Brilliant, diverse colour ornaments of birds were one of the crucial cues that led Darwin to the idea of sexual selection. Although avian colouration plays many functions, including concealment, thermoregulation, or advertisement as a distasteful prey, a quality-signalling role in sexual selection has attracted most research attention. Sexually selected ornaments are thought to be more susceptible to external stressors than naturally selected traits, and as such, they might be used as a test for environmental quality. For this reason, the last two decades have seen numerous studies on the impact of anthropogenic pollution on the expression of various avian colour traits. Herein, we provide the first meta-analytical summary of these results and examine whether there is an interaction between the mechanism of colour production (carotenoid-based, melanin-based and structural) and the type of anthropogenic factor (categorised as heavy metals, persistent organic pollutants, urbanisation, or other). Following the assumption of heightened condition dependence of ornaments under sexual selection, we also expected the magnitude of effect sizes to be higher in males. The overall effect size was close to significance and negative, supporting a general detrimental impact of anthropogenic pollutants on avian colouration. In contrast to expectations, there was no interaction between pollution types and colour-producing mechanisms. Yet there were significant differences in sensitivity between colour-producing mechanisms, with carotenoid-based colouration being the most affected by anthropogenic environmental disturbances. Moreover, we observed no significant tendency towards heightened sensitivity in males. We identified a publication gap on structural colouration, which, compared to pigment-based colouration, remains markedly understudied and should thus be prioritised in future research. Finally, we call for the unification of methods used in colour quantification in ecological research to ensure comparability of results among studies.

中文翻译：

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污染世界中的鸟类颜色：荟萃分析

鸟类绚丽多彩的色彩装饰是引导达尔文产生性选择思想的关键线索之一。尽管鸟类的体色具有多种功能，包括隐藏、体温调节或作为令人厌恶的猎物的广告，但在性选择中的质量信号作用引起了大多数研究的关注。人们认为，有性选择的装饰品比自然选择的性状更容易受到外部压力的影响，因此，它们可以用作环境质量的测试。因此，在过去的二十年里，关于人为污染对各种鸟类颜色特征表达的影响进行了大量研究。在此，我们提供了这些结果的第一个荟萃分析总结，并检查了颜色产生机制（基于类胡萝卜素、基于黑色素和结构）与人为因素类型（分类为重金属、持久性污染物）之间是否存在相互作用。有机污染物、城市化或其他）。根据性选择下装饰品的条件依赖性增强的假设，我们还预计男性的效应大小会更高。总体影响大小接近显着性和负面影响，支持人为污染物对鸟类颜色的总体有害影响。与预期相反，污染类型和颜色产生机制之间没有相互作用。然而，颜色产生机制之间的敏感性存在显着差异，类胡萝卜素的着色受人为环境干扰的影响最大。此外，我们没有观察到男性敏感性升高的显着趋势。我们发现了结构着色方面的出版空白，与基于颜料的着色相比，结构着色的研究仍然明显不足，因此应在未来的研究中优先考虑。最后，我们呼吁统一生态研究中颜色量化所使用的方法，以确保研究结果的可比性。