Symmetric feather loss

gc genecutl at
Fri Jun 17 07:48:03 EST 1994

In article <1994Jun17.111816.1 at>, skrishna at
> 	I have recently observed a strange and wonderful phenomenon on my pet
> cockatiel.  He is an unusual color mutation called a "pearl;" the mutation is
> sex-linked so when a male pearl molts (loses feathers) for the first time, he
> also changes color from pearl to plain grey (more or less).  So I'm watching
> him change color.  This process is heralded by appearance of grey blobs on his
> body where old feathers have fallen out and the new grey ones have come in.  
> 	So, here's the cool thing:  the grey patches -- even tiny ones on the
> head and the front of the wings -- appear _perfectly symmetrically_ down the
> body line.  That is, when the bird loses a particular feather on its left wing,
> the same one will be lost and replaced at more or less the same time on its
> right wing.  This must be accomplished by quite a feat of developmental
> regulation!  I've watched a lot of pet birds molt before but only noticed the
> pattern of molting on this bird because of the color change.  
> 	Of course, it makes evolutionary sense.  The bird doesn't want to have
> all new feathers on one side and old, ratty ones on the other (or worse, be
> losing all the feathers on one side only), as that would impair its flight. 
> But the genetic process culminating in the periodic, symmetric loss of feathers
> must be quite elaborate.  Does anyone know of any research on this process?
> 	Thanks in advance for any ideas,
> 						Sanjay Krishnaswamy
> 						skrishna at

I would say that this molting pattern was probably not selected 
for but is only a consequence of selection for other things, that
being bilateral symmetry which goes back a lot further than parrots,
evolution-wise.  Bilateral symmetry is established early on in
emryonic development.  That's where the answer to your question
probably lies.

--g(actively being selected against)c

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