Mutualism and Commensalism in Avian Mixed-Species Flocks in a Western Forest of Madagascar

Abstract

I examined the feeding rates and feeding niches of regular partcipating species of avian mixd-species flocks in a western forest of Madagascar in different social situations. The regular species were, Crested Drongo, Common Newtonia, Madagascar Paradise Flycatcher, Rufous Vanga, Blue Vanga, Long-billed Greenbul and Ashy Cuckoo Shrike. All of the species responded differently to mixed-flocking and thus it is suggested that the effects of association varied among species. The changing of feeding sites and/or technique was found in six species, five of which increased feeding rates. When participating in mixed flocks, they tended to use similar height and increased variations of location and/or technique. The interspecific convergence enhancing feeding rate, contrary to that expected from a competition may be explained from a social learning effect. The effect appeared to be greatest in Drongo, which increased feeding efficiency by changing not only foraging habits but also prey menu when foraging with other species. In Drongo, kleptoparasitism also appeared to contribut to increase feeding effisiency in mixed-flocks. Paradise Flycatcher also benefitted much from foraging in mixed flocks by a beating effect. The two species' consistently-following tactics in mixed-flocks is greatly paid through these effects. Although Newtonia and Greenbul often attracted other species as leaders, then, they increased feeding rates through some mutualistic effects. Rufous Vanga was the only species that changed neither feeding habits and feeding efficiency in different social situations. Most individuals of this species foraged in cohesive conspecific breeding groups, and frequently gave alarm calls and even direct attacks against predators. These characteristics of Rufous Vanga suggest that its conspecific groups moved independently of other species and that its association with heterospecifics probably resulted from other species following it to exploit its ability to detect predators.