Juvenile wing shape, wing moult and weight in the family Sylviidae

A study of 56 species of Sylviidae occurring in the western Palaearctic showed a significantly less extensive post-juvenile moult in those species which incur longer migrations to winter quarters than in species that migrate short distances, Species with the more extensive post-juvenile moult also undertook their first full moult in summer compared with the less extensive post-juvenile moult in species with a full moult in the winter, In 11 species, young birds had shorter wings and lower body mass than adults, These differences produced significantly lower wing loadings in young birds compared with adults. Those species undertaking a full moult in the winter had significantly more pointed wings 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. Some species, such as the Barred Warbler Sylvia nisoria, may be in the process of changing the full-moult season from summer to winter.