Multiple sexual ornaments in satin bowerbirds: Ultraviolet plumage and bowers signal different aspects of male quality

Abstract

Much attention has been devoted to understanding the evolution of elaborate male ornaments and how they may signal male quality. However, the evolution of multicomponent sexual signals remains poorly understood, and past research on this type of signaling has been largely theoretical. Satin bowerbirds, Ptilonorhynchus violaceus, are polygynous, are sexually dichromatic, and construct sexually selected display structures (bowers): a model system for investigating the evolution and signal function of multiple sexual signals. We studied the interrelationship between bower features, plumage coloration, and indicators of male quality in this species. To do this, we located the bowers of male satin bowerbirds in rainforest in Queensland, Australia, and quantified bower quality. We captured the male bower owners and used reflectance spectrometry to objectively measure the plumage coloration of several body regions. We measured various indicators of male health and condition, including the intensity of infection from ectoparasites and blood parasites. Bower quality and male ultraviolet plumage coloration were significantly correlated. By using multiple regression analyses, we show that bower quality predicts ectoparasite load and body size, whereas ultraviolet plumage coloration predicts the intensity of infection from blood parasites, feather growth rate, and body size. Our findings support the multiple messages hypothesis of multicomponent signals: Female satin bowerbirds should assess both male and bower features to choose the highest quality mates.