Stress may be an issue, but to help him out, a more precise diagnosis is required. Feather damaging behavior can be caused by a multitude of things, including bacterial skin infection,viruses, fungal infections, allergies, metal poisoning, hormonal flux, psychological or combinations of these factors. The difficulty is diagnosing the problems and assigning an intelligent treatment plan. Your vet will want to run a number of tests so that appropriate medications can be prescribed.
If he is not going to a vet that does a lot of birds, he needs to get to an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment. Check the link http://www.aav.org/association/index.php?content=activeMembersList
for members of AAV in your area or call your regular vet and see who they recommend.
Pet/feed store medications are harmful, ineffective, immuno-suppressive, and make them much worse and may interfere with the veterinarian's diagnosis and treatment. Do not use them.
Here are some things that will help before, during and after any treatments:
Birds should be on a high-quality, preferably prescription, pelleted diet. In addition, they should be offered dark leafy greens, cooked sweet potatoes, yams, squash, pumpkin; entire (tops and bottoms) fresh carrots and so forth. No seeds (and that means a mix, or millet, or sprays, etc etc.) and only healthy, low-fat high fiber people food. A dietary change should be closely monitored and supervised by your avian vet.
Birds should get 12-14 hours dark, quiet, uninterrupted sleep at night. Any less and they can suffer from sleep deprivation and associated illnesses. They should be covered or their cage placed in a dark room that is not used after they go to bed.
A daily shower with you in the shower, a bath-bowl or squirter with fresh clean water is a good idea.
The cage material should be cleaned everyday, and twice a day if the bird is really messy. Paper towels, newspaper, bath towels are ok. Never use corn cob, sawdust, wood chips, or walnut shell.