Different wintering strategies of two Palearctic migrants in West Africa - a consequence of foraging strategies?

The wintering strategies of Pied Flycatchers Ficedula hypoleuca and Willow Warblers Phylloscopus trochilus in their West African winter quarters were compared. Pied Flycatchers arrived early in the season (September) and stayed in the study area throughout the winter. They were territorial and showed a high return rate. Intraspecific relationships were mostly expressed by territorial behaviour. Interspecific relations seemed to be unimportant. Willow Warblers arrived relatively late (November) and were absent from the area for some weeks in January and February, a behaviour which was interpreted as itinerancy. Willow Warblers were non-territorial and never returned to a site. Willow Warblers usually moved through the area in monospecific or mixed-species flocks. Habitat and microhabitat choice of these species were similar but in feeding ecology they differed by the higher diversity of feeding substrates and feeding techniques of Pied Flycatchers. The differences in the winter strategies are explained by the ability of Pied Flycatchers to defend a territory because of their diversity in foraging behaviour, whereas Willow Warblers are more specialized and are therefore forced to be more mobile to find their patchily distributed food.