[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: New(ish) paper II




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."

_________________________________________________________________
FREE pop-up blocking with the new MSN Toolbar ? get it now! http://clk.atdmt.com/AVE/go/onm00200415ave/direct/01/