Premigratory dispersal of juvenile Willow Warblers<i>Phylloscopus trochilus</i>in southern England

Abstract

The timing of premigratory dispersal of juvenile Willow Warblers, in Southern England, was investigated in relation to fledging and moult periods, and the onset of orientated migration. Retraps of birds ringed as nestlings suggest that young birds remained close to the natal area during the first half of the moult period. Dispersal from the natal area occurred later, coinciding with an influx of birds from elsewhere. Migration on the south‐east coast does not begin until the first birds in southern England have completed moult. It is suggested that during the latter half of the moult period young Willow Warblers disperse in random directions from the natal area, but that they do not initiate their autumn migration until after completion of moult.