Data from: Feather nest decoration decreases conspecific brood parasitism rate in spotless starlings (Sturnus unicolor)

Conspecific brood parasitism is a behaviour in which a female lays an egg in the nest of a conspecific host. This reproductive tactic may be costly for host females, especially in altricial species, as the number of fledglings depends on the parents' capacity to feed them. Consequently, several counterstrategies have evolved, such as nest guarding or egg ejection. The Fear of Feathers Hypothesis has been proposed as one of them. As the presence of white feathers repelled visitors in several passerine species, potentially because they were seen as cues of a recent predation event, it has been suggested that white feathers may also affect conspecific brood parasitism rates. In this study, we tested this hypothesis in the spotless starling, an altricial passerine. We had two predictions: either parasites could favour nests with white feathers, signalling host females of good quality, or they could avoid such nests, as feathers may signal a past predation event. Following an observational study that confirmed the natural decorative behaviour of spotless starlings, we manipulated the content of nests, adding or removing feathers, to determine their effect on parasitism rates. We found no significant effect of white feathers alone. However, we found that nests containing feathers (all colours combined) were less visited by intruders and less parasitised than nests without feathers. This result suggests an effect of feathers in the process of host-nest selection by spotless starling parasites. Feathers may be feared by parasites or simply used as an indicator of the nesting stage to synchronise their laying with the host's laying sequence. Further research is needed to determine whether all feathers have the same impact and if host females can select the most efficient feathers to defend their nest.