I am a glider pilot and consequently have great admiration of bird flight, and
in
particular, soaring flight.
It is the energy aspects of soaring flight which intrigue me most. While I
have no
measurements to support my ideas, it seems that soaring birds use very little
energy
diring soaring flight. It may be cosidered that, compared with flapped flight,
soaring flight saves energy roughly in the ratio of the bird's glide ratio ie
about
12:1. Even this does not seem to quite fit in with the time soaring birds
spend in
what appears to be flight for flight's sake. Recently we were on Mt Gower on
Lord
Howe Island and saw the Providence Petrels spending what appeared to be most of
the
day soaring over the saddle between the two mountains. Likewise I have met
wedge-tailed eagles at over 9,000 feet. They may have been marking their
territory,
or they may have been there to get cool - it was on hot days - but in either
case it
would take a considerable amount of energy if there are no energy saving
features in
the eagle's physiology.
It would seem to me that if soaring birds have to hang on their pectoral
muscles they
would not have such a great saving over flapping birds unless there were
physiological differences. These differences may be:
1) some means of locking their "shoulders" so that the weight was not
carried on
the pectoral muscles (cf. our knees, horses rear legs etc);
2) the pectoral muscles fully extended when in soaring position so that
energy
was not needed to maintain that position;
3) different muscle type in the pectoral muscles adapted for continuous
load in
soaring birds;
4) some other way of breathing - I understand the act of flapping moves
air in
and out of the bird's lungs;
5) some other way of moving blood through the pectoral muscle tissue -
soaring
birds would not have the flapped flight expansion/contraction cycles which move
blood.
The other line of reasoning is that in nature, if an efficiency can be made, it
is
usually found somewhere. Therefore I would expect some soaring birds to show
some
specialisation which maximises the efficiency of soaring flight.
I would be most interested to receive any suggestions which may satisfy my
curiosity.
Thanks,
John Anselmi
Email:
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