Changes to the flight course of a flock of starlings can be described using a linear dispersion model, where information about the altered direction of the first bird propagates to others in a bird-to-bird transfer of information. These results, reported this week in Nature Physics, reveal the underlying mathematical similarities between collective motion in bird flocks and quantum phenomena in bulk systems.
Around sunset, starlings fly in tight formations of a few hundred to tens of thousands, and sometimes up to millions, of individuals. How they manage to move coherently without colliding or breaking up the formation has been debated. One presently supported model states that bird flight is a collective motion, with no particular leader, in which information is diffusively transported between birds.
Asja Jelic and colleagues filmed a flock of 400 starlings in the wild using three cameras, enabling them to track the individual trajectory of each bird in three-dimensions. Their findings conflict with the collective motion model: they found that a few ‘top birds’ change direction first, and that they are positioned near to each other within the formation. The directional information subsequently reaches all the members within roughly half a second. Thus, the rapid information transfer is not diffusive, but rather the collective behaviour can be described using the language of phase transitions and symmetry breaking characteristic of quantum matter.