Severe macaw (Ara severus) with bad looking feathers, 2019-08-04

My guess would be that this is not a disease, but is self-inflicted. The tougher feathers which are harder to pull out, and those out of reach, are apparently not affected. So far as I know, wild birds don't do this, so it must be the result of bad captive management (in the past?); presumably the habit once picked up is hard to break - but I must defer to others for more information.