Vitamin C
Vitamin C deficiency has been directly linked to feather-destructive behaviors such as over-preening, barbering or chewing the ends off the feathers, plucking and self-mutilation. If your bird exhibits any of these behaviors, his environment should be evaluated in addition to his diet to ensure they aren't being caused by boredom, tiredness, or another underlying medical issue. Natural sources of vitamin C include broccoli, cherries, guava, kiwi and peppers including red, sweet and bell. When adding fresh fruits and vegetables to your bird's diet remember to limit them to 10 percent to 15 percent of his total diet.