I suspect that the problem is behavioral in nature. The two macaws I have that pick their feathers are both nearing or are at sexual maturity. They both had been hand raised and hand fed from day one.
They were both pets for their first 4 years. The Scarlet Macaw was picked when I bought her and the Greenwing Macaw was fine until I put them into a breeding situation. Perhaps the stress and new demands on behavior caused them to express their stress in a physical way by picking at their feathers. They have little control over anything else. They can’t change their location, go and find different food, or get away from a bird they don’t like. Or get closer to a bird they do like for that matter.
They crave my attention and perhaps they prefer me over their cage mate. And I leave them alone for the most part, so they will transfer that bond to their cage mate. They haven’t laid eggs yet. The haven’t bonded with their mates yet either. They co-exist OK with their cage mate but that acceptance of the male as their mate hasn’t happened. With my Scarlet Macaw, the female has taken to picking the male too. Its not pretty but otherwise they’re healthy.
I started to give them baths, spraying a mist of water over them on a daily basis. I also put St. John’s Wort, a herbal supplement thought to elevate mood, in their feed. Four months later both Macaws were on their way to looking better and having feathers again.
There’s other things to try as well. Change the location of the cage so they have a different view. Or put up dividers to block their view of other birds. Changing how long the lights are on (if indoors) can make a difference too. Macaws equate the length of time the light is on with the season, shorter days mean fall and winter. Increasing days mean spring going into summer.
The main thing to remember is when a parrot does something you don’t want, watch the bird, try to understand what’s bugging them and then try changing something and see if you make a difference. If the change you make works then great, if not then try something else. Behaviors rarely change by themselves – they are usually in response to something new in their lives.