That parrot is most likely unhappy for some reason. Either it has been taken from it's mate ( they matefor life) or it is very bored or craving more people interaction. or a very remote chance is lacking in vitamin/mineral dept.
It was a rescue. It was abused in it's younger years. The previous owners used to spray it with a water bottle. It started the habit of plucking itself when it lived with it's previous owner. The bird seems happy now and is quite the character, and VERY talkative. It just still has the bad habit of plucking. They have four or five rescues, they keep them in their own very large cages, in a "bird" room (a bedroom designated for the birds). The naked one is so personable, it is the only one they can trust to carry around on their shoulder, or bring outside to sit with them.