open patch on back without feather

[mondana]

My chicken has a patch on her back that is without feather. Once I happen to see that another chicken has jumped on top of this chicken. She jumped down and I did not see anything else.
Does any one know why? And how I would fix this situation. I do not wish this patch gets irritated and becomes a wound.

 

[Eggcessive]

Many hens will pull out feathers of other chickens with pecking order disputes. Some will do this from overcrowding, a desire to eat feathers if they are not getting enough protein (at least 16-20% in feed,) and if a rooster is present, they may over breed or pull out neck feathers. I would spread some time with them sitting in a chair, and observe behavior to decide what to do. If one is a bully, she might need to be separated for a few days to lower her in the pecking order.