Feather plucking is quite a common problem, especially with young Lutino Cockatiels. Feather plucking usually starts to happen when the chick begins to feather up, and then one or both of its parents pluck out its feathers. The plucking normally takes place first at the back of the neck, but this often happens over a wider area of the body too.
The experts say it is because the adult birds may be keen to breed again, and this is their way to drive their young from the nest box. When these feather plucking mutilations occur, they normally happen within a few hours, so it is difficult to take effective action in time. Feather plucking can be an inherited thing.
If you know that a particular pair of cockatiels are prone to doing this, you can take precautions to prevent a recurrence. Try sprinkling powdered aloes around the necks of the young each day as they begin to feather up. This is bitter tasting and will hopefully deter the adult birds from feather plucking. The other thing to do is to leave a second nesting box close to the first, and then hopefully the breeding pair will just move into the new one for the next batch of egg laying, rather than persecute their existing chicks.
Once the chicks have left the nest the feather growth will return to normal. There is rarely a re-occurrence of feather plucking once the birds have left the nest.
Unlike cockatoos, adult cockatiels rarely pluck their own feathers. If they do they could be suffering from Giardia, which is a parasitic condition which triggers severe skin irritation. If this is the case, successful treatment of Giardia will solve the feather plucking problems.