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



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