Environmental changes caused by urbanization and noise pollution can have profound effects on acoustic communication. Many organisms use higher sound frequencies in urban environments with low-frequency noise, but the developmental and evolutionary mechanisms underlying these shifts are generally unknown. We used a common garden experiment to ask whether changes in minimum song frequency observed 30 years after a songbird colonized an urban environment are a consequence of behavioural flexibility. We captured male juvenile dark-eyed juncos, Junco hyemalis thurberi, from two populations (urban and mountain) soon after they reached independence (aged 25-40 days), raised them in identical indoor aviaries and studied their songs at an age of 3 years. We found that the large population difference in minimum frequency observed in the field persisted undiminished in the common garden despite the absence of noise. We also found some song sharing between the common garden and natal field populations, indicating that early song memorization before capture could contribute to the persistent song differences in adulthood. These results are the first to show that frequency shifts in urban birdsong are maintained in the absence of noise by genetic evolution and/or early life experiences.

中文翻译：

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城市鸟鸣：在一个普通的花园实验中，城市殖民者的最低歌唱频率保持不变

城市化和噪声污染引起的环境变化会对声学通信产生深远的影响。许多生物在具有低频噪音的城市环境中使用更高的声音频率，但这些转变背后的发育和进化机制通常是未知的。我们使用了一个普通的花园实验来询问在鸣禽在城市环境中定居 30 年后观察到的最小鸣叫频率的变化是否是行为灵活性的结果。我们在两个种群（城市和山区）独立后不久（25-40 天）捕获了雄性黑眼 juncos Junco hyemalis thurberi，在相同的室内鸟舍中饲养它们，并在 3 岁时研究它们的歌曲. 我们发现，尽管没有噪音，但在野外观察到的最小频率的巨大种群差异在公共花园中仍然没有减弱。我们还发现了普通花园和出生野外种群之间的一些歌曲共享，表明捕获前的早期歌曲记忆可能导致成年后歌曲的持续差异。这些结果首次表明，通过遗传进化和/或早期生活经历，在没有噪音的情况下，城市鸟鸣的频率变化得以维持。