Three-dimensional reconstruction of starlings in flight: an experimental investigation of collective behaviour
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)Abstract
Bird flocking is a striking example of collective 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 data on large flocks. We report here a quantitative study of aerial display. By means of stereoscopic photography, statistical mechanics, optimization theory and computer vision techniques, we measured for the first time individual three-dimensional positions in compact flocks of up to several thousands birds. This allowed us to analyze global morphological properties (shape of the flock, orientation with respect to gravity, turning manouvres), as well as structural properties (anisotropic distribution of neighbours, hard-core repulsion). Most notably, we investigated whether or not the physical distance among birds is the natural scale for the spatial organization of the individuals within the flock. Our findings have some interesting implications on the nature of birds interaction. These quantitative results can be compared to other species (fish schools, mammals herds), and more generally to numerical models of animal collective behaviour.