Effect of species richness and composition on foraging niches in mixed species bird flocks

Abstract

Facilitative relationships and non-trophic interactions are important contributors to determining the ecological niche of an organism. One such non-trophic interaction occurs in mixed-species bird flocks (flocks, hereafter). Flocks are examples where a niche of an individual bird is potentially modified by the presence of other species while foraging. The niche of an organism has been defined as ‘a multi-dimensional hyper volume’ of many variables. This aspect of the ecology of mixed-species flocks – namely their niches– remains under-studied. I studied mixed-species bird flocks in the semi-evergreen forests of Anshi National Park in the Western Ghats of India to understand the effect of richness and composition of the flock on the foraging niches of individual participants. I sampled a total of 113 flocks during the months January 2020 - March 2020. I used foraging height and behavior as representatives of the foraging niche which are the most relevant in the flock context. Foraging height ranges were correlated with species richness whereas average flocking heights were not. The results suggest that two of the nuclear gregarious species – which are key to flock formation and maintenance - are likely to determine the height of flock. Further, these gregarious species may influence the height of two other important sallying species that often follow the flock nucleus. Overall, this study contributes to the understanding of the foraging niche modifications that act on an individual level while influencing interactions at the group level in flocks.