We use the maximum entropy method to study how the strength of effective alignment between birds depends on distance. We find in all analyzed flocks that the interaction decays exponentially. Such short-range form is noteworthy, considering that the velocity correlation that is input of the calculation is long-ranged. We use our method to study the directional anisotropy in the alignment interaction and find that the interaction strength along the direction of motion is weaker than in the transverse direction, which may account for the anisotropic spatial distribution of birds observed in natural flocks.
Short-range interaction vs long-range correlation in bird flocks
Andrea Cavagna, Lorenzo Del Castello, Supravat Dey, Irene Giardina, Stefania Melillo, Leonardo Parisi, Massimiliano Viale