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Re: Science feather strength debate



I was referring to Greg Erickson, who you referenced in your post. Sorry about 
the confusion.

--Mike

Sent from my iPhone

On Nov 4, 2010, at 2:25 PM, Jason Brougham <jaseb@amnh.org> wrote:

> I think that was me, Jason, not Greg you were responding to.
> 
> -Jason
> 
> 
> On Nov 4, 2010, at 11:44 AM, Mike Habib wrote:
> 
>> Indeed, feather asymmetry is complicated, to an extent. Greg is mostly 
>> correct in his description, but not quite precise. The asymmetry dies affect 
>> twist, and feather twisting in the outboard wing is indeed important (though 
>> they twist on both strokes, and 'air resistance' isn't quite the right term, 
>> but I know what he's getting at).  The catch is that symmetrical feather can 
>> provide the same kinematics, but it requires more material.
>> 
>> Cheers,
>> 
>> --Mike H.
>> 
>> Sent from my iPhone
>> 
>> On Nov 4, 2010, at 11:32 AM, Jason Brougham <jaseb@amnh.org> wrote:
>> 
>>> Feather asymmetry is a complicated topic.
>>> 
>>> I've talked with people who have suggested that asymmetrical feathers may 
>>> have originated for some non - aerodynamic purpose, like tighter wing 
>>> folding, but I would tend to think they evolved in a gliding animal with 
>>> symmetrical feathers.
>>> 
>>> Greg Erickson pointed out that asymmetrical veins are not necessary for 
>>> lift - a frisbee gets lift. He said that the asymmetry actually functions 
>>> to allow the feather shafts to twist during a  flapping stroke - they open 
>>> and allow air between them on the upstroke (reducing air resistance), then 
>>> slam shut like louvre blinds on the downstroke, increasing resistance. Then 
>>> I  wondered aloud if Microraptor couldn't have flapped its legs too! It 
>>> seems ridiculous, but maybe the little bastards pumped their legs like 
>>> bicyclists in mid-air! I don't seriously think so, but Microraptor is such 
>>> a  puzzling animal. I don't know if I'll ever feel certain about anything 
>>> it did.
>>> 
>>> I should mention, though, that a priori and comparative conclusions are 
>>> useful and fascinating, but we always have to be ready to be persuaded by 
>>> new evidence.
>>> 
>>> As examples, some have argued that a bird can't engage in powered flight 
>>> without a supracoracoideus, but then Sokoloff et al. (2001) found that 
>>> starlings that had had their supracoracoids surgically removed could take 
>>> off from the ground just fine. 
>>> 
>>> When I was working on the NOVA episode The Four Winged Dinosaur I was sure 
>>> that the asymmetrical feathers on Microraptor's feet had to face toe - 
>>> first into the airstream. Logic dictated that asymmetrical feathers 
>>> wouldn't provide lift if you flew them backwards. But Dr. Xu wanted to try 
>>> them backwards, and we did it, and we got great lift from backwards 
>>> asymmetrical feathers in the wind tunnel! 
>>> 
>>> That's why, when we have discussions about extinct species based largely on 
>>> logic and comparative data, I always start to yearn for some experimental 
>>> data to test things. A bad experiment can mislead you, of course, but a 
>>> good one can be  a crucial reality check.
>>> 
>>> On Nov 4, 2010, at 10:44 AM, Don Ohmes wrote:
>>> 
>>>> 
>>>>> On 11/4/2010 9:14 AM, Mike Habib wrote:
>>>>>> Not to mention that asymmetrical feathers are not actually required
>>>>>> for flight, from a first principles standpoint, despite the now
>>>>>> popular notion that there must be a 1:1 correspondence.
>>>> 
>>>>>>> On Nov 4, 2010, at 7:19 AM, David Marjanovic<david.marjanovic@gmx.at>
>>>>>>> wrote:
>>>> 
>>>>>>>> However, some flightless birds retain asymmetrical vanes (e.g.,
>>>>>>>> flightless grebes)
>>>>>>> 
>>>>>>> Oho. Reference, please?
>>>> 
>>>> On 11/4/2010 10:09 AM, Don Ohmes wrote:
>>>> 
>>>>> The fact that some flightless birds *retain* asymmetrical vanes should
>>>>> not negatively affect the status of asymmetrical vanes as indicators of
>>>>> volancy.
>>>> 
>>>> Also -- if some flightless birds retain asymmetrical vanes, while others 
>>>> don't, and those birds that do not have them are "further" from their 
>>>> earlier volant state -- then that would tend to support the notion that 
>>>> asymmetrical vanes evolve under flight conditions, would it not?
>>> 
>>> Jason Brougham
>>> Senior Principal Preparator
>>> American Museum of Natural History
>>> jaseb@amnh.org
>>> (212) 496 3544
>>> 
>>> 
> 
> Jason Brougham
> Senior Principal Preparator
> American Museum of Natural History
> jaseb@amnh.org
> (212) 496 3544
> 
>