Behavioral Ecology and Sociobiology

, Volume 67, Issue 2, pp 321–330 | Cite as

Social organisation of thornbill-dominated mixed-species flocks using social network analysis

  • Damien R. FarineEmail author
  • Peter J. Milburn
Original Paper


Mixed-species associations are a widespread phenomenon, comprising interacting heterospecific individuals which gain predator, foraging or social benefits. Avian flocks have traditionally been classified as monolithic species units, with species-wide functional roles, such as nuclear, active, passive, or follower. It has also been suggested that flocks are mutualistic interactions, where niches of participating species converge. However the species-level perspective has limited previous studies, because both interactions and benefits occur at the level of the individual. Social network analysis provides a set of tools for quantitative assessment of individual participation. We used mark-resighting methods to develop networks of nodes (colour-marked individuals) and edges (their interactions within flocks). We found that variation in flock participation across individuals within species, especially in the buff-rumped thornbill, encompassed virtually the entire range of variation across all individuals in the entire set of species. For example, female, but not male, buff-rumped thornbills had high network betweenness, indicating that they interact with multiple flocks, likely as part of a female-specific dispersal strategy. Finally, we provide new evidence that mixed-species flocking is mutualistic, by quantifying an active shift in individual foraging niches towards those of their individual associates, with implications for trade-off between costs and benefits to individuals derived from participating in mixed-species flocks. This study is, to our knowledge, the first instance of a heterospecific social network built on pairwise interactions.


Social network analysis Mixed-species flock Group living Foraging niche Individual variation 



We wish to thank the Australian Capital Territory Government and Mulligan’s Flat park rangers (P. Mills, G. Woodbridge, et al.) for providing access and continued support and the Fenner School for Environment and Society at the Australian National University for their collaboration. We thank Dr. Andrew Reeson, Dr. Louise Tierney and Lucy Aplin for their assistance, and Prof. Ben Sheldon, Dr. Colin Garroway, Dr. Eben Goodale and one anonymous reviewer for insightful comments. Funding assistance was provided by the European Research Council (AdG 250164) awarded to B. Sheldon, and Wolfson College Fieldwork Grant awarded to DRF.

Supplementary material

265_2012_1452_MOESM1_ESM.kml (206 kb)
Online Resource 1 KML polygons showing and interactive overview of the study that can be viewed using Google Earth™. 1. Catching sites: two polygons showing the habitat patches in which all individuals were captured. 2. Overall home-range: home-range calculated from the observed locations of each group combined. 3. Individual home-range: home-range of each individual coloured by species and individually selectable with details of home-range size. (KML 205 kb).


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Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  1. 1.Edward Grey Institute of Field Ornithology, Department of ZoologyUniversity of OxfordOxfordUK
  2. 2.College of Medicine, Biology & EnvironmentAustralian National UniversityCanberraAustralia

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