Data from: Sexual and natural selection in the evolution of extended phenotypes: the use of green nesting material in starlings

Although sexual selection is typically considered the predominant force driving the evolution of ritualized sexual behaviors, natural selection may also play an important and often underappreciated role. The use of green aromatic plants among nesting birds has been interpreted as a component of extended phenotype that evolved either via natural selection due to potential sanitary functions, or via sexual selection as a signal of male attractiveness. Here we compared both hypotheses using comparative methods in starlings, a group where this behavior is widespread. We found that the use of green plants was positively related to male-biased size dimorphism, and that it was most likely to occur among cavity-nesting species. These results suggest that this behavior is likely favored by sexual selection, but also related to its sanitary use in response to higher parasite loads in cavities. We speculate that the use of green plants in starlings may be facilitated by cavity nesting, and was subsequently co-opted as a sexual signal by males. Our results represent an example of how an extended phenotypic component of males becomes sexually selected by females. Thus, both natural and sexual selection are necessary to fully understand the evolution of ritualized behaviors involved in courtship.Life history and morphological traits of starlingsRubalcaba_et_al.cs