Data from: Higher songs of city birds may not be an individual response to noise

It has been observed in many songbird species that populations in noisy urban areas sing with a higher minimum frequency than do matched populations in quieter, less developed areas. However, why and how this divergence occurs is not yet understood. We experimentally tested whether chronic noise exposure during vocal learning results in songs with higher minimum frequencies in great tits (Parus major), the first species for which a correlation between anthropogenic noise and song frequency was observed. We also tested vocal plasticity of adult great tits in response to changing background noise levels by measuring song frequency and amplitude as we changed noise conditions. We show that noise exposure during ontogeny did not result in songs with higher minimum frequencies. In addition, we found that adult birds did not make any frequency or song usage adjustments when their background noise conditions were changed after song crystallization. These results challenge the common view of vocal adjustments by city birds, as they suggest that either noise itself is not the causal force driving the divergence of song frequency between urban and forest populations, or that noise induces population-wide changes over a time scale of several generations rather than causing changes in individual behaviour.

多项观测已在多种鸣禽物种中证实：栖息于嘈杂城市区域的种群，其鸣唱最低频率显著高于环境更安静、开发程度更低区域的匹配对照种群。然而，这种鸣唱频率分化的成因与具体机制至今尚未明晰。本研究以大山雀（Parus major）——首个被发现人为噪音与鸣唱频率存在关联的物种——为研究对象，通过实验验证了鸣唱学习阶段长期暴露于噪音环境，是否会使其鸣唱最低频率升高。此外，本研究还通过在背景噪音条件改变时同步监测鸣唱频率与振幅，探究了成年大山雀对背景噪音水平变化的鸣唱可塑性。实验结果表明，个体发育阶段的噪音暴露并未使其鸣唱最低频率升高。与此同时，研究发现鸣唱定型后的成年大山雀，在所处背景噪音条件发生改变时，未对鸣唱频率或鸣唱使用模式做出任何调整。上述结果对城市鸟类鸣唱调整的主流认知提出了挑战：研究结果提示，要么噪音本身并非驱动城市与森林种群鸣唱频率分化的因果因素，要么噪音是在数代种群的时间尺度上引发群体层面的改变，而非仅引起个体行为层面的变化。