Molting or mites

[4chix]

I have 3 hens and one rooster. The three hens all appear to be losing feathers above their tail feathers. The rooster doesn't appear to be losing any feathers.
Could it be mites or are they just molting. They hens are laying fine and they have lots of room to roam freely.

 

[Cloverleaf Farm]

The rooster is ripping the feathers out / breaking them when he is mating the hens. You can get aprons for the hens to protect their backs from the rooster.