[CT Birds] Hairy Woodpecker with yellow patches on head
raask at conncoll.edu
Fri Jan 11 20:26:28 EST 2013
I asked Alan Brush, who has done extensive research on the structure and
pigmentation of feathers, about the Hairy Woodpecker with yellow rather
than red patches on its head. His response is below.
My thought is that on adult bird, the plumage would have been replaced
pretty much completely by the end of summer, eg., this is the basic
plumage. There is nothing in the literature I can find, that reports this
change in this species. So here are the alternatives.
1) dietary, as in HOFI or CEDW. That is, some new or different food source
during moult. If that were the case, I would expect it to be a little more
wide spread or common. While HAWOs are not as common and feed over wider
areas, the frequency in the NE would be expected to be lower. Simply a
sampling problem. My guess would be that a dietary change is not the case.
2) a mutation or other type change in the metabolic pathways that changes
the precursor carotenoid into the form deposited in the feather. Although
this species mainly eats animal food (although I can't think of it as a
'predator'), mostly beetles, grubs, spiders, etc, they also take fruit and
seeds. That means they get not only a variety of carotenoids in their
diet, it's available year round. Where the 'error' resides in this
individual may be the malfunction of an enzyme in the pathway from
precursor to product or in the mechanism that transports molecules or
incorporates them into the follicle. A change in any of these could produce
the change in the nape feathers. Since carotenoids are not deposited in any
other tract, it's not a more general problem. On could, of course,
discriminate among these possibilities with a chemical analysis of the
feathers from this individual and a 'normal' feather.
That's the best I can do from here (keyboard rather than a lab)
Alan H Brush
brushes2 at juno.com
More information about the CTBirds