Timing of songbird migration: individual consistency within and between seasons

The timing of migration is generally considered of utmost importance for reproduction and survival, and timing is furthermore considered to be under strong genetic control. Th e individual timing of migration is presumably a result of a combination of genetic, phenotypic and environmental factors as well as some degree of randomness. However, potential diff erences in consistency of timing between spring and autumn and between migration strategies are not well studied. Using long-term Danish ringing data, we study such diff erences by correlating date of ringing with date of recaptures for a suite of common migrating passerines in Denmark. We found that individuals marked early in one year tended to be recaptured early in the same season in a following year indicating that individuals time their migration in spring or autumn similarly between years. Th e relationship between spring and autumn migration was overall slightly negative, suggesting that birds arriving early in spring tended to depart late in autumn and vice versa. Th ere were only weak eff ects of geographical location on timing, suggesting that the patterns found are not primarily caused by diff erent populations being involved. Knowledge of individual consistency in migration timing is needed for understanding changes in migration timing. Th e consistent patterns of repeatabilities within and between seasons found here highlight the importance of timing of migration in songbirds.