I hope you don't mind a follow-up question on this topic - and about a macaw . . .
I had the exact same question. Apologies for the "wrong" bird for the forum . . . I was exploring in my mind the idea of a cockatoo & got caught up in the discussions.
My Greenwing was placed with us in January because he had become worried in his former home & had begun to pluck. He is still looking a little moth-eaten. He has pins, so I know he is molting, but I think he is still plucking. Sometimes I tell my husband, "Goose is in a mood today." and often, the next day, there is a large flight feather or tail feather on the floor.
I also see fluffies & "regular" feathers on the floor.
The ends of the larger feathers are crushed, as is the middle of the feather. The middle from him holding it in his foot & the end from him chewing on it & sucking on the shaft. Often the small-to-medium feathers have a "V" in the end where I believe his beak has nipped out a piece while pulling the feather out. Some of the medium & small feathers are in perfect shape.
He has no completely bald spots, he does not pluck the pins (and he does not want ME to help with them either, thank you very much). And I have not found a feather with blood on the end.
So I can't tell if he is "helping" the feathers molt, or plucking.
Also, he was in his other house from 1 month of age to 20 years. He has been here only since January & so is really still in an adjustment period. [For what it is worth, his diet includes a combination of fruits, veggies, greens, eggs, mash, Harrison's & TOPs pellets & nutriberries, nuts (mostly in the shell) & some seeds. He is quite a good eater.]
Anyone who can help me figure it out by the description, I'd love the help.