Re: New(ish) paper II

["Tim Williams" <twilliams_alpha@hotmail.com>]

T. Michael Keesey wrote:

> Or are they just saying that what goes up must come down?  Like, okay, you 
> got
> up the tree using WAIR ... now how are you gonna get down??

That's my impression.  But why just a tree?  There are other substrates that 
are inclined, such as hillocks or dunes or rocks.  (I'm not critizing your 
post; the paper refers specifically to trees.)

> (It's not phrased clearly, unless I'm missing something from the context.)

It isn't phrased clearly.  If I understand WAIR correctly, this behavior is 
proposed to have engendered the flight stroke; but there is no compulsion on 
the part of pro-avians to try and use their incipient wings to descend from 
the height immediately after they have ascended the tree (or hillock or rock 
..).  I could be misunderstanding the authors' intent.  To be fair to the 
authors, here is the complete paragraph...

"Another peculiar but interesting deviation of the tree-down model is based 
on the recent observation of a behavior of partridge chicks (Alectoris 
chukar) rapidly and strenuously ascending nearly vertical surfaces, to which 
the running feet were applied by thrust from the flapping wings, before 
falling into flight ([Dial (2003]). To the problems of air resistance, 
surface friction, and great energy expense (see [Long et al (2002]), another 
form of drag becomes paramount (Dclimb). Not only must the climber have in 
reserve sufficient energy for great vertical acceleration, but also a small 
body mass. The usual understanding of the tree-down model is that the 
climbing is a separate energy cost not expended so suddenly and so close to 
the time of gliding. We have proved in our paper that Vymax limits Vxmax, so 
that we would predict that a rapidly ascending partridge chick is limited 
from moving far or fast in a horizontal direction without continuous induced 
power. Were it not for what we have described as flutter-gliding, to soften 
impacts on landing, an accelerating vertical climb and subsequent fall would 
confer limited survival and evolutionary fitness. If these partridges are 
relevant to flight evolution, they do not exemplify either of the classical 
theories but do fit in our synthesis."

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