Local equilibrium in bird flocks

Thierry Mora, Aleksandra M. Walczak, Lorenzo Del Castello, Francesco Ginelli, Stefania Melillo, Leonardo Parisi, Massimiliano Viale, Andrea Cavagna, Irene Giardina

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Abstract

The correlated motion of large bird flocks is an instance of self-organization where global order emerges from local interactions. Despite the analogy with ferromagnetic systems, a major difference is that flocks are active – animals move relative to each other, thereby dynamically rearranging their interaction network. Although the theoretical importance of this off equilibrium ingredient has long been appreciated, its relevance to actual biological flocks remains unexplored. Here we introduce a novel dynamical inference technique based on the principle of maximum entropy, which takes into account network reshuffling and overcomes the limitations of slow experimental sampling rates. We apply this method to three dimensional data of large natural flocks of starlings, inferring independently the strength of the social alignment forces, the range of these forces, and the noise. We show that the inferred timescale of bird alignment is much smaller than the timescale governing the rearrangement of the interaction network. We verify that, following from this observation, an equilibrium inference method assuming a fixed interaction network gives results that are fully consistent with the dynamical inference. We conclude that the birds’ flight orientations are in a state of local equilibrium.
Original languageEnglish
Pages (from-to)1153-1158
Number of pages6
JournalNature Physics
Volume12
Early online date15 Aug 2016
DOIs
Publication statusPublished - 1 Dec 2016

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birds
inference
alignment
interactions
ingredients
animals
sampling
flight
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Mora, T., Walczak, A. M., Del Castello, L., Ginelli, F., Melillo, S., Parisi, L., ... Giardina, I. (2016). Local equilibrium in bird flocks. Nature Physics, 12, 1153-1158. https://doi.org/10.1038/nphys3846

Local equilibrium in bird flocks. / Mora, Thierry; Walczak, Aleksandra M.; Del Castello, Lorenzo; Ginelli, Francesco; Melillo, Stefania; Parisi, Leonardo ; Viale, Massimiliano ; Cavagna, Andrea; Giardina, Irene.

In: Nature Physics, Vol. 12, 01.12.2016, p. 1153-1158.

Research output: Contribution to journalArticle

Mora, T, Walczak, AM, Del Castello, L, Ginelli, F, Melillo, S, Parisi, L, Viale, M, Cavagna, A & Giardina, I 2016, 'Local equilibrium in bird flocks', Nature Physics, vol. 12, pp. 1153-1158. https://doi.org/10.1038/nphys3846
Mora T, Walczak AM, Del Castello L, Ginelli F, Melillo S, Parisi L et al. Local equilibrium in bird flocks. Nature Physics. 2016 Dec 1;12:1153-1158. https://doi.org/10.1038/nphys3846
Mora, Thierry ; Walczak, Aleksandra M. ; Del Castello, Lorenzo ; Ginelli, Francesco ; Melillo, Stefania ; Parisi, Leonardo ; Viale, Massimiliano ; Cavagna, Andrea ; Giardina, Irene. / Local equilibrium in bird flocks. In: Nature Physics. 2016 ; Vol. 12. pp. 1153-1158.
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