How do Plover sentinels give the "move out" signal?
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"?
This post was sourced from https://outdoors.stackexchange.com/q/10921. It is licensed under CC BY-SA 3.0.
1 answer
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.
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.
This post was sourced from https://outdoors.stackexchange.com/a/10924. It is licensed under CC BY-SA 3.0.
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