Data from: The relative response of songbirds to shifts in song amplitude and song minimum frequency

Anthropogenic noise presents a problem for acoustic communication in animal taxa around the world. Many animals respond by modifying their acoustic signals, sometimes along multiple axes, such as song structure, redundancy, or amplitude. To date, no study has assayed the relative response of animals to multiple axes of signal variation, such as song structure and song amplitude, associated with anthropogenic noise levels. To investigate the impact of multiple potential adaptations to anthropogenic noise on targeted receivers, we manipulated song amplitude and song minimum frequency of white-crowned sparrow (Zonotrichia leucophrys) songs. We used a 2 × 2 factorial design of playback experiments to measure male territorial responses to songs that were relatively quiet or loud in relation to typical Z. leucophrys songs and with lower or higher minimum frequencies within the range of natural Z. leucophrys songs. Males responded more strongly to louder songs than to quieter songs and more strongly to lower than to higher minimum frequency songs, with the strongest responses to louder songs with relatively lower minimum frequencies. These results indicate that whether or not increasing amplitude or increasing minimum frequency is more effective at increasing signal transmission distance in anthropogenic noise, increases in signal amplitude increase signal salience in male–male interactions. Thus in the context of territoriality and sexual selection, an increase in song amplitude can compensate for losses in signal salience due to higher minimum frequency. An increase in only song minimum frequency in the context of low frequency anthropogenic noise could be maladaptive.人为噪音（anthropogenic noise）对全球范围内各类动物类群的声学通讯构成了严峻挑战。诸多动物会通过调整自身声学信号来应对这一问题，调整维度往往涵盖多个方面，例如鸣唱结构、信号冗余度或振幅。截至目前，尚无研究针对人为噪音背景下，动物对鸣唱结构与鸣唱振幅等多维度信号变异的相对响应展开测定。为探究人为噪音背景下多种潜在适应性策略对信号接收者的影响，我们对白冠带鹀（Zonotrichia leucophrys）的鸣唱振幅与最低频率进行了操控处理。我们采用2×2析因设计（factorial design）的回放实验（playback experiment），测量雄鸟对以下四类鸣唱的领域响应：相较于白冠带鹀典型鸣唱，振幅相对偏高或偏低，且最低频率处于其自然鸣唱频率范围内的偏高或偏低区间。实验结果显示，雄鸟对高振幅鸣唱的响应强度显著高于低振幅鸣唱，对最低频率偏低的鸣唱响应强度显著高于最低频率偏高的鸣唱；其中，振幅偏高且最低频率偏低的鸣唱可引发最强的领域响应。本研究结果表明，尽管在人为噪音环境中，提升鸣唱振幅与提升最低频率在增加信号传播距离方面的有效性尚不明确，但提升信号振幅可增强雄鸟间互动中的信号显著性。因此，在领域行为与性选择的背景下，提升鸣唱振幅可弥补因最低频率升高而导致的信号显著性损失。若仅在低频人为噪音环境下提升鸣唱最低频率，则可能产生适应不良的后果。