Re: large fossil birds

[Michael Habib <mhabib5@jhmi.edu>]

> 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.

--Mike