I'm sorry that your question wasn't answered in a timely manner. We don't have many avian vets on this site. You've asked a straightforward question but the answer is far from straighforward.
Feather damaging behavior directed toward the bird itself is one of the most common and vexing conditions that avian veterinarian can be presented with. The causes for this condition are often multifactorial and cascading in their effects. By the time I see such a bird the original inciting cause may have disappeared or been obscured by other complicating or reinforcing factors. It's important for caretakers to understand that a successful outcome may simply be a reduction rather than elimination of this behavior. Please take your time perusing the following. There's quite a bit of information to absorb. Please return to our conversation with further questions or concerns if you wish. I have to leave my computer for the night but I promise to reply in the morning if need be.
Feather damaging behavior may be due to either physical or behavioral problems and these are not mutually exclusive. Physical causes include the following:
Dermatitis: infectious (bacterial, fungal, viral); chemical (e.g., nicotine absorbed from the caretaker's fingers) or allergic (unproven at this time).
Folliculitis: bacterial, fungal, viral.
Malnutrition: Important; an all-seed diet often results in dry, flaky, skin that is predisposed to superficial infections and pruritis (itchiness). Nutritional imbalances are a common cause of illness in our pet birds. What has Charlie's diet consisted of, please? Seeds should compose less than 20% of his diet. Ideally, a balanced pelleted diet such as can be found here: www.harrisonsbirdfoods.com or here: www.lafeber.com/pet-birds should be fed as well as hard boiled egg yolk, pancakes and cornbread, the tops of fresh greens, dairy products such as yogurt and cheese, fresh fruits such as apples, pears, melon, kiwi, and berries, vegetables such as broccoli, carrots, beets, asparagus, cabbage, sweet potato, and squash, and even tiny pieces of meat.
Environmental conditions: extremes of humidity, aerosol contamination and cigarette smoke.
Heavy metal toxicosis: often incriminated but not proven
Underlying painful lesions: liver pathology, osteomyelitis (bone infection), pancreatic disease, renal disease, neoplasia (cancer), underlying abscesses.
Reproductive activity, perhaps through ovarian and oviductal enlargement and liver changes in females might cause abdominal discomfort and feather damaging behavior of the thighs and ventral abdomen.
Parasites: mites and lice are overdiagnosed; the protozoan Giardia has only been associated with this behavior in cockatiels.
Psychological causes include the following:
Attention seeking behavior: this occurs when a pet uses feather damaging behavior to obtain attention from a caretaker when the caretaker isn't engaged in an activity with the bird.
Anxiety: anxiety disorders may have both biological and/or environmental causes. Improper socialization during the hand-rearing process may be reflected in an inability of such birds to cope with otherwise normal situations due to fear, real or imagined, of a person or situation that the bird is exposed to combined with a lack of self-confidence due to a history of undermining events. An example of this is severe wing clips in juvenile birds that are learning to fly. The resultant heavy falls to the ground may trigger feather damaging behavior. Separation anxiety is another disorder characterized by behavioral signs of distress (screaming, feather disruptive behavior) that occurs when the bird is left alone. These are a distress response to separation from the caretaker to whom the bird is attached.
Boredom: for captive birds with food provided in a dish every day, only 20% of the day is spent foraging and eating while the other 80% is spent socializing and grooming. When socializing opportunities are limited (e.g., the lone bird in a household where everyone is at work during the day), over-grooming may occur and feather damaging behavior results.
Compulsive disorders: compulsive grooming (grooming in excess of that required for its purpose and which interferes with normal behavior) is a good example. It can't be interrupted.
Displacement behaviors secondary to stressors: examples include unwanted exposure or contact with people; this behavior may be accompanied by aggression and fearfulness of humans.
The diagnosis is made through a thorough history which should focus heavily on the bird's interaction with its environment and the people and other animals around it. An avian vet (please see here: http://www.aavac.com.au/) should perform a detailed physical exam including diagnostics in the form of blood and urine tests and whole body X-rays. Skin biopsy, pathogen detection through cultures or PCR (DNA-based testing) may be recommended.
If a physical cause is unable to be determined and the patient's history supports it, a diagnosis of behavioral feather damaging can then be made. At this stage a specialist veterinary behaviorist should be considered. In general, the following is true when the timing and nature of feather damaging behavior ...
...occurs when caretaker is not present - separation anxiety and boredom should be considered.
...occurs when caretaker is present but not paying attention to the bird - attention seeking behavior should be considered.
...occurs when the bird interrupts other behavior to damage feathers - obsessive/compulsive disorder or true pruritis should be considered.
...occurs when the bird exhibits signs of unwarranted fear - anxiety or stress of generalized anxiety disorders should be considered.
...starts at an extremely young age; handfed bird - improper preening or poor early socialization should be considered.
...causes frayed and splintered feathers - suggests anxiety disorder, improper wing trim, feather trauma due to small cage.
...is seen in an overly bonded, sexually mature bird that displays sexual behaviors out of context - reproductively related.
Elizabethan collars are rarely indicated unless self-mutilation and/or physical trauma is occurring (it is). Restraints may worsen the patient's anxiety state and aggravate the original problem.
Psychotherapeutic drugs may be of benefit. These include benzodiazepines (e.g., diazepam/Valium, haloperidol, tricyclic antidepressants such as clomipramine, SSRIs such as fluoxetine (Prozac). All are available through an avian vet. Applying ointments such as Imflamol (which contains two antibiotics, a glucocorticosteroid, an antifungal drug, allantoin, and vitamin A) should be avoided. Charlie's going to ingest those drugs while preening.
It must be ensured that stability and security are present in the bird's lifestyle at home. Anxiety disorders arising from fear of human interaction or fear of falling due to an inappropriate wing trim can lead to feather damaging behaviors. Triggering events that may have had a role in the development of feather damaging behavior such as changes in the household or a perceived lack of attention should be identified. Basic training is implemented and strengthened using a system of positive reinforcement. Once this has been achieved, training can be extended to guide more normal behaviors. 80% of the bird's day should be spent foraging for food, the remaining 20% on grooming and socializing activities. In practical terms this can be done by:
Providing foraging activities both with and without the caretaker being present. The bird may need to be taught how to participate in these activities as at first it might be afraid of new objects or activities.
Enhancing "normal" feather care through gentle misting with water and by providing other items that can be groomed in addition to the bird's feathers.
Developing more normal flock and social interaction. It's important to remember that it's essential to replace unwanted behaviors with more desirable behaviors; at no time should a behavioral void develop through removing an activity or interaction without replacing it with others.
Regular communication and follow-up evaluations with the avian vet and/or behaviorist are important. If the result is a healthy, well socialized bird that actively engages its environment and its human companions, the state of its plumage becomes less significant.
Thank you to Dr. Bob Doneley at the University of Queensland, Australia, for an excellent synopsis of this behavior which I freely excerpted here.
Please respond with further questions or concerns if you wish.