While behavior or diet/health plucking is likely.
You are going to need to test for PBFD when you go to the veterinarian. As bald patches on head and face are places he can't pluck. And are very difficult to remove with feet or rubbing......
Please don't self treat for mites unless they are seen or diagnosed by a professional. The medication can be toxic or irritating to birds.
I don't see scale thickening on legs or face. So scaly face and leg mites are unlikely.
The red mite sucks blood. Tho very small, can usually see, or evidence of in un-clean dirty cages, in corners and debres.
Reading Time: 5 minutes We’ve taken an in depth look at the different diseases that affect captive birds in our blog about parrot welfare, and many of these conditions and their symptoms can be extended to budgies, canaries and finches. But one subject we’ve haven’t covered is mites ...
johnstonandjeff.co.uk
www.omlet.us
Excerpt above on red mites
"
Red Mites
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An infestation of red mites (
Dermanyssus gallinae) causes birds great discomfort. The blood-sucking creatures are difficult to spot with the naked eye, at just 1mm max. They are also nocturnal, attacking your pets at night. If unchecked the mites will soon reach plague proportions, and the resulting blood loss may weaken your parrot’s immune system and lead to secondary infections.
One way of verifying the presence of the tiny mites is to put double-sided sticky tape in the nooks, crannies and corners of the aviary where the creatures gather in the daytime. The mites will get stuck on its surface. Once you know they’re there, you need to clean everything in the cage thoroughly with hot water and a scrubbing brush, and keep checking and cleaning over the next few days until they’ve gone"
Also for behavioral. Cage size is important. As well as cage placement. A cage on the floor causes increased stress so raise to your chest hight when standing can help. To small of a cage causes a lot of stress, they can't move around enough, or retreat from stresses. Not enough perch options toys ect.
Chronic zinc toxicity can cause itching and feather plucking. Many cheap toys, cages , food dishes can containvzinc. As well as chains, bells, jewelry, curtain rods...birds.
The presence of other pets especially predator pets like cats , dogs, ferrets, rats , snakes can cause chronic stress.
Diet is important in overall health and immunity. Proper nutrition plays a big role in feather health. A seed only diet is lacking vital nutrients, vitamins and minerals. The diet must include pellets or vegetables or both in addition to seeds. Diet we have tons if threads on. Plus lots of help and guidance if you have a dedicated seed eater who doesn't recognize other stuff as food yet.
Feather plucking/ or feather quality issues are complex. Definitely must start with evaluation with an avian veterinarian to rule out health issues like bacteria, yeast, virus, parasites, toxicity, nutritional deficiency. A look at cage, lifestyle, and diet, and stress.
If behavioral, head feather would be intact unless another parrots were plucking their head. So you really need to rule out health issues.