MIGRATION STRATEGIES OF PALEARCTIC PASSERINES IN AFRICA

Palearctic migrants arrive in the northern tropics south of the Sahara between August and October, as the local rainy season ends. Some spec ies remain in the Sahel and Sudan zones throughout the overwintering p eriod. Others seem unable to tolerate the increasing aridity as the dr y season progresses. These remain in the Sahel and Sudan zones for 1-2 months and then fatten before performing a second migration further s outh, either to dry Guinea savannas in West Africa, or to rainy condit ions in equatorial East Africa or southern Africa, where rains begin i n November. Between March and May, as southern Africa enters its dry s eason and the rains begin in the northern tropics, these movements are reversed, but the passage is much more rapid than in autumn. Birds th at overwinter too far south to reach the Palearctic in a single journe y, put on enough fat to reach the southern edge of the Sahara, where t hey refatten finally for the Saharan or Arabian desert crossing. Palea rctic migrants, Like other birds. moult when it is most favorable to d o so. Some species wintering in the dry northern tropics moult on the breeding grounds before migration, while others moult in winter quarte rs in September-December when these areas are still wet. Species winte ring at equatorial latitudes tend to moult on their northern stopover sites or in their final winter quarters during the same period. Birds wintering in southern Africa moult in their final destination between November and April.