Badge size in collared flycatchers predicts outcome of male competition over territories

Abstract

The evolution of conspicuous coloration is often hypothesized to be driven by sexual selection, where colour traits may function as honest signals of individual abilities in male contest competition and female choice. However, game theory models suggest that colourful badges (i.e. energetically cheap signals) may have no function in sexually selected contests, because the value of the contested resource is too high relative to the costs of fighting. We investigated this assertion by experimentally staging male contests over nest sites (a crucial resource for attracting females) in old (≥2 years) male collared flycatchers,Ficedula albicollisMales with a relatively large white forehead patch (i.e. a condition-dependent plumage trait displayed in male contests) enjoyed a competitive advantage in disputes over experimentally vacated territories. No other measured morphological variable predicted the outcome of such a dispute. Furthermore, the winners of the disputes acquired a female more quickly than did the losers. Thus, our results suggest that the white forehead patch of male collared flycatchers may function as a badge of status that is also used in sexually selected contests over resources. We suggest that this is because the value of the contested territory may be relatively low compared with the cost of fighting when alternative vacant sites exist in the neighbourhood.