why is my quaker parrot pulling his feathers

I'm going to reference another answer I gave about an African Grey who plucked. This was the answer I had and it might give you a better idea about the issue:

I attended an Aviculture Federation convention last year. One of the speakers was Dr. Susan Clubb who has been doing research on feather plucking. The discovery of subcutaneal bacterial and fungal infections was found to be a major player in many instances of initial plucking. After the initial problem has been addressed, the "habit" of plucking might still remain.

As is the case in just about anything, ruling out a clinical issue is job one.

After that, you have to start working on the diet, and then the environment.

As for the diet: go very heavy on the dark green and dark orange vegetables: broccoli, kale. yams or sweet potatoes, turnip greens, carrots etc.

Get him a vitamin supplement: ProVital makes a good one. A calcium supplement is good as well.

I don't know where you are located in the world, but this link to "The BirdCare Company might be able to help you out with the plucking:

http://www.birdcareco.com/

There is also a technique known as "packing the cage". This simply means putting all kinds of things in his cage that he can play with: branches, wood pieces, anything he seems to prefer to chew, and put a lot of it in there. If your Grey is occupied with playing, climbing, chewing, etc., he is not plucking his feathers. Every minute he is doing something else, is one minute devoted to staying clear of his feathers. The object is to break the habit by keeping him totally absorbed with learning to chew and play with things other than his feathers.