It has often been observed that birds sing at a higher pitch in cities and other areas that are polluted with intense low-frequency noise. How this pattern arises remains unclear though. One prevailing idea is that songbirds adjust song frequencies to environmental noise profiles through developmental plasticity via vocal learning. However, the conclusions of previous studies testing this hypothesis are inconsistent. Here we report the findings from two song learning experiments with zebra finches (Taenopygia guttata), in which we exposed young birds to anthropogenic noise during their sensitive vocal learning period. Unlike previous studies that addressed this issue, we did not use constant synthetic noise but natural urban noise with its typical amplitude fluctuations that was broadcast at realistic sound levels. We found that noise-exposed males in neither experiment developed higher pitched songs compared to control males. This suggests that the natural fluctuations between higher and lower noise levels in cities may allow young birds to exploit relatively quiet moments to hear their tutors and themselves, permitting them to make accurate copies of even low-frequency song elements. If animals are to persist in urban habitats, they often must adjust their behavior to the altered conditions. Birds in cities are often observed to sing at a higher pitch, but we are largely ignorant of how this phenomenon arises. We investigated whether low-frequency traffic noise interferes with the song learning of birds so that they develop higher pitched songs. Accordingly, we played back natural traffic noise from urban bird habitats to young birds during their learning period and then analyzed their adult songs. We found that birds that learned their songs in noise did not sing at higher frequencies compared to control males that learned their song with no noise exposure. Our results show that typical traffic noise in cities may not be sufficient to interfere with vocal learning in a way that birds develop higher-pitched songs.

中文翻译：

---

在声音学习期间长期暴露于城市噪音不会导致斑胸草雀的歌曲频率增加

人们经常观察到，在城市和其他受到强烈低频噪音污染的地区，鸟类会以更高的音调唱歌。不过，这种模式是如何产生的仍不清楚。一种流行的想法是鸣禽通过声音学习的发育可塑性来调整歌曲频率以适应环境噪声概况。然而，先前检验这一假设的研究的结论并不一致。在这里，我们报告了两个斑胸草雀 (Taenopygia guttata) 歌曲学习实验的结果，其中我们在幼鸟敏感的声音学习期间将其暴露于人为噪音中。与之前解决这个问题的研究不同，我们没有使用恒定的合成噪声，而是使用具有典型振幅波动的自然城市噪声，并以真实的声级广播。我们发现，与对照雄性相比，在这两个实验中，暴露于噪音的雄性都发出了更高音调的歌曲。这表明城市中较高和较低噪音水平之间的自然波动可能允许幼鸟利用相对安静的时刻来听他们的导师和他们自己的声音，从而使他们能够准确复制低频歌曲元素。如果动物要在城市栖息地中生存，它们通常必须根据变化的条件调整自己的行为。人们经常观察到城市中的鸟类以更高的音调唱歌，但我们基本上不知道这种现象是如何产生的。我们调查了低频交通噪音是否会干扰鸟类的歌曲学习，从而使它们发出更高音调的歌曲。因此，我们在幼鸟学习期间将城市鸟类栖息地的自然交通噪音播放给幼鸟，然后分析它们的成年歌曲。我们发现，与在没有噪音的情况下学习歌曲的对照雄性相比，在噪音中学习歌曲的鸟类并没有以更高的频率唱歌。我们的结果表明，城市中典型的交通噪音可能不足以以鸟类发出更高音调的歌曲的方式干扰声音学习。