Amazing Grey

There can be many factors as to "why". First and foremost a detailed Avian Vet check, including bloodwork should be done to rule out any possibilities of other illness, allergy, parasites, or even metal poisoning. 

We can touch base on some of the reasons......

Disease: PDD (Proventricular Dilation Disease) will cause birds to feather pick or Aspergillosis (mold effecting the respiratory) has also been an indicating factor.  

Toxins: Zink poisonings caused from exposure to unsafe metals. Safe metals such as stainless steel are recommended as toy parts/hangers.

Tramatic experience: Children are a big factor in effecting mental health. If a child is not taught respect and caring for any animal this can lead to harassing an animal which can be very tramatic, especially if there is no where this bird can escape from its proceived threat. Physically abusive behaviors used as correction will damage any bird and something they will always remember.

Lack of proper diet/exersize: Inadequate diet will leave the door open to disease and health problems such as allergies (see next one below). Exersize gives an outlet to release tensions and minimize behavior problems. 

Skin infections/hypothyroidism: Cause from allergies to sulfites or micro-organisms found in nuts such as peanuts or other environmental factors. Usually will cause red itchy patches that lead to more picking that can lead into bacterial and fungal infections.

Lack of moisture/baths: Birds may be itchy from the lack of humidity that is essential to good feather production. Daily misting and a good soak once a week will be beneficial. Humidifiers also contribute to added moisture during dry seasons.

Boredom/not enough 'shredder' toys: Birds need toys and activities to do during the day. If they are not present, it will leave the bird nothing to do except to start over-preening which can lead to plucking.

Recent change in environment: Too much stress is a well known factor, birds pick up on our moods.

Inadequate cage placement: Place a cage in a corner or somewhere where they have at least one wall to provide a safe haven. In front of windows may stress a bird from preditors they can see outdoors.

Lack of proper sleep: Birds need 10-12 undisturbed hours of sleep. A cranky bird can get stressed easier, thus plucking. 

Behavior: The more you make a big deal when you see a bird plucking by telling him to "stop" or "oh, you poor baby" you are reinforcing this behavior as preceived attention, thus doing it soley to get your attention again. Best thing to do is ignore until they stop or distract by making a noise like a knock or whistle (while not looking at them), then REWARD when they have stopped by telling him he's a good bird. Placement into a new station (playstand, cage, or boing) and give a toy will change thought process and stimulate activity instead of boredom. Always PRAISE the good and REDIRECT the bad.

As you can see the list can be extensive. I could go into every possibility but have a great link explaining about feather plucking which is very detailed from a medical prospecive. To see more medical/info links, click here to take you to the links page.