Re: FUCHSIA and the Ostrom Symposium Volume (long...)

[Graydon <graydon@dsl.ca>]

On Sat, Aug 10, 2002 at 04:24:40PM +0200, David Marjanovic scripsit:
> From: "Williams, Tim" <TiJaWi@agron.iastate.edu>
> > Ostrom provided a step-by-step, gradualistic scenario on
> > how a prey-catching forelimb might have changed over to a lift- and
> > thrust-generating wing that carried the insect-eating biped into the air -
> 
> The step from the forward stroke to the downward stroke is missing, though.
> (OTOH, the forward stroke looks just like what I can see in the video of the
> vertically running bird... or this may be false memory. Gotta look again.)

Forward stroke to downward stroke is an angle change; there's an obvious
advantage to a cursorial predator in being able to apply the predatory
stroke over a wider range of angles.  (Since you can adjust for dinner's
desperate deeking better that way.)

If the useful predatory angles and the useful aerodynamic propulsion
angles -- which includes anything that enhances running for any purpose
-- overlap, no specific step is required to posit such a transition.

If you're looking at _why_ a running animal would flap, well, presumably
a cursorial predator needs to apply the predatory stroke _while it's
running_.

That being the case, it really isn't a stretch to have the range of
flapping behaviours expand; all it takes is some advantage -- in
turning, or in traction, or in clearing an obstacle -- accrue to
'premature' use of the predatory stroke while outside of striking range
in pursuit.

Early use in turn can be explained by normal behaviour variation; some
predators are more optimistic than other predators, and figure it's
worth a try even when the odds are bad, and sometimes it helps balance
to stick out a limb; either or both of those suffice to get onto that
particular gradual ramp of moving toward the flight stroke from the
predatory stroke.

-- 
graydon@dsl.ca   |  Hige sceal þe heardra, heorte þe cenre,
                 |  mod sceal þe mare þe ure maegen lytlað.
                 |   -- Beorhtwold, "The Battle of Maldon"