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Re: flocking






> Jim C wrote, in part:
>
> Consequently, all the birds' airspeeds will gradually tend to increase
> during the
> course of a flight.<

Norton, Patrick wrote:

> but metabolizing muscle would reduce power, and
> it's difficult to see how reduced power could translate into increased
> airspeed. Perhaps adjustments in the arrangement of the flock relate to
> averaging out increased speed during the first phase (fat burning) and
> decreased average speed during the later (muscle metabolizing) phase.

Reduced mass with a constant wingspan results in reduced induced drag for a
given airspeed, and consequently reduced power required (and muscle mass
required) for any given airspeed.  This is a well-known, well documented
aspect of long-distance bird migration.  As a somewhat related example, JAP
(the largest Whooper swan on record) achieved his lifetime highest recorded
airspeed during the last four hours of a flight from Scotland to Iceland in
an attempt to avoid being blown west past the southwest coast of Iceland
during prolonged galeforce winds.  During those last four hours, his average
airspeed was considerably faster than the best instantaneous speed he was
capable of achieving at his greater mass upon start of the flight.  It has
been estimated that he was within an hour or two of totally depleting his
fuel reserve when he finally made landfall.  Due to his large size, JAP is
not the fastest recorded Whooper.  That honor belongs to a smaller female.  I
would place JAP's desperation flight among the most impressive ever made,
matching many human accomplishments.  Colin Pennycuick did an excellent
documentation of the flight in one of his papers on Whoopers.  I think it was
in J. Exp. Biol., but don't have it in front of me right now.  Can look it up
if anyone wishes.

Don't expect airspeed to decrease when muscle is being metabolized.  For some
individuals -- sometimes -- it may.  But don't expect it.

JimC