Estimation of organism-wide asymmetry in red-winged blackbirds and its relation to studies of mate selection

Much recent attention has been given to patterns of asymmetry in animals with bilaterally paired characters, and the extent to which such asymmetry might reflect individual quality. Central to much of this research is the assumption that there exists a property of organism-wide asymmetry, and that such a property can be estimated by asymmetry of any given trait. Here we test that assumption using nine characters in male red-winged blackbirds (Agelaius phoeniceus). Although significant concordance in asymmetry among characters confirmed an organism-wide property, that concordance was weak. Consequently, overall asymmetry was poorly predicted by individual characters. Epaulets, a secondary sexual trait, exhibited greater asymmetry than the other traits, but epaulet asymmetry was no better at predicting asymmetry overall. Our results suggest that investigations of the consequences of asymmetry are best restricted to characters where asymmetry is expected to influence performance directly (e.g. traits affecting flight). When individual quality is at issue, a multiple-character approach should be employed.