An experimental study of the function of the red epaulettes and the black body colour of male red-winged blackbirds

Abstract

To study experimentally the function of the red epaulettes and the black body colour of adult male red-winged blackbirds, Agelaius phoeniceus, territory owners were removed and replaced with dummies. Intruding males avoided the two mounts with colourful epaulettes compared to the mount with blackened epaulettes and the mount-stand control; intruders also avoided mounts with enlarged epaulettes compared to mounts with normal-sized epaulettes. These results provide the first direct evidence that exposed epaulettes are perceived by intruders as a threat and that larger epaulettes would be more effective signals of threat than are normal epaulettes. Comparisons between the mount with blackened epaulettes and the mount-stand control showed that intruders land closer to the blackened mount than to the control. This result suggests that the conspicuous black body colour of male redwings is not threatening; it is argued that it is a distance signal of attraction that facilitates flock formation.