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During my usual weekend morning jaunt along Del Monte Beach in Monterey (California), I noticed for the first time the Plovers, who normally seem to forage nonstop, actually taking a communal break. About a dozen or so gathered together in a circle, and all but one or two bent their heads backwards and buried their faces in their "shoulder feathers."

They seemed to be just catnapping (the eyes slits, but not completely closed).

The one or two "sentinels" seemed to keep on eye on other critters getting too close (humans and dogs) and also on the surf. If something got too close, these sentinels somehow indicated this to their brethren. But how? If it was a sound, it may have been subsonic (at least, I didn't hear anything).

How do they say, "Wake up, peeps, and move over a bit!" And all moving together in the same direction at that?

What is their communication "secret"?

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    It depends. Was this in a location with good cell coverage? – Olin Lathrop Feb 15 '16 at 17:34
  • Good one; actually it is fair there; a little south in Big Sur, though, you're back in pre-cell days, so to speak. And perhaps it's no coincidence that I've never seen the Plovers communicating this way down in Garrapata. – B. Clay Shannon Feb 15 '16 at 17:38
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    I'm not sure if it's appropriate to stick in an unrelated comment, but I just came across a great organization called Mindful Birding, and they're very busy in the area in which you live. People like you and Liam, and other bird lovers (like @ab2), should check it out! – Sue Jun 29 '16 at 23:03
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    @Sue: Cool, thanks; also off topic, I saw 15 pelicans diving into the sea for dinner the other night (I'd seen one or two before, but never 15 in a short span of time). It was a virtual freeding frenzy. – B. Clay Shannon Jun 29 '16 at 23:06
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What your describing is flocking. It's an extremely complex behaviour where individuals react to their immediate neighbours giving the sense that the whole flock moves as a whole. Birds naturally flock (in the air or on the ground) as a defensive mechanism against predators, etc. Though complex there appears to be some basic rules to the mechanism as a whole:

Basic models of flocking behavior are controlled by three simple rules:

  • Separation - avoid crowding neighbors (short range repulsion)
  • Alignment - steer towards average heading of neighbors
  • Cohesion - steer towards average position of neighbors (long range attraction)

With these three simple rules, the flock moves in an extremely realistic way, creating complex motion and interaction that would be extremely hard to create otherwise.

Wikipedia

How flocking works isn't 100% understood yet, though computer simulations have been generated.


So in your example:

The "sentinals" would react to the perceived threat and move/react, their neighbours would react to this movement and then the following neighbours would then react, etc, etc until the whole flock reacted as a whole.

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    Like a cascade, one does it and it flows through to the others. – Aravona Feb 16 '16 at 10:50
  • Or like a jazz combo: one cat takes a side road, and the other cats go with him and then take their own little side road, etc. – B. Clay Shannon Feb 16 '16 at 15:38

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