Sexual selection, colour perception and coloured leg rings in grouse (Tetraonidae)

Studies on birds have suggested that coloured leg rings, resembling ornamental male feathers or bare parts, may increase male attractiveness to females or be important in intrasexual interactions between males. Most of these studies, however, have not considered that the physiology of avian vision is different from that of humans. In consequence, colours that are perceived as similar by a person, may be seen as different by a bird. The effect of leg rings on various aspects of the reproductive behaviour of male black grouse Tetrao tetrix was studied using data obtained from central Finland in 1987–1989. Black grouse males have distinct reddish supra-orbital eye-combs, which have presumably evolved through sexual selection. We used a retinal physiological model of a chicken to compare reflectance spectrograms of orange and red leg rings and eye-combs. The model proposes that, unlike man, grouse are likely to discriminate between spectral reflectance of a red leg ring and eye-comb, but not between an orange leg ring and eye-comb. Black grouse males equipped with orange or red leg rings did not achieve more copulations than males with other colour combinations. Furthermore, we found no significant evidence that males with orange or red leg rings fought more than other males, which would be predicted if ornament-rese mbling leg rings elicit aggression from other males. Results from meta-analyses on the relationship between coloured leg rings and female choice in grouse proved consistent with our findings in black grouse, and suggest that ornament-resembling coloured leg rings do not reinforce mate choice of grouse females.