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Re: Senter 2006, Confuciusornis, and humeral mobility



On Mar 27, 2011, at 5:57 PM, Don Ohmes wrote:

> I have a LOT more confidence in the quality of a concrete binary 
> observation, e.g., "...the bird could not fly (UNTIL he emptied his 
> crop, or the wind started blowing, or he reached a steep slope, 
> etc)...", than in a guess about whether the wind was blowing (and how 
> hard) on the occasions when he did fly.

Except that it isn't actually concrete binary data - how do we know the animal 
could not fly?  The observation is that it did not fly until it emptied its 
crop or a gust came along.  That does not tell us that the animal *could* not 
launch, only that it did not do so.  I agree that it's suggestive, but without 
a real controlled experiment it's difficult to interpret.  Regardless, the 
situation appears to be a fluke of condors, specifically, and not of anything 
specifically to do with size - CA condors are big birds, but they're not really 
all that huge.  The span is exceptional (something like 2.8-2.9 meters for an 
adult), but the average adult mass is only 8-9 kg.  The average male Kori 
Bustard, by comparison comes in at 12-13 kg; about 40-50% heavier.  Bustards 
are adept ground-launchers.

> i don't get what you mean about failed launch data being unreliable 
> (assuming enough observations).

Because what is usually observed is not a failed launch, but lack of launch - 
so the observers tend to presume that the birds are incapable of takeoff.  That 
*might* be true, but it might not be.  I'm not suggesting that the general 
behavioral observations are useless, but they are tricky.

> By evolutionary logic I find the behavior compelling evidence, anyways 
> -- the CA Condor and that general body style have been regressing in 
> size a long time.

I'm not sure I follow you here - what do you find the CA Condor launch 
observations to be compelling evidence of?  How does "evolutionary logic" play 
into it?  

Oh, and be careful - it may look like there is a general trend in body size 
reduction among broad-winged inland soaring birds, but it's an illusion - we're 
missing any giant flyers right now, but they came and went throughout the 
Cenozoic.  So the appearance of a trend rests entirely upon the lack of any 
right now, which is the result of the Pleistocene extinctions (loss of 
teratorns, giant eagles, etc).  Besides, even if CA Condors really are limited 
in their ground-launch ability, they are the outlier - plenty of birds their 
size or larger with rougher similar planforms are successful ground-launchers.

Cheers,

--MH


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