There are many factors which can contribute to a feather plucking problem.
Most experts agree that stress is usually one of the contributing factors.
Diet is often another contributing factor. Boredom can play a part, resulting from lack of attention or play time. One easy way to determine this is to check to see if the head or neck feathers are involved. If they are, then the problem is probably physical. In these cases, an avian veterinarian should be consulted.