Then this is called barbering, when a bird just shreds their feathers. It could be happening for a variety of reasons. Though it's good to point out that barbering does not always mean your bird will then start fully plucking. We have a barbering bird that has never progressed to plucking as well as a plucking bird that also barbered all her remaining feathers to death. So it can go either way.
For now I would try to figure out why the barbering is happening. Could be anything from a simple desire to chew (in which you would want to provide lots and lots of shreddable toys), to over-aggressive preening (from stress? an unfortunate learned habit?), to allergies if his skin is feeling aggravated. I would try a vet visit to rule out anything internal then look to his environment. Hopefully some little changes will be all you need to clear things up!