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From local interactions to long-range correlations: an empirical investigation of collective behavior in starling flocks| old_uid | 6854 |
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| title | From local interactions to long-range correlations: an empirical investigation of collective behavior in starling flocks |
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| start_date | 2009/05/05 |
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| schedule | 12h15 |
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| online | no |
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| summary | Bird flocking is a striking example of animal collective behaviour:
thousands of birds gather above the roosting site, forming sharp-bordered flocks, which wheel and turn with remarkable coherence and synchronization.
Despite an increasing theoretical interest, empirical investigations of collective motion have been limited so far by the difficulties of getting data on large systems. By means of stereoscopic photography and using statistical mechanics, optimization theory and computer vision techniques, we have measured for the first time the three-dimensional positions, velocites and trajectories of individual birds in groups of up to four thousands elements.
This allowed us to characterize collective behaviour in great detail and to investigate the mechanismsleading to it. We found that the interaction between birds does not depend on their mutualmetric distance (how far apart they are), as most current models assume, but rather on the topological distance (number of intermediate neighbors). In fact, we discovered that each individualinteracts on average with a fixed number of neighbors (six-seven), irrespective of their distances incspace. We argue that a topological interaction of this kind is indispensable to maintain flock's cohesion against the large density changes caused by external perturbations, typically predation.
More recently, we characterized the velocity field, and computed dynamical correlation functions.
We showed that flocks exhibit long range correlations, which span the entire group and are a signature of their remarkable collective behavior. |
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| responsibles | Rampon, Giurfa |
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