Entropic effects in a nonequilibrium system: Flocks of birds

Michele Castellana, William Bialek, Andrea Cavagna, Irene Giardina

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


When European starlings come together to form a flock, the distribution of their individual velocities narrows around the mean velocity of the flock. We argue that, in a broad class of models for the joint distribution of positions and velocities, this narrowing generates an entropic effect that opposes the cohesion of the flock. The strength of this effect depends strongly on the nature of the interactions among birds: If birds are coupled to a fixed number of neighbors, the entropic forces are weak, while if they couple to all other birds within a fixed distance, the entropic effects are sufficient to tear a flock apart.

Original languageEnglish (US)
Article number052416
JournalPhysical Review E
Issue number5
StatePublished - May 23 2016

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Statistical and Nonlinear Physics
  • Statistics and Probability


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