Scale-free correlations in starling flocks

Raffaele Santagati

Research output: Contribution to journalArticle (Academic Journal)peer-review

467 Citations (Scopus)

Abstract

From bird flocks to fish schools, animal groups often seem to react to environmental perturbations as if of one mind. Most studies in collective animal behavior have aimed to understand how a globally ordered state may emerge from simple behavioral rules. Less effort has been devoted to understanding the origin of collective response, namely the way the group as a whole reacts to its environment. Yet, in the presence of strong predatory pressure on the group, collective response may yield a significant adaptive advantage. Here we suggest that collective response in animal groups may be achieved through scale-free behavioral correlations. By reconstructing the 3D position and velocity of individual birds in large flocks of starlings, we measured to what extent the velocity fluctuations of different birds are correlated to each other. We found that the range of such spatial correlation does not have a constant value, but it scales with the linear size of the flock. This result indicates that behavioral correlations are scale free: The change in the behavioral state of one animal affects and is affected by that of all other animals in the group, no matter how large the group is. Scale-free correlations provide each animal with an effective perception range much larger than the direct interindividual interaction range, thus enhancing global response to perturbations. Our results suggest that flocks behave as critical systems, poised to respond maximally to environmental perturbations.
Original languageEnglish
Pages (from-to) 11865–11870
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume107
Issue number26
DOIs
Publication statusPublished - 11 May 2010

Keywords

  • Collective behaviour
  • complex systems
  • ANIMAL BEHAVIOR

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