Dual Utility of a Melanin-Based Ornament in Bearded Tits.

@enA general mechanism to account for the maintenance of sexually selected traits is the armament-ornament model, which predicts that females exploit signals used in male-male aggressive contests. Melanin-based ornaments are good candidates to be dual utility traits because they are usually involved in male-male competition and function as signals of male dominance or fighting ability. Despite this, very few studies have investigated the dual utility of melanin-based plumage traits and results remain generally ambiguous. In this study, we investigated the dual function of a melanin-based trait (the black beard) in the male bearded tit, Panurus biarmicus. In a controlled aviary experiment, beard length was the best predictor of dominance in male-male competition. In a choice experiment, females showed a proximity preference for males whose beard length was experimentally elongated. Our results indicate that beard length plays an important role in both male-male competition and female choice in bearded tits, as proposed by the dual utility model.