Often, external parasites are not the major contributing factor that we think they are, and can be easily treated with a mite spray.

Chewing and self mutilation of feathers needs to be distinguished from normal grooming and feather sheath removal from growing feathers.  Chewed feathers often have an irregular, ragged look and are confined to areas that a bird can reach (wing and chest feathers, primarily.)

 When the diet is very deficient, feather pickers often pull the feathers and eat the blood-filled tips.

Psychological causes, such as fear, boredom, a change in the household, or lack of sleep because of household lights being left on are a major cause of feather picking problems.  Some birds develop an excessive attachment to one person and will self-mutilate when that relationship is disrupted.

A mixture of one-half mouthwash and one-half water sprayed on affected areas can sometimes discourage a pet bird from habitual picking.

Providing toys, branches to chew and placing the cage at chest height, to reduce stress, can all help with some cases.  Other cases may need anti-anxiety drugs, but the results can be unpredictable.

However, excessive biting, preening, or scratching at one particular area warrants investigation in case the bird has a tumor, abscess, wound or hernia.