Andrea Cavagna
Centre for Statistical Mechanics and Complexity
INFM-CNR, Rome
Inferring the Inter-Individual Interaction Using Empirical Data in Collective Animal Behaviour: The
Case of Starlings
Bird flocking is a striking example of collective animal behaviour. A vivid illustration of such phenomenon is provided by the aerial display of vast flocks of starlings gathering at dusk over the roost and swirling with extraordinary spatial coherence. Both the evolutionary justification and the mechanistic laws of flocking are poorly understood, arguably because of the lack of empirical data on large flocks. Even though numerical models of collective animal behaviour are countless, in absence of large-scale reliable data in three dimensions it is hard to assess the validity of the models' assumptions and results. We report here a quantitative field study of flocking. By means of stereoscopic photography, computer vision and statistical mechanics we measured for the first time individual three-dimensional positions in compact flocks of up to several thousands birds in flight. Thanks to these data we were able to study the way birds interact with each other and to measure how the interaction decays with the inter-individual distance. Our results suggest that the nature of the interaction ruling collective animal behaviour is quite different from what was commonly assumed by most models and theories.