Animals use acoustic signals for communication, implying that the properties of these signals can be under strong selection. The acoustic adaptation hypothesis predicts that species in dense habitats emit lower‐frequency sounds than those in open areas because low‐frequency sounds propagate further in dense vegetation than high‐frequency sounds. Signal frequency may also be under sexual selection because it correlates with body size and lower‐frequency sounds are perceived as more intimidating. Here, we evaluate these hypotheses by analysing variation in peak song frequency across 5,085 passerine species (Passeriformes). A phylogenetically informed analysis revealed that song frequency decreases with increasing body mass and with male‐biased sexual size dimorphism. However, we found no support for the predicted relationship between frequency and habitat. Our results suggest that the global variation in passerine song frequency is mostly driven by natural and sexual selection causing evolutionary shifts in body size rather than by habitat‐related selection on sound propagation.

中文翻译：

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对雀形目中歌曲频率的全局分析不支持声适应假设，但暗示了性选择的作用

动物使用声音信号进行交流，这意味着这些信号的特性可能处于强大的选择之下。声学适应性假设预测，在茂密的栖息地中，物种发出的低频声音要比在空旷地区的物种低，因为低频声音在密集的植被中的传播要比高频的声音传播得更多。信号频率也可能处于性选择之下，因为它与身体大小相关，并且低频声音被认为更令人生畏。在这里，我们通过分析5,085个雀形目物种（Passeriformes）的峰值歌曲频率变化来评估这些假设。系统发育学分析表明，歌曲频率随体重增加和男性偏向性大小二态性而降低。然而，我们发现没有支持频率与栖息地之间的预测关系。我们的研究结果表明，雀形目歌曲频率的全球变化主要是由自然选择和有性选择引起的，这些选择导致了体型的进化变化，而不是由栖息地相关的声音传播选择引起的。