率间距。这些结果表明，雌性考拉叫声有可能传达出发声者的身份、年龄和性别。我接着讨论这些发现的解剖学基础，并思考在考拉自然栖息地中传递这类信息可能具有的功能相关性。
