Hi Ron, There are so many variables and so many reasons, have you tried the mytoos.com message board for answers? This is a really good site with a lot of caring humans willing to give advice. I'm a mother to a sulphur crested 'too and we've been working with the biting issue here also. Also check with your avian vet to find a local expert who can work with you and your bird. Cockatoos take a great deal of patience and understanding, but the rewards are amazing! I wish you luck. Kris