Unfortunately, there is no easy answer to your question.
There are dozens of medical and non-medical causes for feather picking. Medical causes include malnutrition and vitamin deficiencies, an all seed diet, changes in hormone levels, inappropriate humidity, inadequate temperature, i.e.: inadequate husbandry, trauma, internal and external parasites, bacterial and fungal infection of the skin or hair follicles, allergies or hypersensitivities to food and food components such as food additives, food coloring, and environmental allergies: such as seasonal allergies: pollens, grasses, molds, dust mites; airborne pollutants, cigarette, cigar, or smoke from wood stoves, and many others.
The non-medical or stress related causes for feather picking include loneliness (if they are solitary), and the inability to perform mating rituals, excess noise, presence of dogs and cats (the birds view as a potential prey to these mammals), changes in the environment, and many others.
If the feather picking is just in one location it can be the result or an unknown traumatic injury.
I highly recommend that your bird be examined by an Avian veterinarian. Please bring a sample of fresh droppings to your vet to be analysed for internal parasites.
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