FLUCTUATING ASYMMETRY AND AUTUMN MIGRATION IN WILLOW WARBLER PHYLLOSCOPUS-TROCHILUS L

Fluctuating asymmetry (FA) reflects the ability of animals to cope wit h environmental and genetic stress. Studies made so far have not yet f ocused and discussed FA's possible effects on migrating birds. In migr ating passerines, FA may reflect an individual's overall condition and dominance during the moulting and pre-migratory period. We studied ho w FA correlates with the timing of migration in one common migratory s pecies, the Willow Warbler (Phylloscopus trochilus L.). In our study, adult females that migrated earlier have more asymmetrical outermost t ail feathers than those migrating later. In males, there was no signif icant correlation between FA and timing of migration. Adult females mo ult later than males and thus may suffer from time constraints in thei r moult before migration. Competition for food resources in contempora ry migrating females may explain why more asymmetrical, probably low q uality females, may have to migrate first.