Araucana, Americauna, Easter Egger

[Ol Grey Mare]

any suggestions on what it might be? Should I throw in some diatamatous earth or garden dust? we have only had chickens for less than a year but I have one coop with my laying hens (they get let loose to run the farm ever day) only one of them has a bare back - think she is my rooster's favorite. She has been like that for a long time and none of the others do.

So you are certain the top bird (with the bare back) is a hen - meaning you are actively getting eggs from that bird? Are these birds the only birds you have in your flock? If so, and IF you are certain of her gender you are VERY rooster heavy and rooster damage makes sense - I would suggest a "hen saddle" to protect her now exposed skin, not only from the rooster(s) but from the sun, etc- her feathering will come back in after her next molt. A good roo to hen ratio is important to minimize the risk of overbreeding and rooster damage, but even then you can still have a favorite or two who get too much attention and it may become necessary to take steps to separate them or, at the very least, provide protection with the use of saddles, etc if you simply *must* have that hen bred by that rooster.
If this is in fact your entire flock and she is the only female you must separate her from the boys and not re-integrate things until you have lowered your roo count and acquired some additional females to take the attention off this poor girl.

 

[New Chick2]

So you are certain the top bird (with the bare back) is a hen - meaning you are actively getting eggs from that bird?   Are these birds the only birds you have in your flock?  If so, and IF you are certain of her gender you are VERY rooster heavy and rooster damage makes sense - I would suggest a "hen saddle" to protect her now exposed skin, not only from the rooster(s) but from the sun, etc-  her feathering will come back in after her next molt.  A good roo to hen ratio is important to minimize the risk of overbreeding and rooster damage, but even then you can still have a favorite or two who get too much attention and it may become necessary to take steps to separate them or, at the very least, provide protection with the use of saddles, etc if you simply *must* have that hen bred by that rooster.
If this is in fact your entire flock and she is the only female you must separate her from the boys and not re-integrate things until you have lowered your roo count and acquired some additional females to take the attention off this poor girl.

OH NO! That is not what I meant at all! This is a whole separate flock, they don't mix at all. I will try to add a couple more photos

 

[New Chick2]

I have 6 actively laying hens and one rooster plus 11 juvenile birds in an old grain bin that has been converted into a coop. Those are the ones that get let out each day and where my one naked backed girl is. The others, (I call them the araucanas because that is what the hatchery sent them as but I am sure they certainly are not all) in a tractor with a covered kennel attached. The tractor in the pic is of our cx before we processed them.

 

[Chris09]

All the EE's in the first set of pictures look like roosters to me, as for the bare backs that are on all of them. I would say that you might have a might/lice problem. You can dust them with poultry dust, I wouldn't use diatomaceous earth there are a lots of controversy on if it really works or not.

ETA--
It also looks like some of your younger birds are starting to get bare backs also..

 

[New Chick2]

All the EE's in the first set of pictures look like roosters to me, as for the bare backs that are on all of them. I would say that you might have a might/lice problem. You can dust them with poultry dust, I wouldn't use diatomaceous earth there are a lots of controversy on if it really works or not.

ETA--
It also looks like some of your younger birds are starting to get bare backs also.. 

Those are the same birds at a younger age
My juvenile birds have never looked like that. I will run over to TSC now to get some poultry dust. Thanks.