Re: Great in the air, not so good underwater

[Michael Habib <mhabib5@jhmi.edu>]

> > So, for example, large seabirds are loading limited to the extent 
> > that they have to be able to hit steady state from a running start 
> > and they can only run so fast.
>
> No, they don't have to be able to hit steady state directly from a 
> running start.  All they have to hit is an anaerobic burst window, and 
> have the ability to accelerate to steady state before the burst power 
> runs out.

Point taken.  Just the same, the running launch system has particular 
constraints and benefits.  I should have said "to reach their burst 
window" rather than "to hit steady state".

> And swans use a very different technique that involves (in visual 
> extreme --  for purposes of qualitative illustration) a 
> 'hovercrafting' technque combined with 'jet thrust augmentation' 
> during a portion of the flapping cycle...

Yeah, swan takeoffs just blow my mind.  Cool stuff.  I was mostly 
referring to sulids and procellariiforms
when I mentioned running starts in seabirds before.  I probably should 
have been more specific.  Grebes and loons also use running starts, but 
those are different, as well.

> However, my real point is that if flight is truly important to the 
> animal, it or its decendants will partially sidestep the launch issue. 
>  A couple of ways to accomplish this are cliff launching and front 
> limb assist during launching (I'm not sure how a bird would accomplish 
> that latter, but bats and pterosaurs can).  Given enough time for 
> evolution to operate, I suspect there are hundreds of other ways as 
> well.

I'm sure there are very many indeed.  What launch modes are open seems 
to basically depend on the old standbys of historical constraint and 
selection.  Constraint pretty clearly prohibits the forelimb-assisted 
launch cycle in birds, and thus I doubt they'll ever produce volant 
members as large as pterosaurs.  Stabilizing selection is probably hard 
at work, too, though: despite denying some helpful launch modes, avian 
bipedality has some great advantages.  In fact, being bipedal gives 
birds access to some launch solutions denied to pterosaurs and bats; 
the ones I have in mind work best at small to medium body sizes.

Still, I'll bet nothing beat seeing a Quetzalcoatlus catapault off the 
ground...makes me sad that they're gone.

Cheers,

--MH