Bird species are hypothesized to join mixed-species flocks (flocks hereon) either for direct foraging or anti-predation-related benefits. In this study, conducted in a tropical evergreen forest in the Western Ghats of India, we used intra-flock association patterns to generate a community-wide assessment of flocking benefits for different species. We assumed that individuals needed to be physically proximate to particular heterospecific individuals within flocks to obtain any direct foraging benefit (flushed prey, kleptoparasitism, copying foraging locations). Alternatively, for anti-predation benefits, physical proximity to particular heterospecifics is not required, i.e. just being in the flock vicinity can suffice. Therefore, we used choice of locations within flocks to infer whether individual species are obtaining direct foraging or anti-predation benefits. A small subset of the bird community (5/29 species), composed of all members of the sallying guild, showed non-random physical proximity to heterospecifics within flocks. All preferred associates were from non-sallying guilds, suggesting that the sallying species were likely obtaining direct foraging benefits either in the form of flushed or kleptoparasitized prey. The majority of the species (24/29) chose locations randomly with respect to heterospecifics within flocks and, thus, were likely obtaining antipredation benefits. In summary, our study indicates that direct foraging benefits are important for only a small proportion of species in flocks and that predation is likely to be the main driver of flocking for most participants. Our findings apart, our study provides methodological advances that might be useful in understanding asymmetric interactions in social groups of single and multiple species.
Species interactions Group-living Sociality Cooperation Grouping Anti-predator
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We thank the Ministry of Environment and Forests, Government of India and the International Foundation for Science (grant no. D/4910-1) for supporting this study and the Karnataka Forest Department for providing permits for field work. We thank Guy Beauchamp, Kavita Isvaran, and Maria Thaker for discussions regarding sampling design and analysis and comments on earlier manuscript drafts. HS thanks Prakash, Nagesh, Narayan, Chandrakant, and Sadanand for their help with field work.
This study complies with the current laws of India, where the study was carried out.
Conflict of interest
The authors declare that they have no conflict of interest.
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