This can be caused from several things,
His diet is dreadful, he should be on a diet of healthy pellets(even a seed diet would be better then what your feeding him and that gives birds organ failure) with fresh veggies, such as kale, broccoli, spinach, and squash.
The cage
Why doesn't he have perches! I don't want to sound mean but he needs somewhere to sit. Sitting on the problem is going to give him severe feet problems which may have already started.
The cage he is in is a poisonous cage, the rust can make him very sick. He actually doesn't look all that well, his feathers are discolored.
He has no toys and no perches and a diet that is going to the death of him, any bird would pluck in that situation.
The best thing you can do for this bird is buy a new cage(rust free and double in size with proper bar spacing so his head can't get stuck) get him proper perches, and either buy him pellets to eat, he'll need to be slowly weened onto them so he gets used to them as well as fed fresh veggies. He is also in desperate need of seeing a avian vet, if you can't afford to get him a new cage with perches and a better diet you need to consider finding him a new home with someone who will, or surrendering him to a parrot rescue.
I'm s sorry this sounds harsh but I want you to understand how bad this birds situation is, even if he's taken out and played with it's not enough
(I hope this isn't a troll post)
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