Did you check him over for fleas, mites or lice? Fleas are easy to see, they cluster on the comb and wattles and black dots. But for lice and mites you have to part the feathers to look at the skin.
Lice are usually beige or brown and are big enough to see them moving along the feather shafts. Their eggs look like sticky gray clumps.
Mites show up on the skin itself as clusters of black dots. Every one of those dots is a bloodsucker.
If you find any large grey squishy things filled with blood right where the feather shaft meets the skin, those are red mites and very horrible critters indeed.
Part the feathers to look especially on the back of the neck, the back where the wings fold, and under the wings. Legs too.
If you find anything, let us know. Start treatment right away. Sulfur or permethrin work. If you use permethrin on the bird, make sure you dilute according to instructions. You can find that info online. Concentrations are different in South America, so my formula won't apply. I have a 100% organic fruit farm. I don't like chemicals. But I will use permethrin on my chickens when it's necessary. External parasites are just as dangerous as internal, especially the bloodsuckers.