Data from: Factors associated with leucism in the common blackbird (Turdus merula)

Leucism is the total or partial lack of melanins in the skin and associate structures (i.e. hair or feathers). Little is known about the factors influencing this chromatic aberration although some local studies suggest that there is an effect of habitat, age and sex. To test these hypotheses and expand our knowledge on leucism, we carried out a large‐scale study using common blackbirds (Turdus merula) as our model species. Given the poor information available on this topic and the variability of methodological approaches, we used three different methods to assess the effect of these variables in the presence of leucism: transects, bird captures and citizen science information (pictures from internet). We found an effect of habitat indicating that there are more leucistic blackbirds in cities than in non‐urban areas. In addition, we found a positive association between presence of white feathers and age providing the first large‐scale support for the progressive graying hypothesis in birds. This chromatic aberration was also influenced by sex, with males showing higher probability of leucism than females, although only for the capture data, indicating that the method used to study this phenomenon can partly influence our conclusions, and therefore suggesting caution when planning future studies in this topic.

白变症（leucism）指皮肤及相关附属结构（即毛发或羽毛）中黑色素的完全或部分缺失。目前学界对影响该色素异常的因素知之甚少，尽管部分区域性研究表明栖息地、年龄与性别会对其产生影响。为验证上述假说并拓展我们对白变症的认知，本研究以乌鸫（Turdus merula）为模式物种，开展了一项大规模调查。鉴于该领域现有研究资料匮乏且不同研究采用的方法学差异较大，我们采用三种不同的研究手段，以评估上述变量对白变症发生的影响：样线调查法、鸟类捕捉采样法以及公民科学数据（互联网上传的鸟类图片）。研究结果显示栖息地存在显著影响：城市环境中的白变症乌鸫数量显著多于非城市区域。此外，我们发现羽毛白色表现与年龄呈正相关，这为鸟类的渐进式羽色变白假说提供了首个大规模实证支持。该色素异常亦受性别因素影响：雄性个体出现白变症的概率高于雌性，但该结果仅基于捕捉采样数据得出。这表明，用于研究该现象的研究方法可能会在一定程度上影响研究结论，因此提示未来开展相关研究时需谨慎设计研究方案。