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Re: large fossil birds
The largest individual bird that I know of that flies by means of
continuous flapping flight is a male Whooper Swan that has been
designated 'JAP' by the folks who study him (I don't know if he is
still alive). I'm probably too close to pterosaurs, because I think
of him as being 'relatively' low aspect ratio...
I have an average measure of 8.7 for the aspect ratio of whooper swans.
As birds go, this is reasonably high (about the same as most falcons,
though well below seabirds and swifts). Being used to pterosaurs would
give a very different view of things, I'm sure. Your original point
may still hold if phylogenetic patterns are taken into account,
however. While whoopers don't have low AR's for birds overall, it is a
bit on the low side compared to other (smaller) anatids. So it may
turn out that there is a negative relationship between aspect ratio and
size to a degree if one uses contrast analysis instead of raw species
values (at least for some groups).
My impression for pterosaurs is that takeoff didn't involve a bunch of
mad flapping or running. My perception is that they sidestepped the
power required versus power available issue that limits birds, and did
so by using a launch technique that reduced the power requirements on
the pectoral muscles... ... With regard to landing, being quadrupedal
on the ground was a huge asset in avoiding the pitfalls of the fanny
over teakettle technique used by albatrosses.
Sounds very reasonable to me, for whatever that's worth. It also sets
up a rather interesting possible tradeoff situation between
launch/landing system and locomotor bimodality (ie. birds are more
limited in launch and landing in some cases, but have the advantage of
multiple locomotor modules).
Given a wind, they aren't too low along the margins of lakes. And
again, high aspect ratio animals can effectively use convective lift
too. In fact, they find it easier to travel inland than do lower
aspect animals, with their lower lift/drag ratios. As an
oversimplification, about 20% of the sky is covered by updrafts, 80%
with downdrafts. You want to be able to move through the downdrafts
between updraft areas as efficiently as possible, and high aspect
ratio and high wing loading both facilitate that (particularly with
the facility for occasional burst flapping).
I didn't realize lake effects were so strong; that's really quite cool.
I agree with your point about moving between updrafts and the
advantages of high aspect ratios over land. I would add the caveat
(that I know you're well aware of, but others may not be) that riding
inland thermals will often require lower wing loading in order to
maintain slow speeds required for tight turning to stay in the thermal
updraft. Thus, there is some give and take in wing loading, especially
for species that are very reliant on smaller thermals for gaining
altitude. Thus, I wouldn't expect overland flyers to always be
selected for high wing loading (which matches the wide range of
loadings actually demonstrated by large inland birds).
Paul MacCready has used spanloading to enormous benefit in several of
his aircraft. you can get a quick insight into spanloading by looking
at some of them.
Excellent, thanks for the tip.