Not one starling in that shape-shifting cloud knows what the flock looks like. Each bird reads only a handful of neighbours, then does three things: veer off when crowded, turn toward the average heading of the group, drift back toward its centre. Craig Reynolds wrote those three rules in 1986, and the order of the whole flock condenses into a single number, the length of the mean heading vector: migrating birds push it close to 1, while an insect swarm all but abandons alignment and lets it fall to 0. Send a hawk through and the 280 birds split, swirl around the hunter and close up again.
Not one starling in that shape-shifting cloud knows what the flock looks like. Each bird reads only a handful of neighbours, then does three things: veer off when crowded, turn toward the average heading of the group, drift back toward its centre. Craig Reynolds wrote those three rules in 1986, and the order of the whole flock condenses into a single number, the length of the mean heading vector: migrating birds push it close to 1, while an insect swarm all but abandons alignment and lets it fall to 0. Send a hawk through and the 280 birds split, swirl around the hunter and close up again.
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