Re: Birds Fly Best on a Full Tank

["James R. Cunningham" <jrccea@bellsouth.net>]

The two primary points in this article seem to be that birds fly more
efficiently when heavily loaded and that there is an energy savings when
flying in a v-vormation, even when not positioned to take advantage of
the wake.  Neither of these effects should be unexpected.

For the first, increasing the wingloading (carrying a fuel load --
food), increases the airspeed without reducing the L/D ratio.  So a bird
that has recently fed will cover more ground per unit time than the same
bird when it is lighter, particularly when flying in a headwind.  Since
for a given bird, the wingbeat frequency increases with increasing
weight, and the power per unit mass of muscle increases with contraction
frequency, the combined effect should be an increase in overall
efficiency.  When flying into a headwind, there is even more improvement
than when flying downwind.   I don't see why this effect is unexpected,
and computer research does predict it.  The researchers appear to be
extremely competent, and I'm pretty sure they are aware of this.  Jeremy
is also extremely competent, and when he said that computers don't
predict it, I suspect he may have been speaking of specific types of
computer prediction, and may have been misquoted or quoted out of
context.  If you look at my posts in the archives, you will note that I
have been advocating the advantages of high wing loading for several
years, both in individuals and in species, with the caveat that for a
species optimal maximum wing loading will be limited by the particular
mechanisms that the specific species use as energy sources for their
particular type of flight.

For the second, flying in a v gives the trailing birds the opportunity
to observe the effects of gust transients on the birds in front of them,
thereby giving some warning and allowing them more time to adjust their
flight path to compensate to either take advantage of the transients or
minimise the detrimental effects, as appropriate.  This has nothing to
do with positioning in the wake.  Among other things, this will allow
the trailing animals to spend more time gliding or flying nearer their
best range airspeed.  This is similar to the reason that soaring birds
fly in patterns (not necessarily v's) that will let them observe the
effect of thermals or other uplift sources upon other birds in the
group, so that they spend relatively less time searching for lift and
more time traveling between cells.

That said, this appears to be really good work, and I look forward to
reading it.

All the best,

Jim

P.S.  Knots are pretty birds.

Danvarner@aol.com wrote:

>        Here's a very interesting story from Nature. DV
>
>        http://www.nature.com/nsu/011018/011018-10.html