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Lay Summary

Posted by Hemelrijk on 05 Aug 2011 at 07:49 GMT

Some causes of the variable shape of flocks of birds

Charlotte K. Hemelrijk*, Hanno Hildenbrandt

Behavioural Ecology and Self-organisation, Centre for Ecological and Evolutionary Studies, University of Groningen, Groningen, The Netherlands
Author summary
Both scientists and laymen have wondered for ages about the apparent ease with which moving groups of animals coordinate and ‘decide’ on group-shape. The shape of flocks of birds shows great variability. One of the most spectacular examples of it is seen during aerial manoeuvers of starlings when they are flying in flocks of tens of thousands above their sleeping site at dawn. It is very difficult to study causes of flock-shape in nature. Since in an earlier study we have shown that a computer model, StarDisplay, produces flocking patterns that closely resemble empirical data, we now use this model to investigate the causation of flock shape. Individuals coordinate with a few others closeby, while their flying behaviour is represented by simplified aerodynamics. The shape of the flock emerges automatically by self-organisation. Experiments in our model show that the variability of flock shape is due to two traits specific to flying behavior: rolling while turning and (almost) fixed speed during turning. Further, variability of shape increased when in general the variability of behavior in the flock is larger, with one exception, which concerns the low variability of speed. Thus, flock-shape is more variable when flocks are larger, when individuals mind fewer neighbours, when individuals turn rather than fly in a straight line forward, and when they turn by a rolling-movement rather than without it, but, unexpectedly, also when variability of speed is low (rather than high). Predictions of our model should subsequently be tested empirically.

No competing interests declared.