In Huey's case, he's been doped by a vet for 10 years. Supposedly he is bi-polar which is why they put him on haloperidol. I don't fault his former owner as the guy wants the best for Huey, which is why he re-homed him to us. I almost bought into the diagnosis as Huey does start to act very strange once off his meds. What helped me to realize what was going on, our Caique started plucking over the same period that Huey went berzerk on us. Then they both stopped their respective behaviors at nearly the same time. I knew at that point I had two over-horney boys on my hands. Now the vet not knowing this, is kind of inexcusable in my opinion. They should know that raging hormones can cause this type of stuff and not just throw meds at a bird indefinitely.
Also, he doesn't barber, he literally will chew his feet until they bleed, removing the scales and skin. It's terrible what he does. So far he doesn't do anything to his feathers.