Symmetric feather loss

skrishna at skrishna at
Fri Jun 17 11:18:16 EST 1994

Hi, there, netfolk!
	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

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