Do Weather and Lunar Cycle Influence the Decision of Juvenile Reed WarblersAcrocephalus scirpaceusto Perform Post-Fledging Nocturnal Flights Over the Natal Area?

Abstract

Abstract. Many juvenile Reed Warblers perform nocturnal flights before the onset of the autumn migration. In our study we tested the hypothesis that the decision by juvenile Reed Warblers to perform such flights over the natal area during the post-fledging period depends on weather conditions and the phase of the lunar cycle. We analysed the data on nocturnal movements of 26 birds radio-tagged near their natal site on the Courish Spit (SE Baltic coast). We infer from our results that the decision in juvenile Reed Warblers to take off on a nocturnal flight over the natal area is triggered by intrinsic stimuli and depends only very slightly on environmental conditions. Comparison of these data with a previous study of the effect of weather and the lunar cycle on long-distance nocturnal pre-migratory flights by juvenile Reed Warblers suggests that the motivation to leave the natal area at night increases under good visibility and conditions favourable for flight.