Contrasting use of space by two migratory Afro-Palearctic warblers on their African non-breeding grounds

In migratory birds, constraints due to breeding are relaxed during the non-breeding season and thus, social behaviours and spatial associations are potentially more directly coupled to food resources and habitats. Use of space and territorial behaviour has rarely been studied in Afro-Palearctic migrants. Variation in strategies could exist among species within the same habitat because of differences in foraging, diet and microhabitat. We compare use of space and association with conspecifics in Common Chiffchaffs Phylloscopus collybita and Subalpine Warblers Sylvia cantillans at a non-breeding site in northern Senegal using radio telemetry and playback experiments. Home ranges of Chiffchaffs were larger and overlapped more than those of Subalpine Warblers. Though Chiffchaffs were often close together, we found no signs of spatial association among individuals in either species. Chiffchaffs showed no clear pattern of territorial response to conspecific song; whereas, playback elicited a territorial response in most Subalpine Warblers. Our results suggest species-specific differences in use of space that might reflect differences in foraging ecology and microhabitat.