Re: Science feather strength debate

[Erik Boehm <erikboehm07@yahoo.com>]

> Because even rudimentary forelimb movements can generate
> useful thrust... some thrust generation by
> these fossil birds cannot be discounted,
> but the vigorous flapping flight of modern
> birds is highly unlikely.
> 

I can see "some thrust generation" falling short of self-powered flight being 
useful in a ridge soaring scenario- providing a path to powered flight, one 
that seems to be lacking for arboreal gliders.

> Senter seems to be more conservative, arguing that flapping
> was
> precluded by the inability to execute the recovery phase of
> the
> stroke, due to the orientation of the shoulder joint
If you can power the downstroke, the upstroke (back to horizontal) should take 
care of itself, what am I missing?


> > Any keel at all would suggest some form of flapping to
> me.
> > If it is an attachment area for muscles for the
> wing... my imagination is insufficient to imagine what those
> muscles were used for if not flapping.
> 
> 
> _Mononykus_ has a keel.
> 
> 
> Now, I'm not in any way suggesting that basal birds used
> their
> forelimbs in the same way as alvarezsaurs (!)  I'm
> merely pointing out
> that the presence of a keel does not necessarily correlate
> with a flight stroke.  It's possible that the development of
> a keel in birds
> preceded the advent of powered flight, as did the evolution
> of the furcula, feathers, and elongated forelimbs.

The presence of a keel, indicates the forelimbs were doing something that 
required more power than could be delivered without the keel.
When your forelimbs are elongated with small claws, but covered in long 
aerodynamic feathers, and your descendants use the keel and forelimbs for 
flapping, it seems simplest and logical to assume the most likely reason for 
the keel, was flapping.

What I am suggesting, is these things went from some form of rudimentary 
gliding, to soaring, and during that soaring started powering their flight.
Maybe not enough to maintain level flight in stagnant air, but enough to 
broaden their options - extend glides to cross gap
 ridge, improve penetration into a headwind if it finds itself a little bit too 
far behind the ridge, etc.

RC and foot launched soaring enthusiasts will confirm, coastal ridge soaring is 
pretty much the easiest form of soaring there is.

So confuciusornis didn't live by the ocean...
#1) any sufficiently large body of water will have a relatively constant 
temperature, that when combined with the day/night cycle, will produce a 
reliable temperature gradient - which may result in reliable winds for soaring 
- I know that some of the "Great Lakes" of the US produce winds, and have 
dunes, that result in reliable soaring conditions.
Also, I know of a ridge about 100 km long in the desert of Utah bordering 
Arizona, that is regularly soarable. 
And there is also "point of the Mountain", Utah, with a "north" and "south" 
side, and one or the other is reliably soarable. (and soarable by a wide margin 
at least for setups between wingloadings of 1.5 lbs/ sq foot on a 5.4 aspect 
ratio wing, and wingloading of 2.0 lb/sq foot on a 7.3 aspect ratio wing 
-youtube video links demonstrating this margin upon request)

Coastal soaring is not the only type of ridge soaring, it is just the prime 
example - the coast has a good correlation with conditions for that kind of 
soaring - so it intrigues me that the earlier Archy lived close to a coast.

Seeing as how a "ridge" that is suitable for soaring may only be about a meter 
high (provided the rest of the terrain is rather flat, and the ground is free 
of obstructions that would slow the wind and cause a gradient, such as a desert 
with little vegetation, or the surface of water and a shoreline), a lack of a 
discernible ridge or series of them where Confu. was found, does not rule out 
the possibility that it primarily soared, rather than flapped or climbed trees.

#2) It obviously had many flight adaptations (*cough* keel *cough*) relative to 
earlier "birds", so it seems one needs to look earlier for whatever was 
selecting for those adaptations.
If it had all these flight adaptation, but ye
 powered flight.... what were those adaptations for? that seems like an awful 
lot of adaptation for gliding between trees - what difference does it make to a 
tree-glider if it gets a 7:1 or a 14:1 glide ratio?
Gliding to a tree 70 feet away, you'd only save 5 feet worth of climbing to go 
from 7:1 to 14:1, but it seems the forelimb modification required for that 
would have severe limitations, particularly if you expect this thing to climb, 
which as many note, it shows no adaptation for.
Likewise what advantage would there be to reducing sink rate from 2m/s to 1 
m/s, to a tree-glider? there would be a huge advantage to a soaring animal.
I have to conclude it was engaging in some form of flight behavior, 
Tree-gliding just doesn't make sense to me - it doesn't explain a keeled bird 
with high aspect ratio wings, when a low aspect ratio flap of skin (as in a 
flying squirrel) would be nearly as good for that purpose.
If it wasn't capable of powered flight, the next most logical explanation as I 
see it, is that it soared.

The way I see it, something with the gliding capability of a loon (but not a 
loon's powered flight capability), should be able to soar just fine, and in 
some areas, cross large distances via thermalling flight.
People can do it with machines that do not exceed a loon in L/D, but exceed one 
in wing loading - while having a much larger turning radii.
You don't need to be shaped like a Vulture to thermal- but it is a big help.
You also don't need to be shaped like a gull to ridge soar, but that also helps.
In the absence of specialized forms like gulls and vultures, I can imagine a 
archy/confuciusornis bird being viable by soaring, without powered flight.


btw, was it ever established if archy was actually missing feathers inward of 
the elbow when it was alive, or if it was a preservational artifact?