My favorite chicken, an Americauna, is missing feathers at the base of her tail. Rather, it looks like the feathers may be broken off? Once, my Buff Orp. had the same thing, and they all of a sudden grew back in the last few months after having looked horrible for almost an entire year. What is this? At first I treated the Orp with all kinds of sprays and treatments for mites- but nothing worked. So, I'm curious to see what other people say it is- and whether or not I should be treating it?