IS VARIATION IN ORIENTATION RELATED TO FLUCTUATING ASYMMETRY IN MIGRATORY PASSERINES

Fluctuating asymmetry is considered an indirect measure of phenotypic quality and can directly impose high costs in terms of aerodynamics in flying birds. The accuracy of orientation during migration in small p asserines is relevant for survival and reproduction, but patterns of i ndividual variation in preferred directions have received little atten tion. I tested the hypothesis that symmetrical individuals are able to more accurately orient in the correct direction than asymmetrical ind ividuals. Wing, tail and tarsus asymmetry were measured in blackcaps ( Sylvia atricapilla), redstarts (Phoenicurus phoenicurus) and robins (E rithacus rubecula), and the birds were tested for orientation in Emlen funnels, at two stopover sites in N Europe. I then matched individual s for test date, species, sex and age, and assigned them to either of two groups: symmetrical or asymmetrical. The groups were not different in any of the orientation parameters. The lack of effect of asymmetry on orientation may imply that: (i) choices of different direction ref lected different, but equally effective migratory strategies; (ii) sym metrical birds could afford longer stopovers while asymmetrical ones b e less motivated to migrate; (iii) differences in orientation behaviou r would have reflected different quality only under novel or anomalous conditions or (iv) fluctuating asymmetry is not a useful measure of q uality.