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Re: If Dinosaurs Could Fly






>On Mon, 19 Jan 1998, Matthew Troutman wrote:
>
>> >
>> >This is not to say, though, that contour feathers can have no 
>> insulating
>> >function.  More to the point, it says nothing about the insulating
>> >properties of "protofeathers", if that is what the structures on
>> >Sinosauropteryx really are.  And it avoids other possible uses of 
body
>> >feathers such as display.
>> 
>>       The only true insulatory feathers are the degenerate ( lacking 
>> derived barblets) of ratites and flightless birds. Down is not an 
>> effective insulator in wet conditions. One of the main causes of 
infant 
>> mortality in juvenile birds is when the down feathers get wet and 
they 
>> die of hypothermia. Pretty maladaptive.
>
>DOwn is not entirely maladaptive. It does have its points, one of which 
is
>to trap heat and baffle wind away from the skin. Juveniles that go 
through
>a down phase do so when they are confined(either by lack of motive 
ability
>and general helplessness or by parents) to the nesting area and 
therefore
>more likely to be protected from the elements. The transition from
>nest-bound chick to mobile juvenile is a dangerous time anyways and 
dying
>from hypothermia is probably about as likely as being snagged by a
>predator or breaking your neck learning to fly.  

     First of all, let me point out that I did not mean that down ( as a 
whole) is maladaptive. Only as a > single< insulatory pelage in wet 
conditions. Juvenile birds when they do not have sufficient shelter        
( parent, nest, coop, etc.) are incredibly susceptible to dying of 
hypothermia ( this applies to when they only have down). You ever see a 
downy wet bird? Its pretty messy because the feathers are all mucky. 
Down is very very good insulation when is covered by other feathers and 
the bird can stay very warm if it is aquatic, semi-aquatic, living in 
wet conditions ( ducks for example). And I do agree that predators and 
learning to fly are factors in juvenile mortality, but no more than wet 
down.


> > 

>> 
>>      Down feathers and filoplumes can be traced to contour feathers 
>> quite easily. And as stated above down as insulation is maladaptive
>
>
>Perhap as an overall lifespan strategie of insulation yes, buI wouldn't 
be
>so general. If it were a complete and utter failure then it wouldn't 
show
>up at all having  been selected against. 

 I agree.

>>      I agree here. There must be in essence a " pre-contour/flight 
>> feather".
>
>Me too....

Thanks.
>
>---Steve
>

 WMattTroutman

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