Mutualistic and commensal organization of avian mixed-species foraging flocks in a forest of western Madagascar

I examined the feeding rates and foraging niches of seven species regularly participating in heterospecific avian flocks in a deciduous dry forest of western Madagascar in two different social situations, viz. when the species was foraging alone or with conspecifics, and in heterospecific flocks, respectively. The species responded differently to mixed-flocking. A change in feeding sites and/or techniques was found in six species, five of which increased their Feeding rates when foraging in heterospecific flocks. In mixed flocks, they tended to use similar substrates. That such interspecific convergence enhanced feeding rate might be explained by social learning, kleptoparasitism or a beating effect. Benefits gained through these effects were greatest in two species consistently acting as followers, Crested Drongo Dicrurus forficatus and Paradise Flycatcher Tersiphone mutata. Although as leaders, Newtonia Newtonia brunneicauda and Long-billed Greenbul Phyllastrephus madagascariensis often attracted other species, they also increased their Feeding rates through some mutualistic effects. Another leader, Rufous Vanga Shetba, rufa was the only species that neither changed foraging niche nor feeding efficiency in different social situations. Its participation in heterospecific associations probably resulted from other species exploiting the vanga's ability to detect predators. Therefore, the organization of multispecies flocks in Madagascar was mainly based on mutualism and commensalism which increased feeding efficiency.