Data from: Sunrise in the city: disentangling drivers of the avian dawn chorus onset in urban greenspaces

Urban systems are known to have a number of effects on avian richness, density, and morphological and behavioral traits. However, no study to date has simultaneously examined the wide range of urban variables in relation to the avian dawn chorus, a complex behavioral phenomenon. Previous studies investigating adjustments of the dawn chorus onset in urban settings have mainly been confined to relationships with noise and light levels. In addition to noise and light levels, in this study we included other potentially related environmental characteristics describing vegetation structure, urban infrastructure, and human activity, all of which have been shown to be drivers of bird diversity in urban areas. We conducted dawn chorus surveys at 38 Los Angeles urban greenspaces and used a classification and regression tree analysis to identify specific urban scenarios that best explained timing differences in the dawn chorus onset. Our results show that light level was the most important variable related to the dawn chorus onset time, in which, counter-intuitively, bird communities in greenspaces with higher light levels had later onsets. In addition, noise was an important factor for the chorus onset in greenspaces with higher light levels. Although our results differ from those of previous studies, these findings highlight the importance of noise and light levels in explaining dawn chorus onset variation, indicating the need for further research in untangling this complex and ecologically important phenomenon.

城市系统已被证实会对鸟类丰富度、种群密度以及形态与行为特征产生多方面影响。然而迄今为止，尚无研究同时考察与鸟类晨鸣（avian dawn chorus）这一复杂行为现象相关的各类城市变量。此前针对城市环境中鸟类晨鸣起始时间调整的研究，主要局限于探讨与噪声和光照水平的关联。本研究除纳入噪声与光照水平外，还新增了描述植被结构、城市基础设施与人类活动的其他潜在相关环境特征；上述因素均已被证实为城市区域鸟类多样性的关键驱动因子。我们于洛杉矶38处城市绿地开展了鸟类晨鸣调查，并采用分类与回归树分析（classification and regression tree analysis）方法，筛选出最能解释晨鸣起始时间差异的典型城市情景。研究结果显示，光照水平是与鸟类晨鸣起始时间关联度最高的变量；且与直觉相悖的是，光照水平更高的绿地内，鸟类群落的晨鸣起始时间反而更晚。此外，在光照水平较高的绿地中，噪声亦是影响晨鸣起始的重要因素。尽管本研究结果与既往研究存在差异，但上述发现仍凸显了噪声与光照水平在解释鸟类晨鸣起始时间差异中的重要性，同时也表明亟需开展进一步研究，以厘清这一复杂且兼具重要生态学意义的行为现象。