Istituto Sistemi Complessi, Consiglio Nazionale delle Ricerche, UOS Sapienza, 00185, Rome, Italy.
Dipartimento di Fisica, Università Sapienza, 00185, Rome, Italy.
Nat Commun. 2022 May 10;13(1):2315. doi: 10.1038/s41467-022-29883-4.
Speed fluctuations of individual birds in natural flocks are moderate, due to the aerodynamic and biomechanical constraints of flight. Yet the spatial correlations of such fluctuations are scale-free, namely they have a range as wide as the entire group, a property linked to the capacity of the system to collectively respond to external perturbations. Scale-free correlations and moderate fluctuations set conflicting constraints on the mechanism controlling the speed of each agent, as the factors boosting correlation amplify fluctuations, and vice versa. Here, using a statistical field theory approach, we suggest that a marginal speed confinement that ignores small deviations from the natural reference value while ferociously suppressing larger speed fluctuations, is able to reconcile scale-free correlations with biologically acceptable group's speed. We validate our theoretical predictions by comparing them with field experimental data on starling flocks with group sizes spanning an unprecedented interval of over two orders of magnitude.
由于飞行的空气动力学和生物力学限制，个体鸟类在自然群体中的速度波动适中。然而，这种波动的空间相关性是无标度的，也就是说，它们的范围与整个群体一样广泛，这一特性与系统集体对外界干扰做出反应的能力有关。无标度相关性和适度波动对控制每个个体速度的机制提出了相互冲突的限制，因为增强相关性的因素会放大波动，反之亦然。在这里，我们使用统计场论方法，提出一种边缘速度限制，它忽略了自然参考值的小偏差，同时强烈抑制较大的速度波动，从而能够协调无标度相关性和生物学上可接受的群体速度。我们通过将理论预测与跨越两个数量级以上的前所未有的星鸦群体大小的现场实验数据进行比较，验证了我们的理论预测。
