Re: large fossil birds

[don ohmes <d_ohmes@yahoo.com>]

--- Michael Habib <mhabib5@jhmi.edu> wrote:

> 
> >>  Thus, I wouldn't expect overland flyers to
> always be selected for 
> >> high wing loading
> >
> > Nor would I.  It depends upon the specific niche
> they are filling and 
> > their usual source for atmospheric energy
> extraction.  Birds are more 
> > versatile in that regard than pterosaurs were. 
> Birds exhibit 
> > variations on more than one theme.  Pterosaurs
> exhibit variations upon 
> > a single theme.  You've probably noticed that
> birds with low to 
> > intermediate aspect ratios find tipslots
> advantageous while higher 
> > aspect ratios shift to triangular wingtips.
> Pelicans are right on the 
> > morphological dividing line between the two forms,
> and as far as I 
> > recall, are the highest aspect ratio birds to make
> use of tipslots.  
> > For birds with aspect ratios less than pelicans,
> there can be an 
> > advantage to reducing wingloading.  For birds with
> larger aspect 
> > ratios than pelicans, the advantage would usually
> seem to be toward 
> > increasing it...
> 
> I am not aware of any birds with AR's higher than
> pelicans that utilize 
> tipslots either.  In fact, a fair number of birds
> with AR's 
> significantly lower than pelicans have tapered
> wingtips without slots 
> (falcons, for example, though they are not exactly
> typical birds).  
> There are also differences in how the wings are held
> across birds with 
> different AR's.  For example, those with high aspect
> ratios tend to 
> hold the tips of the wings angled slightly downward
> and back 
> (especially by marine birds during rapid soaring). 
> If I remember 
> correctly, this serves to form more favorable vortex
> patterns at the 
> distal portions of the wing and thus reduce drag
> near the tips, but my 
> memory may not be serving me correctly on that one.

+++++++++++++++++++++++++++++++++++++++++++++++++

In wild type D. melanogaster (and drosophila
generally), AR increases with size. Even a small
sample of males ranging .5-.95mg will conform to this
trend (p <.05), and given controlled conditions, AR
increase can be consistently (75-80%) measured between
flies with a weight differential of .1 mg! (Don Ohmes,
unpublished data). In insects, the correlation seems
to hold across taxa, _within wing (and presumably
flight) styles_. 

This implies that the optimal AR within flightstyles
generally scales w/ size, and also that the AR at
which tip slots become unfavorable in falcon-sized
birds is lower than in pelican-sized birds. It also
(probably) explains why tip-slots disappear entirely
(IIRC) in smaller birds. As previously mentioned
(again w/ the IIRC), comparisons between volants of
different sizes is basically iffy.

Does anyone happen to know what the smallest bird w/
tip-slots is?

Don

++++++++++++++++++++++++++++++++++++++++++++++++++

> In fact, wing shape changes during different flight
> modes are often 
> ignored (as far as I can tell) in discussions of
> flight.  For example, 
> the 'classic' picture of vultures (which is the
> image generally 
> illustrated) is one with the wings held out at
> maximum span and the 
> tipslots fully open.  However, this is mostly the
> case during loitering 
> and landing.  If you can catch vultures moving
> between updrafts you'll 
> notice that they bend the wings and close their
> tipslots.  So, in that 
> case, wing loading is behaviorally increased during
> travel between 
> updrafts.  I'm not sure how the mechanics of wing
> shape changes during 
> flight would work for pterosaurs with their unique
> wing membrane.  
> Would they be limited in their ability to fly with
> shortened wingspans 
> due to disruption of the wing surface by membrane
> folding?
> 
> >> I didn't realize lake effects were so strong;
> that's really quite 
> >> cool.
> >
> > They are only strong given a wind plus a vertical
> discontinuity along 
> > the shoreline (either bank slope or treeline, or
> both)... Note that 
> > the only reason for maximising chord and
> minimising wingloading in 
> > convective lift is to assure that the average
> minimum sink rate is 
> > less than the average convective updraft.  Once
> that condition is met, 
> > the advantage shifts to the highest aspect ratio
> and highest 
> > wingloading that will meet that restriction,
> because the latter two 
> > characteristics help in traversing the downdrafts
> between updrafts....
> 
> Again, a need anecdote from good ol' vultures:
> during some walks along 
> a very large lake with a distinct treeline I noticed
> not only a very 
> strong wind (even at ground level), but had the
> enjoyable experience of 
> watching about 6 or 7 vultures riding the wind
> shears.  Not 
> surprisingly, they were using the flexed, more
> highly loaded wing 
> configuration I mentioned above (and were really
> moving hard...using a 
> couple of known landmarks I got a rough estimation
> of 40-60 mph for a 
> couple of them.  Considering how one usually catches
> turkey vultures 
> moving, that's really cookin').
> 
> Cheers,
> 
> --Mike
>