Harvey, having ready your message on birding-aus just a few points.
Feathers once fully grown are dead in that there is no blood/nutrient supply
to them. They can therefore only change colour in two ways 1) by fading and
2) by the tips of the feathers wearing away and exposing feathers
underneath. A very good example of this is the starling; all speckled at
this time of year because of the white tip to the body feather and later in
the year all the speckle goes, not due to a body moult but due to feather
wear. The body can sense if a feather is missing and a new one will grow to
replace it but if the feather is cut a new feather will not grow until the
next moult.
I see no reason why different wing shapes cannot be produced with different
moults, but I know of no bird that does this. (now I think about this of
course this can happen i.e. the 'banners" on the Nightjar but this is more
to do with courtship that changing wing shape). I presume a different wing
shape is more than different length feathers, it is also to do with
metabolism, muscle mass etc.
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