Can anyone tell me what might be wrong with this hen?

[rooster-red]

Looks more like the work of mites or lice than feather picking.

Check the base of the feather shafts for little white clusters of mite eggs, they will also eat the feathers from the base upward.

Hope you didn't put these chickens in with an existing flock without quarantining them, the whole flock will be exposed.

 

[ChooksinIowa]

I would check out this previous thread. See the pictures on the first page of posts. They did a little surgery on her and she was fine. She was later killed by a dog, but that is not relevant to the health issue. That is why the thread is locked, though. Anyway, it looks like yours is not as bad as hers, but still reminded me of that thread.

https://www.backyardchickens.com/forum/viewtopic.php?id=86999

 

[RoxyOtis]

Quote:
I thought it resembled this also but not so severe...

 

[doodledoo]

Thanks everyone - there were a total of 12 BR and 7 RIR. The RIR were in a seperate pen and they all look pretty good it is the BR that look this way. They all have at least half of their feathers missing with signs of new ones coming in but none of their backsides are red and enlarged like this one.