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Re: energy-effective?

B.Dol@skn.sc.philips.com wrote:

> If I understood correctly (I hope) the furcula and sternum are somewhat 
> flexible in
> birds.
> Does this improve the energy-effectiveness of flight in birds?


> As I see it the
> recoil (coming from the flexibility) could lessen the energy the bird has to
> spend in the next movement (being it up- or downstroke). Or is just as much
> energy spent on building up the tension in the bone?

Yes to the latter, if you replace the word 'tension' with 'stress and strain' 
and the word
'bone' with 'bone/tendon/ligament complex'.  The advantage to the animal is 
that it allows
the timing of the energy transferred to the atmosphere to be adjusted, and that 
it reduces
the peak forces involved in the flight stroke. It allows the animal to spread 
the muscle work
over a longer time period, reducing peak loads, and allows the animal to fly 
with a slightly
smaller muscle mass than would otherwise be required.

> Maybe the answers are
> somewhere in the text (than I'm sorry I've missed it/didn't
> understand it) or in the chapters yet to come.

I haven't read the book yet.  Do you recommend it?

> It this kind of flexibility normal in bones from birds? Is this a
> characteristic which leaves evidence in fossils; what I mean is this:
> can one looking at the bones of a archaeopteryx see that the bones
> were flexible in life and how?

It is possible to tell this in pterosaurs (in some circumstances, and in a 
limited way).  I
would expect the same in birds, but have not investigated that in any way.  Ken 
Dial has done
strain gage work on the humerus of flying pigeons that might address your 

> I just thought about it this weekend and 'build' a very experimental 
> recoiling cage
> with sticks and elastic material and it seemed to be very easy to keep the 
> movement
> going once it had started (equivalent for a prolonged flight). For only a few 
> 'flaps' (or
> the equivalent of a short flight) it seemed a bit more difficult (and thus 
> less
> energy-effective) to me.

I think you may well be right here.  For a short flight, I would expect a bird 
to use more
anaerobic muscles, and I would expect him to press a larger fraction of muscle 
fiber into
short term use.  I would also expect any elastic energy storage mechanism to 
have a natural
resonance frequency.  Since animals commonly beat at a slightly higher 
frequency on takeoff
and on landing, I would expect any storage system to function effectively 
either in cruise or
on takeoff or landing, but not all three.