THE MOLT OF BARRED WARBLERS SYLVIA-NISORIA IN KENYA - EVIDENCE FOR A SPLIT WING-MOLT PATTERN INITIATED DURING THE BIRDS 1ST WINTER

The moult of Barred Warblers Sylvia nisoria was studied during three w inter seasons in southeastern Kenya at a southward passage site (Nguli a) and a wintering site (Mtito Andei). Most Barred Warblers migrating through Ngulia in November had yet to commence winter moult. These bir ds probably moulted subsequently in winter in northern Tanzania. In De cember, birds were found in heavy moult at Mtito Andei, and some of th ese birds were known to stay throughout the winter. By contrast, most birds reaching southeastern Kenya from late December onwards had alrea dy completed part or all of their winter moult, presumably at stopover sites in northern and eastern Kenya or in Ethiopia. Thus, winter moul t in Barred Warblers takes place mainly in late November and December, either just before or soon after the final leg of autumn migration. I n general, first-year birds renewed all tertials and tail feathers, ab out three to five secondaries per wing and commonly also the outer one to four large primaries per wing. Adults renewed all tertials and tai l feathers, almost all secondaries and only occasionally an outer prim ary. The replacement of relatively fresh juvenile secondaries during t he birds' first winter implies that the split moult pattern of this sp ecies (secondaries, tertials and tail moulted in winter; primaries and tertials in summer) is endogenously controlled.