[Tweeters] Motion in Birds

[Robert O'Brien via Tweeters]

Thanks to Mark for that fascinating explanation of head (non) motion.  I
have another question for him that may OR MAY NOT be apropos.
In recent years there have been discussions about how flocks of various
birds (starlings, sandpipers, etc.)  manage their motions in formation.
I recall one study a few years back that determined that Starlings manage
to do their maneuvers so that each one was surrounded by 6 other Starlings.
I'm a chemist so I recognize that 'structure' as hexagonal close-packing.
That is, if you have objects (marbles, golf balls, molecules, etc) all
the same size then they have
the highest density if each object is surrounded by 6 others.
(This gets into crystalline structure such that all sorts of other
structures are possible, especially if objects are of different sizes.
Sodium chloride (table salt) has a cubic structure due to the difference in
size between the small positive Sodium (+) ion and the larger negative
Chloride (-) ion.).  Etc.

But chemistry aside, in flight all the Starlings are moving, but the 6
birds around each (except for their joint directed motion) are basically
stationary.  And then?   Some bird(s) change direction, which is echoed at
a delayed time by the entire flock.   This is often stated to be a means of
avoiding predators (hawks)  but I believe Starlings do that even when no
predators are present.  Maybe just for fun?.  (Turkey Vultures seem to sail
around for extended periods, no synchrony, just for fun).

Any comments on this Mark?  Thanks

Bob OBrien   Portland

P.S.   I won't bother to dig out photos, but I have noticed that
Sanderlings running on the beach back and forth with the waves, often also
run in formation, so that all their legs in a photograph are in sync with
each other.    And speaking of the beach, there are fish schools that
behave like Starlings, etc. etc.  Finis!
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