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 the signaller. 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.精细展示行为的表达能够为同种个体提供关于信号发送者自身品质的可靠信息。现有研究预测，繁殖资源或配偶竞争会影响雌雄个体的信号表达，但以往相关文献大多聚焦于雄性行为。无斑椋鸟（spotless starling）便是一个有趣的研究案例：该物种的雌雄个体均会通过装饰巢穴来传递自身状态与社会地位的信号——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。本研究针对繁殖期同种竞争强度，探究雌雄个体的巢饰行为及其关联。我们设置了高密度（HD）与低密度（LD）两种巢箱密度处理，并记录了产卵前添加的绿色植物材料量、孵化时的羽毛数量，以及不同密度处理下的繁殖生产力。结果显示，高密度巢箱中的绿色植物材料量与孵化时的羽毛数量均高于低密度巢箱。此外，高密度组的巢箱繁殖生产力更低。本研究结果表明，调整巢箱密度会提升繁殖资源竞争强度。争夺领地与配偶的雄性个体聚集，会促使它们添加更多植物材料；而针对雄性个体或其他繁殖相关资源的竞争，则会诱导雌性个体添加羽毛。本研究证实，社会环境能够调控雌雄个体的信号行为表达。