Mixed-species flocks of insectivorous birds (‘bird parties’) in Afrotropical forests and woodlands: a review

Mixed-species flocks of foraging insectivorous birds are found worldwide and have been best studied in the Neotropical region. A survey of the published literature reveals that mixed-species flocks (often termed ‘bird parties’) comprised of 2–30 species and sometimes >70 individual birds are regularly encountered in forest and woodland habitats throughout the Afrotropical region. On mainland Africa, >600 species representing 59 bird families have been reported in such flocks, and for at least 300 species foraging in such flocks may constitute an important part of their feeding activity. In Madagascar, >60 species of 19 families have been recorded in mixed-species flocks, with more than 40 species frequent participants. These foraging parties are dominated by gleaning and sallying insectivorous birds, with other feeding guilds represented by fewer species and individuals. The main hypotheses to explain why birds participate in such flocks emphasise protection from predators while searching for food, and increased foraging efficiency through the disturbance of insects caused by the different foraging activities of flock members. Certain key species may be responsible for the initial formation of the flock. Mixed-species flocks are regarded as particularly vulnerable to disruption by anthropogenic habitat changes, especially to forests, and are thus of special conservation concern. In the Afrotropics, these proposals remain working hypotheses since we currently lack data for a full assessment of the ecological role of mixed-species flocks and their importance in the life history of the participating species.