Composition and foraging behaviour of mixed-species flocks in two adjacent African woodland habitats: a spatial and temporal perspective

We examined temporal and spatial effects on (1) overall flock composition, and (2) aspects of the foraging behaviour of three bird species commonly participating in mixed-species flocks in mixed and Acacia woodland across the winter season in South Africa. Foraging observations were compared when birds were alone or with conspecifics, against when in mixed species flocks. The two habitats differed with respect to the presence of the Southern Black Tit Parus niger, a leader species in mixed woodland but largely absent from Acacia woodland. Flock species richness within mixed woodland, but not Acacia woodland, increased significantly as the season progressed. Enlarged flock size resulted from a general increase in flocking tendency of all species. At the species level, the Long-billed Crombec Sylvietta rufescens and the Chinspot Batis Batis molitor showed clear feeding benefits within flocks, whereas tits obtained no feeding benefit. Crombecs and batises also changed foraging location when entering mixed flocks by converging on the foraging height of tits in mixed woodland and on each other in Acacia woodland. Furthermore, batises and tits showed marked temporal changes in feeding techniques, due to the changing vegetation structure, a fact that should be considered in future flocking studies. Ostrich 2007, 78(1): 65–7