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Re: Senter 2006, Confuciusornis, and humeral mobility



On Mar 25, 2011, at 10:52 PM, Jason Brougham wrote:

> What besides span and loading determines the stroke angle?


It's also related to the speed, though speed does correlate with wing loading 
(in soaring flight, wing loading is the primary determinant of speed).

On Mar 25, 2011, at 11:40 PM, Jason Brougham wrote:

> So let's just stick to your original suggestion that we just consider
> steady flight for now.

Sounds good to me.  Just keep in mind that we have to get it into steady 
flight, first.

> We know that there are many modern birds, such as
> Shearwaters (http://www.youtube.com/watch?v=Cjmtt_B_i4A) and condors, that
> have great difficulty getting airborne yet they may still live much of
> their lives on the wing.

Be careful with this.  The "it can't take off on its own card" gets played A 
LOT for various kind of birds, and for most of them, it's bunk.  Shearwaters, 
for example, can take off from a level surface without any problem at all if 
they have sufficient room.  The forest nesting taxa do not, so they climb trees 
to launch, but their equally-loaded brethren just punch it from a short run on 
the ground or water.  Condors are constantly referred to as being incapable of 
launching without gusts, but no one has ever shown this to be the case, and 
videographers have caught them ground-launching in still air under duress.  The 
key is that they only do it when pressured because otherwise it's too energetic 
to be worthwhile.  Some of the large vultures, near the loading and size of 
condors, actually launch from a standstill, so I find the condor arguments 
extremely dubious.

Note that in order to perform WAIR up a tree, a bird actually needs quite an 
advanced upstroke and the ability to build a negative lift coefficient.  So 
WAIR is not clearly any "easier" for an adult bird than just taking off from 
the ground except to the extent that birds can apparently WAIR with very high 
wing loadings (hence why it works for juveniles without full wings).  Since 
shearwaters do not have prohibitively high loadings for launch (we know this 
comparative data; most shearwaters are not forest taxa), the WAIR usage must be 
related to clearance, and not power.


On Mar 25, 2011, at 11:50 PM, Jason Brougham wrote:

>>> What mass are you using, Michael?
> 
> 
>> I ran a range from 150-180 grams.
> 
> Wow! The Black kite is apparently 650-950 grams with the same wingspan! So
> Confuciusornis must have way, way, less wing loading (1/3.6th at most)
> and, thus, must have needed even less of a stroke angle! So I think we are
> on the verge of proving it was  a powered flier.

Be careful here - lower wing loading species tend to flap with a *greater* 
stroke angle in cruising flight because they fly more slowly.  Also, I was 
using a suggested literature value for the mass of Confuciusornis, but the 
specimen I measured was quite large, so it is probably heavier than I 
estimated.  Don't fall into the trap of "high loading makes everything harder" 
scenario - wing loading is a tradeoff system.

> 
> Please watch these Sooty Shearwaters using WAIR to climb trees so that
> they can takeoff. These things have webbed feet, no arboreal adaptations,
> and apparently don't have the power to takeoff from the ground:
> 
> http://www.youtube.com/watch?v=Cjmtt_B_i4A
> 
> Can't you picture Confuciusornis doing the same thing?

I cannot, unfortunately, because of the very problem we started with - the lack 
of extensive abduction at the shoulder would pretty much kill WAIR.  Also, see 
above: it's not a power problem (the show implies that it is, but they are 
incorrect; many documentaries make mistakes about flight, especially when 
discussing soaring taxa).

> Yet Confuciusornis DID retain a jointed wing finger which opens the 
> possibility that it could modify the configurations of its primaries, thus 
> radcally changing the shape of the wingtip (possibly even rolling it up 
> and/or cupping it). The motions of the fingers are crucial in the flight of 
> bats.

That allows for the generation of a high lift and high drag configuration in 
bats; great for flying slowly, but it does not reduce the flapping amplitude 
(at a large lift coefficient the flapping amplitude is usually greater).


On Mar 26, 2011, at 3:50 PM, evelyn sobielski wrote:

> Different reasons although it is fundamentally the high wing loading. Both 
> use different kinds of soaring and have optimized winds for each purpose. 
> Procellariiform (and generally pelagic birds') wings are optimized for 
> prolonged flight above (and bouncing on, sort of) ground effect; they are too 
> narrow in take-off but overall such birds are not particularly heavily built 
> (even albatrosses). Their wingspan evolved beyond a point where takeoff is 
> easily possible/their body mass couldn't follow suit.

For a rapid glider, such as an albatross, there is a distinct advantage to 
having the highest wing loading at which launch is still feasible.  Even very 
large, heavily loaded albatrosses can take off from the water surface, so they 
are still take-off capable, but the high loading and aquatic adaptations place 
heavy constraints on this system.  Interestingly, pseudodontorns are known to 
have had high aspect ratio wings and a body plan similar to procellariiform 
birds, but reached much greater sizes.

Cheers,

--Mike H.