Tell us more about you your bird. What kind of parrot? How old? How long have you had him? Diet? Behavior? Last time he melted? Any other birds? The more information the better we can help.
Lack of Vitamin A and D are the most common causes for poor feather health. Make sure he's eating a variety of fresh vegetables daily and spending regular time in the sun (I understand that you might not be able to take him outside, but try to do it if the opportunity arises).
I am guessing here, but reading around, I think some type of feather eating mite, check out the link below. Even though its chickens being discussed the damage looks similar. In any case a trip to your Certified Avian Vet is in order here. I would not trust this to a regular dog/cat vet.
Hi everyone, I'm at my wits end with this problem which has now spread to a number of birds. Basically something is eating away the feathers in dead-straight lines just as if you've taken a pair of scissors and cut a chunk out. Some feathers are worse than others but its now visible from a...