CONTEXT-DEPENDENT EFFECTS OF TAIL-ORNAMENT DAMAGE ON MATING SUCCESS IN BLACK GROUSE

Male black grouse (Tetrao tetrix) may receive damage to their tail ornaments, the lyre, during goshawk predation attempts and during fights with other males. In this study we confirm a previous observation that black grouse males with damaged tail ornaments suffer reduced mating success. In males that held territories on the edge of the leks, tail damage was unrelated to mating success, whereas in central males damage was negatively correlated with mating success. We tested experimentally whether absence of damage is used by females in mate choice. In males with edge territories, intact, control males had higher mating success than males with cut tails, but in males with central territories, lyre cutting had no effect on mating success. These results suggest two interpretations. First, female choice also depends on factors other than tail damage such as position on the lek and dominance. Second, the effect of tail damage is context dependent; in males that otherwise meet females standards (e.g., dominant males), the effect of tail damage is negligible, but in less dominant males, tail damage could be used by females in mate selection. The second interpretation provides an explanation for why the data on unmanipulated and manipulated birds differ. In experimental central birds, factors other than tail damage probably determine male mating success, whereas in experimental edge birds such factors are probably absent and therefore tail damage is relatively more important. In central unmanipulated birds, however, males with natural damage are probably not chosen because tail damage and absence of other attractive traits are correlated. The absence of an effect on peripheral unmanipulated birds may be explained by their overall low mating success.