Harvey:
I am glad you enjoyed the article, but I have to admit that your
question is particularly creative and hasn't occurred to me (my wife love
it). I think Chris Davy's remarks are spot on, however there could be
unnoticed - to me, not full time banders, etc - variation in wing feathers
across different age groups or across males and females that directly
effect a bird's ability to fly long distances. If so, the precise timing
and duration of moulting could be important, i.e. before or after
migration, etc. Unfortunately, I can't think of any examples to
illustrate how this might work. Another possibility is the growth and
elimination of feathers whose use seem to be strictly ornamental (see
Chris' e-mail). Ornamental feathers could potentially hinder flight - one
reason they have evolved; I'll cover this topic in an upcomming IBB
article - if so, one would expect them to be disgarded before migrating.
Sorry, I can't give you any concrete examples off the top of my head -
tail streams,etc. is a possible example - at this point in time, but
others on the list may care to comment.
Cheers, Jim
Dr. Wm. James Davis
Editor, Interpretive Birding Bulletin
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