In both single- and mixed-species social groups, certain participants are known to play important roles in providing benefits. Identifying these participants is critical for understanding group dynamics, but is often difficult with large roving social groups in the wild. Here, we develop a new approach to characterize roles in social groups and apply it to mixed-species bird flocks (flocks hereafter) in an Indian tropical evergreen forest. Two types of species, namely intraspecifically gregarious and sallying species, are thought to play important roles in flocks because studies have shown they attract other flock participants. However, it is unclear why these types are attractive and whether they are essential for flock formation. We address these questions by focusing on the composition of the subset of flocks containing only two species each. In two-species flocks, it is reasonable to assume that at least one species obtains some kind of benefit. Therefore, only those species combinations that result in benefit to at least one species should occur as two-species flocks. Using data from 540 flocks overall, of which 158 were two-species flocks, we find that intraspecifically gregarious species are disproportionately represented in two-species flocks and always lead flocks when present, and that flocks containing them are joined significantly more by other species. Our results suggest that intraspecifically gregarious species are likely to be the primary benefit providers in flocks and are important for tropical flock formation. Our study also provides a new approach to understanding importance in other mixed-species and single-species social groups.
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We thank the Ministry of Environment and Forests, Government of India and 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 Eben Goodale, Rajah Jayapal and Kathryn Sieving for commenting on a draft of this paper. H.S. thanks Prakash, Nagesh, Narayan, Chandrakant and Sadanand for help with fieldwork. This paper was completed when H.S. was a fellow of the Wissenschaftskolleg zu Berlin.
Conflict of interest
The authors declare that they have no conflict of interest.
This study complies with the current laws of India, where the study was carried out.
Communicated by Toni Laaksonen.
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Sridhar, H., Shanker, K. Importance of intraspecifically gregarious species in a tropical bird community. Oecologia 176, 763–770 (2014). https://doi.org/10.1007/s00442-014-3045-0
- Animal sociality
- Mixed-species flocks
- Species importance