[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Fwd: Science feather strength debate
>>> 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
>> 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
> 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.