Group Mind in Flocks of Birds

The water pipits have just returned for their winter sojourn.  In the morning they often skim the water in flocks of 50 to a 100, turning this way, then that, seemingly as a whole.
Many times I’ve watched flocks of birds wheeling together, and wondered if this is truly a collective phenomenon, a consequence of some group mind, or whether some message passes through the flock too fast for me to notice. Water pipits provide an opportunity to consider this more closely. They are brownish on top, but pale underneath. When the flock turns it changes from brown to pale, or vice versa.
If the message to turn was propagating through the flock in some manner, then it would take a small, but finite, time to do so. I should be able to see this as a color change sweeping through the flock. Time and again, I have watched closely looking for such a change, but all I ever see is an instantaneous shift in color.
The flicker rate of the human eye (and brain) is around 1/20 sec. Events slower than this are seen as separate; faster and they appear at the same time. (Films and television present images faster than the flicker rate, so that you see the image moving smoothly.) So if there is any propagation of information through the flock, it must all take place in less than 1/20 sec, or else I’d see the change as a rapid sweep of color.
This doesn’t prove it is a collective phenomenon; it may be that information is propagated much faster than my eye can detect. It would be interesting to take a high speed film of them—at 100 frames/sec, or even 1000—and see if there is any shift across frames. If there is no discernable movement of the color change at that speed, we would have very good evidence for a group mind. (Anyone have a high-speed camera they want to loan me? )

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