Birds can suffer from psychological issues just like humans can.  These issues can vary from anxiety disorders to self-mutilation syndromes.  Feather destructive behaviour (feather plucking) is one of the most common presentations.  Separation Anxiety is another.

Mel Vincent has an amazing track record for solving psychological cases.  She works closely with avian vets and can ensure that both a medical and a behavioural plan are in place to treat your bird.

Successful treatment for these cases is a lot more complicated than simply adding foraging/enrichment.  It is essential you see a qualified behaviourist with a psychology background to treat conditions like feather plucking.  You need a well formulated behaviour modification plan for your bird.