Wikipedia
Feather-plucking, sometimes termed feather-picking, feather damaging behaviour or pterotillomania, is a maladaptive, behavioural disorder commonly seen in captive birds which chew, bite or pluck their own feathers with their beak, resulting in damage to the feathers and occasionally the skin. It is especially common among Psittaciformes, with an estimated 10% of captive parrots exhibiting the disorder. The areas of the body that are mainly pecked or plucked are the more accessible regions such as the neck, chest, flank, inner thigh and ventral wing area. Contour and down feathers are generally identified as the main target, although in some cases, tail and flight feathers are affected. Although feather-plucking shares characteristics with feather pecking commonly seen in commercial poultry, the two behaviours are currently considered to be distinct as in the latter, the birds peck at and pull out the feathers of other individuals.
Feather-plucking has characteristics that are similar to trichotillomania, an impulse control disorder in humans, and hair-pulling which has been reported in mice, guinea pigs, rabbits, sheep and muskox, dogs and cats, leading to suggestions for a comparative psychology approach to alleviating these problems.