energy-effective?

[B.Dol@skn.sc.philips.com]

Hello dino-experts,

I hope someone can answer a question which has been on my mind for a 
few days now. At this moment I'm reading 'Taking Wing' written by Pat 
Shipman (thanks for lending it to me, Ilja). 
By the way; so far this book is excellent reading even for a 
non-expert like me.
I've just finished the part about flying mechanics. 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? 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.
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?
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 hope someone (anyone) on this list can help me out on this. I would 
prefer the answer to be in simple language as I am not very familiar 
yet with the names of bones/muscles in birds (if they are needed to 
be included in the answer).
Thanks in advance for reading and/or trying to answer my question.

"Secrets must be exposed when found. 
Detours must be taken when encountered.
And if you are at the place of concealment or standing at the crossroads,
you must never leave it to another to act in your place."
Qui-Gon Jinn; Jedi Master