Data from: Nest decoration as social signals by males and females: greenery and feathers in starling colonies

The expression of elaborated displays provides reliable information to conspecifics about the quality of the signaler. Competition for breeding resources or mates is predicted to affect the expression of signals in both males and females; however, the literature has been typically focused on male behaviors. The spotless starling is an interesting example where both sexes decorate the nest to signal their condition and social status: males add green plants at the beginning of the breeding period, and females place foreign feathers during the incubation period. In this study, we investigate nest decoration by males and females in relation to the intensity of conspecific competition during the breeding period. We distributed nest boxes at either a high (HD) or a low density (LD) and recorded the amount of green plant material added before laying, the number of feathers at hatching, and the breeding productivity under these different density treatments. The amount of green plant material and the number of feathers at hatching were higher in HD than in LD nests. Furthermore, nest boxes at higher density had lower breeding productivity. Our results suggest that manipulating the density of nest boxes increased competition for breeding resources. The aggregation of males competing for territories and mates may stimulate them to add greater amounts of plants, and competition over those males or other resources for reproduction may induce females to add feathers. This study shows that social environment has the potential to influence the expression of signaling behaviors in both males and females.

精致的信号展示可向同种个体传递关于信号发送者自身品质的可靠信息。已有研究预测，繁殖资源或配偶竞争会影响雌雄个体的信号表达，但现有文献通常仅聚焦于雄性行为。无斑椋鸟（spotless starling）便是一个有趣的案例：该物种雌雄个体均会通过装饰巢穴来彰显自身状态与社会地位——雄性在繁殖初期会添加绿色植物，雌性则会在孵化期放置外来羽毛。本研究针对繁殖期内同种竞争强度与雌雄个体巢穴装饰行为的关联展开探究。我们设置了高密度（HD）与低密度（LD）两种巢箱密度梯度，并记录了产卵前添加的绿色植物量、孵化时的羽毛数量，以及不同密度处理下的繁殖成功率。结果显示，高密度组巢箱中的绿色植物添加量与孵化时的羽毛数量均高于低密度组。此外，巢箱密度更高的组别其繁殖成功率更低。本研究结果表明，调整巢箱密度会加剧繁殖资源竞争：争夺领地与配偶的雄性个体聚集，会促使其添加更多植物；而针对雄性个体或其他繁殖资源的竞争，则会诱导雌性添加羽毛。本研究证实，社会环境可对雌雄个体的信号行为表达产生调控作用。