In animal communication, receivers benefit from signals providing reliable information on signalers’ traits of interest. Individuals involved in conflicts, such as competition between rivals, should pay particular attention to cues that are “unfakeable” by the senders due to the intrinsic properties of the production process. In bioacoustics, the best-known example of such “index signals” is the relationship between a sender’s body size and the dominant frequency of their vocalizations. Dominant frequency may, however, not only depend on an animal’s morphology but also on the interaction between the sound production system and its immediate environment. Here, we experimentally altered the environment surrounding calling frogs and assessed its impact on the signal produced. Our results show that frogs that are floating are able to inflate their vocal sacs fully and that this change in inflation level is correlated with a decrease of call dominant frequency.

在动物通信中，接收器会从信号中受益，这些信号可提供有关信号发信号员感兴趣特征的可靠信息。涉及冲突的个人（例如竞争对手之间的竞争）应特别注意发送者由于生产过程的固有属性而“无法伪造”的提示。在生物声学中，此类“索引信号”的最著名示例是发送者的身体大小与其发声的主导频率之间的关系。但是，主导频率不仅取决于动物的形态，还取决于声音产生系统与其周围环境之间的相互作用。在这里，我们通过实验改变了青蛙周围的环境，并评估了其对产生的信号的影响。