Hi, I'm Dr. Hannon. I'll be assisting you this evening. Can you upload a picture of the area in question? Typically birds that have feather damaging behaviors aren't able to pluck the feathers on their own head, although some birds (usually eclectus parrots) will rub their heads to the point that the feathers are damaged or missing. If there's another bird in the cage, then it could be overly aggressive allopreening. A third possibility would be some sort of medical disorder, like dermatitis, external parasites, a thermal burn, or even circovirus infection (PBFD). Once you upload a picture, I may be able to give you more information.
From the looks of it, I think that you might be dealing with a sinus infection on the right side. If birds get dried mucus on their feathers, it clumps them and makes the much easier to remove. Also, the main area of feather loss under the eye is right where the infraorbital sinus resides. This sinus can easily get impacted and become painful, causing the bird to rub the area. It would be a good idea to take him to a qualified avian veterinarian. You can find one near you at aav.org.
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