A dancing flock of starlings hypnotize us like the fire. The flock fly as a single bird; contracting and expanding, going up and then down into the trees of the avenue. The flock is clearly more than the messy sum of some hundreds of birds: it is a self-organized dynamic system showing emergent properties that escape to our comprehension.
This is why science exists, to explain the magic trick, and enjoy nature with renewed eyes. We know from a long time ago that in a flock of starlings there isn’t a single leader governing the dance: a flock is a decentralized system where the cohesion and movement of the group is created by the massive interaction among birds.
Italian researchers have gone a step further in this explanation by taking many pictures from starling flocks flying over the city of Rome. Then, they reconstructed on the computer the 3D position of each individual inside the flock, and studied how the flight of a given bird was shaped by its neighbors. They discovered that birds aren’t affected by the position of all neighbors within a certain distance (lineal distance), but only by those six closest neighbors (topographic distance). Implementing this rule as an algorithm into a simulation model, they showed that this individual behavior enhanced the compactness of flocks when attacked by a predator. In this way, starlings evade the attack of the falcon, leaving him hypnotized by their self-organized magic.
> M. Ballerini, et al. (2008) Interaction ruling animal collective behavior depends on topological rather than metric distance: Evidence from a field study. PNAS 105: 1232-1237. (Open Access)
> M. Resnick (1994) Turtles, Termites, and Traffic Jams. Explorations in Massively Parallel Microworlds. (see an interesting introduction to decentralized systems in this book)
Photo by "He and Fi" (Flickr; Creative Commons)
This post was previously published in Catalan and Spanish in this blog (see here)
Ballerini, M., Cabibbo, N., Candelier, R., Cavagna, A., Cisbani, E., Giardina, I., Lecomte, V., Orlandi, A., Parisi, G., Procaccini, A., Viale, M., & Zdravkovic, V. (2008). From the Cover: Interaction ruling animal collective behavior depends on topological rather than metric distance: Evidence from a field study Proceedings of the National Academy of Sciences, 105 (4), 1232-1237 DOI: 10.1073/pnas.0711437105