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Re: evasive, camouflaged flocking



With regard to how flocking behavior affects predation.
I have spent some time observing flocks of prey birds interact
with predator birds (Hawks) near the Delaware Water Gap. Flocks not only

stay together under predator attack, they actively engage in cooperative

evasion, especially when the whole flock turns to present a different
aspect to the predator. Prey birds are often two-toned, with a light
belly and a dark topside. The classic explanation for this is that it
reduces visibility under ordinary topside illumination. However, the
dynamic
effects are much greater. The background for the flock is either light
grey (sometimes blue) sky or dark, irregular forest. When the flock
shifts
orientation it is very difficult to follow a single target against a
background
that closely matches the bird's tone. By shifting back and forth in tone
the
flock can make it very difficult for the predator to track a single
target
long enough to line up for a kill. Looking at the flock against sky and
grey winter forest I have seen it almost disappear in a flash.
Predators usually have to hit a single target to make a kill. By making
it
hard to track any member, a flock can increase the survivability
of all of its members.
I wonder if some prey dinosaurs had similar responses and coloration
that
made them disappear/reappear against the forest and hills.
-Gus Derkits


Bill Adlam wrote:

> Jaime wrote:
>
> >   As for reasons for flocking, could it be that
> > they're all prey birds?

>
> If predators are evenly distributed, you minimise your chances of
> meeting one by getting in between 2 or more other prey animals.  Of
> course, they're all trying to do the same...
>