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.精细信号展示的表达可为同种个体提供关于信号发出者个体质量的可靠信息。繁殖资源或配偶的竞争被认为会影响雄性和雌性的信号表达，但以往研究大多聚焦于雄性行为。纯色椋鸟（spotless starling）是一个极具研究价值的范例：该物种两性均会通过装饰巢穴来传递自身状态与社会地位——雄性在繁殖初期会添加绿色植物，而雌性则会在孵化期放置外来羽毛。本研究旨在探究繁殖期内，雌雄两性的巢穴装饰行为与同种竞争强度之间的关联。我们布设了高密度（HD）与低密度（LD）两种巢箱密度处理组，并记录了产卵前添加的绿色植物量、雏鸟孵化时的羽毛数量，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量与雏鸟孵化时的羽毛数量均高于低密度巢箱。此外，巢箱密度更高的组别，其繁殖生产力更低。本研究结果表明，调控巢箱密度会加剧繁殖资源竞争：争夺领地与配偶的雄性聚集行为，会刺激它们添加更多的植物材料；而针对雄性或其他繁殖相关资源的竞争，则会促使雌性添加羽毛。本研究证实，社会环境可对雌雄两性的信号行为表达产生潜在影响。