BILATERAL SYMMETRY AND SOCIAL-DOMINANCE IN CAPTIVE MALE RED-WINGED BLACKBIRDS

There has been much recent interest in subtle departures from perfect symmetry in bilaterally paired morphological characters, and the exten t to which such departures reflect aspects of individual quality. We u sed data from aviary contests involving pairs of wild-caught male red- winged blackbirds (Agelaius phoeniceus) to test the hypothesis that co mparatively symmetrical males are disproportionately successful in int ra-sexual competition for food. Although paired contestants showed cle ar and consistent differences in competitive ability, there was no ind ication that symmetrical males were competitively superior. Winners an d losers of aviary contests were indistinguishable based on asymmetry measures made on each of four bilateral characters (tarsus length, win g chord, and two epaulet dimensions), and for a fifth character (lengt h of outer retrix), asymmetry differences, though significant, occurre d in the direction opposite to that predicted. Furthermore, there was no detectable association between male competitive ability and a compo site measure that combined asymmetry information across all five chara cters. Our results, in combination with those of several other recent avian studies, suggest that symmetry is generally a poor predictor of social dominance in birds. This finding is inconsistent with the propo sal that symmetry provides a readily obtained, reliable measure of phe notypic quality.