Nice article. It's not surprising to find the density increases at the edge if you factor in the fact that any bird finding itself on the outside will have a stronger need to get back into the midst of the flock for safety. In the center, drifting in any direction has no additional risk, but drifting the wrong way on the edges is something a bird (or boid) would need to correct quickly. The rule would be "move strongly away from clearly empty areas".
Also, has there been any work to correlate these three-dimensional behaviors with the behavior of herd animals? The flattening of flocks could be taken to 2-D if herds are substituted for flocks. They would have the same tendency to stay within the herd, and to do so more strongly when near the edge (and potential predators). Think circle of musk oxen, (or the typical movie scramble to NOT be in the front when the sergeant shouts for volunteers to take one step forward).
I wish I could suggest a herd-based version of "boid" but nothing fun enough comes to mind right now!
posted by Brian Fagan
December 22, 2010
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