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Re: Pterosaurs and birds, was Re: birds and pterosaurs



Very interesting thought. However, as was already mentioned via Argentavis, there have been some truly large birds as well (far larger than extant forms). Some pseudodontorns, for example, had wingspans around 7 meters across.

I'm not sure what you mean by scaling in the "flesh" part of wing; the amount of muscle and connective tissue is indeed important to the mass of the wing, but growing a wing especially long generally requires longer bones, longer associated muscles, and longer feathers (ie. all structures increase in length). Also, feathers are very light, and larger feathers do not necessarily scale as quickly in mass as might be expected, because they are hollow structures (and can be made with thin keratin walls at large sizes). Does anyone know how feather mass scales with length?

Feather moults usually occur in a staggered fashion, so this helps to alleviate the problem of balancing replacement and the need for a suitable airfoil at all times. Still, the point is interesting, and I wonder what the variation in feather growth rate is across birds. After all, feather growth rates and wing weight would have to be limiting at some size, the question is whether this size would be above or below the limits by mass alone. If we can get some scaling equations worked out for feather weight, wing weight, and feather growth it might be a viable thing to work out. First thing to do is check if it's actually been done already; time to hit the literature...

--Mike


On Saturday, October 8, 2005, at 03:23 PM, Jorge Dichenberg wrote:


Just to hijack the thread.

I learned that flight feathers of large soaring birds
grow slowly, ca. 1mm/day. This means that largest
flight-feathers of vultures and pelicans take 3-4
months to grow.

I suspect that feather length and not body mass is
limiting size of flying birds.

Bird needs to replace flight feather by moult at least
every 2 years, cannot lose too many feathers without
becoming flightless, cannot feed while flightless (I
talk about specialised flying scavengers and
fisheaters) and thick base of feather means that
extending wing by growing the flesh part of wing
results in very heavy wing. Ergo - there is some limit
of bird wingspan.

Possibly for very large flying animals, wing membranes
are more efficent than feathers, models of animal
flight based on largest birds are biased and
pterosaurs achieved true limit of size of flying
animal.

Jerzy Dyczkowski

PS. I am aware that ornamental bird feathers are
longer and birds feeding on water plants can become
flightless during moult.




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