Though I know this was questioned many moons ago, I recently came across the word to describe this phenomenon. It’s allelomimesis. From what I understand, new studies show that the most stable cluster sized is formed by a few individuals who are highly allelomimetic.
Welcome to the Straight Dope Message Boards, kerryraw, we’re glad you found us. For future ref, it’s helpful to other readers to provide a link to the column (or staff report) in question. Saves search time and tries to avoid duplication. No biggie, you’ll know for next time, and (as I say) welcome!
Link to Staff Report (from 2004): http://www.straightdope.com/columns/read/2151/how-does-a-flock-of-birds-wheel-and-swoop-in-unison
This was written by our resident ornithologist.
The short answer is that most lower animals and probably all life forms lower than that function more by algorithm than by anything like rational thought. While 100 humans might have a hell of a time doing instant simultaneous movements, you can devise a very simple algorithm that produces the behavior.
When I was in grammar school, we were told that birds have a tiny piece of lodestone in their heads and the minute magnetic fluctuations started by the lead bird caused them all to turn simultaneously. Sounds like magic; has this been rebuffed?
Birds can detect the magnetic field of the Earth, which is useful in long-distance navigation, but flocking behavior is based on reference to the two sides, which is where the eyes are. If you have ever had military training (even to the extent of being in a high-school marching band), you already know the basic secret—just keep the lines straight, and everything will work out.
just keep an even distance then you can do curves in three dimensions too.