orange-tipped waxwings/diet?

["Rob G" <thrush@hotmail.com>]

  I've been seeing the orange-tipped waxwings for probably at least 10 yrs. 
now (in fact hardly ever see a large flock, 40 or more, without
one of these fellas) but had always heard it to be a genetic mutation.

  Since waxwings flock and eat from the same sources one would expect much 
higher numbers of birds to show the trait if it were a simple  matter of 
diet, so I suspect at root it's technically a genetic matter (although diet 
may trigger the genetic trait to 'express' itself while having no effect on 
birds lacking the mutation).

**Rob Gluck     thrush@hotmail.com     Chapel Hill
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