Yellow Crested Cockatoos
Hi Herman,
These birds are almost certainly released captive pet birds. The feather loss is due to feather plucking and I suspect from the pattern of feather loss the 2 birds may well have been cage mates. Feather loss on the chest and wings can be self inflicted, but feather loss on the head and neck is usually caused by overgooming by a cage mate.
Feather plucking in parrots occurs as a result of stress and boredom - these are highly intellegent birds that require a lot of mental stimulation. In cases where there have been prolonged periods of feather plucking (as is likely to be the case with the first bird) the feather folicles become damaged and no longer produce new feathers, if this is the case this bird may be in serious trouble come winter time!
Its shameful that people do not give up their pets through appropriate channels such as SPCA & AFCD where they can be rehomed!
Amanda