Starling Flocks: Union is Strength

How can they do this? What is the key of their amazing cohesion? This is one of the questions the STARFLAG project – Starlings in Flight – aims to answer. The project, which started in 2005, is an EC-funded collaboration of seven European institutes, coordinated by the Italian National Institute for the Physics of Matter (INFM-CNR). Physicist Giorgio Parisi is the head of this European network.

The prominent task of STARFLAG was to collect empirical data on large flocks of starlings in the field, and to test the predictions of former theories. The equipe headed by INFM-CNR researcher Andrea Cavagna, conducted experiments over the skies of Rome and discovered that the behaviour of flocking birds is very different from what believed up to now. Current computer models assume that each bird interacts with all birds within a certain physical distance. Empirical observations, however, show that each bird keeps under control a fixed number of neighbours (seven), irrespective of their physical distance. A flock under predator attack may expands dramatically, but birds can regroup very quickly because the cohesion does not depend on the physical distance among starlings, but rather on their ability to interact with a fixed number of neighbours.

The INFM-CNR results will be published today in the Proceedings of the National Academy of Sciences.

To obtain these empirical results the INFM-CNR equipe employed a multidisciplinary approach, using tools from stereometry, statistical physics and computer vision. The 3D position of individual birds has been reconstructed within flocks of thousands of starlings in the field. “Up to now numerical models of flocking had never been tested against empirical data, and it was impossible to select the right model. Now, thanks our data, we can really measure what goes on within a flock”, says Andrea Cavagna. “An interaction based upon the number of neighbours rather than their distance, implies rather complex cognitive capabilities in birds”- adds Irene Giardina, another INFM-CNR researcher.

According to Andrea Cavagna, “the STARFLAG findings may be important for fields as mobile robotics and control theory, where highly coordinated swarms of simple agents must solve complex tasks through a bottom-up approach.”