JUVENILE WING SHAPE, WING MOLT AND WEIGHT IN THE FAMILY SYLVIIDAE

A study of 56 species of Sylviidae occurring in the western Palaearcti c showed a significantly less extensive post-juvenile moult in those s pecies which incur longer migrations to winter quarters than in specie s that migrate short distances, Species with the more extensive post-j uvenile moult also undertook their first full moult in summer compared with the less extensive post-juvenile moult in species with a full mo ult in the winter, In 11 species, young birds had shorter wings and lo wer body mass than adults, These differences produced significantly lo wer wing loadings in young birds compared with adults. Those species u ndertaking a full moult in the winter had significantly more pointed w ings than species with their full moult in the summer. I suggest that this difference is the result of winter-moulting species evolving from the probably basic strategy of a full post-breeding (summer) moult. S ome species, such as the Barred Warbler Sylvia nisoria, may be in the process of changing the full-moult season from summer to winter.