Re: Fw: Pterosaur size

[Michael Habib <mhabib5@jhmi.edu>]

> Not particularly.  Diomedea exulans has a glide ratio of about 
> 19-20:1.  I
> rounded off to 20 for convenience in multiplying.
> ---- that is high, as in upper end.

It's quite good, yes, but many of the fossil species we are discussing 
did even better.  Pelagornis managed 27:1.  Some pterosaurs did just as 
well or better.  Note that we have feather impressions for 
pseudodontorns, so planform is known with a fairly high degree of 
precision. --MH

> (<=== Relative to how the albatross gets there, see sink rate, minimum 
> stall and air circulation patterns through geological time. Last I 
> checked, the air circulation trend was more air circulation globally 
> (from past to present), which has implications for ancient soarers.)

True, ancient circulation patterns would probably have an effect on 
preferred foraging routes and such.  In any case, getting to 1000 feet 
is not a problem for any of the soaring species we're discussing, 
regardless.  You may assume cloud street usage, shear extraction, 
flapping gains, etc. depending on your preference.  --MH

> -------------- First answer got chopped out, I'll expand. Gets chopped 
> out again, I will resend. Dredging this up from memory, if I have been 
> wrong all these years, so be it. L/d= glide ratio. Sink rate increases 
> w/ weight, as does minimum stall. More to the point w/ biosystems, 
> increase in density = decrease in effective weight _WITHOUT LOSS OF 
> POWERMASS OR FAT RESERVES_. Equal power, less "weight", lower sink 
> rate/stall speed and more fuel/range.

So with the lower sink rate, the travel time between any given points 
increases; which isn't going to be beneficial to most pelagic birds.  
As Jim already said, the glide distance is not going to change, so the 
fuel/range ratio is left unaltered.  In the end, a pelagic bird (or 
pterosaur) probably just ends up increasing loading by reducing span a 
bit and the scenario ends up looking basically like the standard 
atmosphere scenario.  --MH

> People speak of kinematic adjustments. These are MORE beneficial at 
> higher density, as sink rate, etc. can ALWAYS be increased through 
> planform adjustment.

Actually, sink rate cannot always be increased through planform 
adjustment, but it can be for the ranges of changes we're discussing.  
Bats, in particular, have limited span reduction ability (flutter 
problems, etc.)  They do have great camber control, though. --MH

> Also braking power is improved. No way this is not massively 
> beneficial to a large bird, ESPECIALLY FROM THE ECOLOGICAL > PERSPECTIVE.

Actually, it is quite possible it would not be "massively beneficial".  
It might not be very beneficial at all, depending on how much the 
difference is felt.  After all, the benefits have to be weighed against 
the loss of sink speed (and thus travel speed for soaring birds).  Most 
large birds would probably barely notice.  Frigatebirds might notice 
the difference of small density shifts at launch altitude. --MH

> Increases in flight medium density (within reason) are beneficial to 
> volant biosystems at Re > 10, period. 15% is significant.

Er, not "period".  They have an effect, yes, but it is probably minor 
unless the increase is quite large.  Oh, and I do agree that at around 
Re=10 to 100 or so, the difference would be substantial.  At Re > 
100,000 (small birds), I'm more dubious because the fluid circulation 
won't shift as markedly.  As for 15% being significant, it depends on 
what you mean by "significance".  If you mean that small flying species 
might see altered flow regimes, or that large flying species might 
alter planform, then I agree.  If you mean that a swath of large-bodied 
taxa suddenly gain the ability to launch more effectively, then I am 
more dubious.  Again, it might be significant for species that are at 
the very limits of their launch ability for their morphotype.  This 
could apply to say, frigatebirds trying to launch from the ground 
(without gravity assistance), but it does not apply to most running 
launch seabirds, to pseudodontorns, or to pterosaurs.  Large 
pterosaurs, interestingly enough, were probably further from a 
launch-constrained size maximum than the large birds in question.  
Confirming that fact requires a biomechanical perspective; the 
selection gradients are too complex to use models of selection trends 
to determine the performance of large extinct flying species.  Of 
course, once the performance trends are quantified, we can use them to 
inform all sorts of interesting evolutionary questions.  --MH

Cheers,

--Mike H.