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Re: evasive, camouflaged flocking



Gus Derkins wrote:

> 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...

True, and the same goes for many fish.  However, solitary animals
(both predators and prey) are also usually countershaded.  So the
issue is whether there is any consistent difference between solitary
and gregarious animals.

I would guess it's better for flocking birds to have large patches of
colour that confuse predators as you described.  Crypsis against the
ground or sky would take second place.  However, a change in pattern
couldn't evolve very fast, because any bird noticeably different to
the others would become an easy target to track.

As for dinosaurs, many were the size of elephants or bison or
wildebeest, all of which have comparatively uniform coloration.  I
think the largest herd animals (on land) with a disruptive colour
scheme are zebras.  Excluding domesticated cattle, of course.

Bill Adlam
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