Losing feathers on back & vent

[SgtPepper]

One of my Plymouth Rock Black & Whites has a bare spot on her back and vent. I thought she might be moulting or maybe from our roo, but she's not losing feathers any where else and we had to give the roo away a few weeks ago because he was getting too aggressive and she's not getting better. She is eating normally and laying eggs but she is at the bottom of the pecking order - seems the RI Reds have taken over since the roo left. I don't see them attacking her, though they will push her out of the way or peck her when she tries to eat out of the same dish.

I have pictures, but the site won't let me post any because I'm new.

 

[SgtPepper]

Here we go...

 

[lanie8]

I'm not an expert because i've only had chicks for a few weeks,but can mites,or lice cause feathers to go missing?

 

[SgtPepper]

I don't know. I've only had them for a little over a year and haven't seen this happen before.