Melanin-based ornament darkness positively correlates with across-season nutritional condition

Sexually dimorphic ornamental traits are widely regarded as indicators of nutritional condition. However, variation of nutritional condition outside the reproductive and the ornament production seasons has rarely been considered, although it affects the generality of information content, especially for ornaments that may be used across the year. We measured several indicators of migratory and moult condition in male and female blackcaps (Sylvia atricapilla) during their autumn migration, and quantified their crown reflectance. We detected robust correlations between migratory and moult condition indices, and the correlation structure was similar in the two sexes. Furthermore, the across-season measure of body condition was positively related to the darkness of the black crown in males, while being unrelated to reflectance traits of the reddish crown in females. Our results reinforce the possibility that some melanin-based ornaments may be year-round indicators of individual quality via their dependence on nutritional condition.

性二态装饰性状（sexually dimorphic ornamental traits）通常被视作个体营养状况的指示因子。然而，鲜有研究关注繁殖期与装饰性状形成期之外的营养状况波动，尽管这类波动会影响信息含量的普适性，对于全年可能被使用的装饰性状而言尤为如此。本研究在黑顶林莺（Sylvia atricapilla）秋季迁徙期间，对雌雄个体的迁徙与换羽状况的多项指标进行了测定，并量化了其冠羽的反射光谱特性。研究发现迁徙与换羽状况指标间存在稳健的相关关系，且该相关结构在雌雄个体间保持一致。此外，跨时期的身体状况指标与雄性黑色冠羽的色度呈显著正相关，但与雌性红褐色冠羽的反射光谱特征无关联。本研究结果进一步支持了这一可能性：部分基于黑色素的装饰性状，可通过与营养状况的关联，成为全年可用的个体质量指示因子。