Weather ultimately affects avian migration. The significance of meteorological variables is relatively well known for flights of migrants and for departure/landing decisions at stopover sites. Success of migration greatly depends on storage of fat and body mass gain at stopovers; however, the influence of weather on refueling at stopovers is surprisingly poorly studied. We tested the hypothesis that body mass change of European Robins during their migratory stopovers is affected by meteorological factors (air temperature, precipitations, surface wind speed), along with other ecological variables. We used data on body mass change in 9743 individuals (5147in spring and 4587 in the fall) captured and recaptured within the same day on the Courish Spit of the Baltic Sea in 1994-2003. Fuel deposition rate in Robins was positively associated with air temperature and with higher amount of precipitation. Wind speed did not influence the refueling efficiency of our study species. Also, fuel deposition rate of Robins was affected by age (higher in adults than in first-year birds), negatively influenced by the number of conspecifics at stopover, influenced by the progress of the season (negatively in spring and positively in fall), and negatively influenced by initial energy reserves of migrants, when birds in poor energy condition were more likely to gain weight than birds with large fuel stores. This study shows that refueling of Robins on migration stopovers is substantially affected by meteorological factors that should be taken in to account for comprehensive understanding of stopover ecology and migration strategy of songbird migrants.
Keywords: Air temperature; Body mass change; Precipitations; Stopover songbirds; Surface wind speed; Weather.