Shortrange interactions versus longrange correlations in bird flocks
Abstract
Bird flocks are a paradigmatic example of collective motion. One of the prominent traits of flocking is the presence of long range velocity correlations between individuals, which allow them to influence each other over the large scales, keeping a high level of group coordination. A crucial question is to understand what is the mutual interaction between birds generating such nontrivial correlations. Here we use the maximum entropy (ME) approach to infer from experimental data of natural flocks the effective interactions between individuals. Compared to previous studies, we make a significant step forward as we retrieve the full functional dependence of the interaction on distance, and find that it decays exponentially over a range of a few individuals. The fact that ME gives a shortrange interaction even though its experimental input is the longrange correlation function, shows that the method is able to discriminate the relevant information encoded in such correlations and single out a minimal number of effective parameters. Finally, we show how the method can be used to capture the degree of anisotropy of mutual interactions.
 Publication:

Physical Review E
 Pub Date:
 July 2015
 DOI:
 10.1103/PhysRevE.92.012705
 arXiv:
 arXiv:1407.6887
 Bibcode:
 2015PhRvE..92a2705C
 Keywords:

 87.23.Cc;
 05.65.+b;
 87.10.e;
 89.70.Cf;
 Population dynamics and ecological pattern formation;
 Selforganized systems;
 General theory and mathematical aspects;
 Entropy and other measures of information;
 Physics  Biological Physics;
 Condensed Matter  Statistical Mechanics;
 Quantitative Biology  Populations and Evolution
 EPrint:
 21 pages, 7 figures, 1 table