You need to actually see the mites themselves.What are the symptoms of red mite?
And what is the best way to sort it out?
Very indicative of over mating... not enough ladies for that young of a stag, or maybe he has favorites. Sometimes the hens might have more brittle feather quality causing this type of damage... but putting your boy on a tether so ladies can approach as they want could be one option. I keep my stags separate until they gain some maturity. Some people use saddles or aprons while some people say that causes hens to over heat.