It might just be natural skin flaking which they do I tried to see my drakes skin and his feathers are so tight I couldn’t get to his skin. I’ll have to check one of my females. this is interesting since I’ve never really looked that close at their skin.
I only noticed it when she got out of the pool and flapped to dry off. It’s directly between shoulder blades (wing blades?) It’s especially weird because she has no feathers there. I have 2 other girls molting, they don’t have this though,so maybe?