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.