Fwd: Science feather strength debate

[Jason Brougham <jaseb@amnh.org>]

>> 
>> 
>>> a 20% difference in mass makes a big difference in aerodynamics and 
>> 
>> This is ridiculous. The mass of an individual bird can vary by 20% or more 
>> over a matter of hours (if it gorges) or days (as body fat deposits vary). 
>> It is common for very long distance migrating birds to start out heavy with 
>> fat and lose it by the end of the journey. The bird can effectively fly at 
>> the beginning and end of the mission. In any case, as I have stressed 
>> repeatedly in the literature, it is not possible to restore the mass of an 
>> individual specimen better than +/- 20% or more because of problems with 
>> restored 
>> volume, SG, and normal changes in an individuals mass. The problem with the 
>> Nudds and Dyke was that they overestimated the mass of the Archaeopteryx 
>> specimen they examined by a factor of about two, Confusicusornis by about 
>> three. 
> 
> If 20% doesn't matter then I wonder why you bothered adjusting Yalden's 
> estimate for the body mass of HMN 1880 by 13% (from 271 to 234g). You also 
> spend some time discussing the relative merits of a pectoralis mass between 5 
> and 15% of body mass.
> 
> Moreover, we would both agree that 20% doesn't matter to extant migratory 
> birds with highly derived flight apparatus, but modern birds have a lot of 
> spare capacity. They can stoop at 200 mph, hover in mid air, and fly 
> thousands of miles! In an animal that is barely capable of aerodynamic 
> locomotion, like any hypothetical ancestor of birds, 20% could be a crucial 
> difference between ascending flight and gliding.
> 
> I agree that Nudds and Dyke used mass estimates that are too high and rachis 
> measurements that were too small, and that their conclusions must thus be 
> reconsidered. But Zheng et al. found that Nudds and Dyke still demonstrated 
> that both birds had weak rachises compared to extant birds of the same mass. 
> I still think they flew, but this contribution by Nudds and Dyke suggests 
> that Confuciusornis probably couldn't pull the miraculous maneuvers (pouncing 
> on fish and then taking off from the water surface) that kingfishers do today.