Chicken has bare butt

[jclausen]

All three of my RIR have bold butts. I have attached pic of one of them.
I thought is was molting but did not think that started on the butt area.
By looking at the pics can any one tell what the cause may be?
I have cleaned out the coop and spray pesticide for mites all over inside the coop.
I have also dusted them with

 

[dawg53]

There might be some feather picking going on, so you'll have to observe your birds and watch for the feather picker.
I suspect the primary cause would be urates in feces scalding the skin, causing redness and irritation. Treatment is applying Nu-Stock to the red areas. The Nu-Stock will heal it in no time and will prevent feather picking at the same time.
Nu-Stock can be found in the Equine section in a feed store. Shake the tube well and wear disposable gloves when applying it.