Definitely molting. Most of our waterfowl have a summer molt and a fall/winter/spring molt.
It makes sense to compare body (contour) feathers to shingles on a wall or roof. They overlap extensively, and a relatively small part of each is exposed. Compare a bird molting some of these to a wall or roof with some shingles missing (unfortunately the shingles won't grow back). This results in exposure of normally covered parts of the feathers/shingles under the missing ones. The pale-looking feathers on the Wood Duck flanks look that way because normally hidden sections of them are exposed. Feathers tend to wear and sometimes bleach with age, and often get ragged tips or margins. Ingrowing fresh feathers have much cleaner margins and tips, and often brighter pigmentation. In the Wood Duck photo, one feather high on the right side is brighter blue and appears larger than the surrounding ones. This is a newly-grown feather, with unbleached color and unworn edges. It looks bigger because the feathers that normally cover most of it have molted and have not yet grown back.
If you learn to recognize these features of plumage, recognition that a bird is molting can become almost automatic.
From: "<baro...>" <baro...>
To: "jonathan" <jonathan...>
Cc: "obol" <obol...>
Sent: Saturday, June 27, 2020 7:57:14 AM
Subject: [obol] Re: Wood Duck question