Re: large fossil birds

[don ohmes <d_ohmes@yahoo.com>]

--- jrc <jrccea@bellsouth.net> wrote:

> 
> ----- Original Message ----- 
> From: "don ohmes" <d_ohmes@yahoo.com>
> To: <mhabib5@jhmi.edu>
> Cc: <dinosaur@usc.edu>
> Sent: Thursday, December 01, 2005 8:12 AM
> Subject: Re: large fossil birds
> 
> 
> > +++++++++++++++++++++++++++++++++++++++++++++++++
> >
> > 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 unpublished data).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 is a Reynold's number effect.
> 
> >
> > This implies that the optimal AR within
> flightstyles
> > generally scales w/ size,
> 
> Agreed.
> 
> > and also that the AR at
> > which tip slots become unfavorable in falcon-sized
> > birds is lower than in pelican-sized birds.
> 
> I'd have to spend a few minutes thinking about this
> one.  It's a function of 
> the relationship between weight, speed, aspect ratio
> and profile drag.  At 
> first blush, I'd say its very likely true.  It is
> also a function of the 
> birds' line of ancestry, and random genetic
> variation and not entirely 
> related to aerodynamics.

I'm of the "optimizer" persuasion; but maybe birds
have more morphical slop than flies... actually they
do, but I think it is still limited. 

IMO-- Small diptera usually have near zero slop. In
insects, flightstyle determines optimal morphology;
within "high performance" flightstyles, ancestry can
be largely irrelevant.
 
> > It also (probably) explains why tip-slots
> disappear entirely
> > (IIRC) in smaller birds.
> 
> May well do.
> 
> > As previously mentioned
> > (again w/ the IIRC), comparisons between volants
> of
> > different sizes is basically iffy.
> 
> If Reynolds number effects are taken into account,
> I'm not sure I'd agree 
> with this.  I do recognise that there are
> substantial limits on comparisons 
> between extreme differences in size.

I assume you mean mathematically. M. Dickinson is the
only one I know of that accounts for Re
experimentally, although I am not current; is there
even a working variable-pressure wind tunnel around
anymore? 

> > Does anyone happen to know what the smallest bird
> w/
> > tip-slots is?
> 
> Good question.  I don't know.

Drat. Hoped you might know.

Don 


> 
>