Re: Campbell's even crazier than a MANIAC? (archeopteryx

[Michael Habib <mhabib5@jhmi.edu>]

> On the subject of leaping launches, here is an excellent slow mo video  
> of a seagul doing so (among other things)
> http://uk.youtube.com/watch?v=gAtIIlEVTok&eurl=http://people.eku.edu/ 
> ritchisong/554notes3.html

Nice vid :)

> I'll note that the leap coincides with a wing beat, and is into the  
> wind.

Actually, it coincides with the upstroke - the downstroke comes just as  
the initial impulse finishes.  The gust might be helping, but isn't  
required.

> Not all birds will leap into the air, quite a few take running starts,  
> or will do so if they do not have the aid of wind.

True, but those that use running launches are mostly adapted to  
semi-aquatic ecologies.  It mostly shows up as an adaptation to deal  
with launching from compliant surfaces, not a power reduction strategy.

> A hummingbird need not leap or run, the wing beat alone is powerful  
> enough.

Actually, 59% of the initial impulse during launch comes from the  
hindlimb in hummingbirds (Tobalske, 2004).  That said, they should be  
able to manage a launch with much less hindlimb impulse given their  
particular wing kinematic and launch regime.

> When discussing current "leap launching" birds which have very well  
> developed flight muscles and strokes, I think it might be an error to  
> attribute the leap launch ability to birds inheriting highly powerful  
> hindlimbs from their ancestors.

Perhaps, but in modern birds that use a leaping launch (most of them)  
80-90% of the initial force comes from the hindlimb.  Therefore, the  
well developed flight muscles and flight stroke have less of an impact  
in that regard than it seems.  The major impact, with with regards to  
launch, is in burst ability - many modern birds can launch at steep  
angles and very high initial climb accelerations (immediately after  
leaving the ground) and that requires a highly derived flight apparatus  
(and substantial anaerobic capacity).

> A primarily cursorial bird like a wild turkey probably has hindlimbs  
> more akin to the ancestral coelosaur than a seagul, the turkey's legs  
> certainly have proportionally more muscle mass than those of a seagul  
> - yet its launch style is most often (personal observation, not  
> neccesarily factual) a running launch.

Actually, turkeys are known to be highly specialized burst launchers.   
They can launch nearly vertically at very high rates, from a  
standstill.  I have observed the same thing as you, but it's deceiving  
- turkeys prefer to run from danger, when possible, so they tend to run  
first, and then launch when they recognize that it's required.  It's  
not actually a true running launch.  Askew has done a lot of nice work  
on launching in turkeys and pheasants.  Tobalske did some as well, I  
believe.

> I would suggest a no wind leaping launch on flat ground is technically  
> more demanding (from an engineering point of view) than a running one,  
> and requires a well developed flapping mechanism, or very well  
> developed leaping mechanism to work.

It's not clear that a leaping launch is actually more demanding (which  
I take to mean higher power requirements).  Running launches are  
derived within modern birds, and are usually associated with long span,  
high wing loading, short, stout hindlimbs, and launching from compliant  
surfaces.  All of these are associated with launching from water.   
There are some exceptions to the overall pattern - flamingos running  
launch over water surfaces, having stout enough femora to manage the  
loads, and webbed feet to help with the water launch.  The distal lower  
limb is also stronger in flamingos than it might appear, so they don't  
buck the trend too heavily.  In any case, running launch is not  
associated with lower power availability.

> A running start just requires clearance for the wings, which need to  
> have sufficient efficiency and surface area to have a stall speed  
> lower than the animals top running speed. Then even weak flapping  
> should be sufficient.

But running launchers are generating a great deal of the launch force  
from the hindlimbs, just as leaping launchers are.  In fact, the wings  
are mostly engaged to pull the animal up onto the water so that the  
legs can push against the surface.  In albatrosses, for example, the  
hindlimbs are stronger than the forelimbs.  Also, wing clearance is  
greater in a leaping launch than a running one.  For most birds, the  
leaping velocity is close to the stall speed, in any case.

> Lacking well developed flight muscles, in my opinion, an exceptional  
> leaping aparatus is needed, but only a mediocre running aparatus.

I don't think this is correct - both running and leaping launches  
generate the major portion of launch force and speed from the  
hindlimbs, so the lack of pectoral girdle power shouldn't  
disproportionately effect leaping launch evolution.

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu