Data from: The evolutionary origin of variation in song length and frequency in the avian family Cettiidae

Aspects of bird song have been shown to correlate with morphological and ecological features, including beak and body size, and habitat. Here we study evolution of song length and song frequency among 30 species belonging to the Cettiidae. Frequency is negatively correlated with body size, and song length increases with latitude. Although migration distance correlates with latitude, the association of song length with latitude is only present within the non-migratory species, implying the association is not a consequence of migration. We place these correlations in a historical framework to show that the body size-frequency association arose early in the group, but the latitude-song length association is more evolutionarily labile. We suggest that latitudinal correlates of song length may reflect increased importance of sexual selection by female choice.研究表明，鸟鸣的多项特征与鸟类的形态学、生态学特征存在关联，其中包括喙部与体型大小以及栖息环境。本研究以树莺科（Cettiidae）的30个物种为研究对象，探讨其鸣唱时长与鸣唱频率的演化模式。研究发现，鸣唱频率与体型呈负相关关系，而鸣唱时长则随纬度升高而增加。尽管迁徙距离与纬度存在关联，但鸣唱时长与纬度的相关性仅存在于非迁徙性物种中，这表明该相关性并非由迁徙行为所导致。我们通过演化历史框架分析上述相关性，结果显示体型与鸣唱频率的关联在该类群演化早期便已形成，而鸣唱时长与纬度的关联则具有更高的演化易变性。我们推测，鸣唱时长的纬度相关性可能反映了雌性选择介导的性选择重要性有所提升。