If the vet determines your bird to be free of psittacine beak and feather disease (PBFD) or other medical problems, then your bird's plucking is most likely due to an environmental issue. (thesprucepets.com)
Back then, we had a full line of psittacines as well as the reptiles. (petbusiness.com)
As a young bird, we worry about infectious diseases (such as Psittacine Beak and Feather Disease (Circovirus), Polyomavirus, etc. or genetic / congenital problems (problems that occur prior to the time the chick is hatched). (drexotic.com)