Feather nest decoration decreases conspecific brood parasitism rate in spotless starlings, Sturnus unicolor

Conspecific brood parasitism is a reproductive tactic in which a female lays an egg in the nest of a conspecific host. This 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’ proposes that white feathers in a nest may affect conspecific brood parasitism rates as they repel visitors to nests in several passerine species, perhaps by indicating a recent predation event. In this study, we tested this hypothesis in the spotless starling, an altricial passerine. Following an observational study that confirmed the natural nest decoration 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 visited less by intruders and parasitized less than nests without feathers. This result suggests an effect of feathers on host nest selection by spotless starling parasites. Parasites may, for example, use feathers as a cue to recent predation or as an indicator of the nesting stage to synchronize their laying with that of the host. Further research is needed to determine whether all feathers have the same impact and whether host females can select the best feathers for defending their nest.