[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Senter 2006, Confuciusornis, and humeral mobility



On Mar 27, 2011, at 10:44 AM, Don Ohmes wrote:

> On 3/26/2011 5:59 PM, Habib, Michael wrote:
>> Shearwaters, for example, can take off from a level surface without any 
>> problem at all if they have sufficient room.
> 
> Could you clarify, perhaps by citing a species that has one, what you 
> would consider qualifies as a 'takeoff problem'?

Frigatebirds have greatly constrained launch scenarios.


>> Condors are constantly referred to as being incapable of launching without 
>> gusts, but no one has ever shown this to be the case, and videographers have 
>> caught them ground-launching in still air under duress.
> 
> How do you know the air was still? Was the slope level? What was the 
> crop condition of the subjects? Full, empty, something in between?

Lack of motion in the flora suggested still air, the slope was level.  No way 
to tell what the crop condition was.  I suspect that the stories of condor 
launch restrictions come mostly from animals that had just fed very heavily.  

It may be that some condors do require, or at least greatly prefer, gust 
launching after heavy meals.  There are really not enough data to say for 
certain.  The main problem is that there are so many anecdotal accounts of 
limitations on condor launching, without rigorous data, that are taken at face 
value because the animals are "big", and many readers are willing accept that 
"big" flyers must have difficulties in launching.  The resting wing loading of 
a CA Condor is about 7.7 kg/m^2, which is relatively high for a large bird, but 
not extreme - other large birds with similar loading launch are known with 
confidence to launch without special conditions.  If condors had reduced hind 
limbs, then that would limit their launch power, but andean condors, at least, 
have strong hind limbs (though they are a bit weaker, relative to body size 
expectations, than some of the other New World vultures).  Perhaps CA Condors 
have weak hind limbs, I can't say at this time.  My general point is just to be 
careful taking anecdotes about takeoff at face value.  There are texts that 
claim running launch is related in a simple manner to body size, as well, just 
for example, and we know that isn't true.

Cheers,

--Mike H.


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181