Chicken missing feathers on her back

[pdw]

I Have a jersey giant who every year starts missing feathers on her saddle. I have 6 chickens and she is the only one with this problem.
I don't have a rooster so that's not an issue .
She doesn't get picked on by the other girls .
I do notice that in the egg box it's always black feathers in the box . Chickens Will pluck feathers when in the egg box .
If all the girls had feather issues I would suspect mites or some pest problem. I keep a clean coop and egg boxes and even sprinkle DE in the egg box along with marigolds . Anyone else come across this issue ??

 

[aart]

I find breast feathers in the nest, but not saddle feathers.
Post a pic of the bare back?
Maybe she just has weak feathers that are easily broken when pecked at?

Always good to do a regular.....
Bug Check:
Have you checked them over real well for mites and/or lice?

Google images of lice/mites and their eggs before the inspection so you'll know what you're looking for.

Part the feathers right down to the skin around vent, head/neck and under wings.

Best done well after dark with a strong flashlight/headlight, easier to 'catch' bird and also to check for the mites that live in structure and only come out at night to feed off roosting birds.

Wipe a white paper towel along the underside of roost to look for red smears(smashed well fed mites).

Good post about mite ID by Lady McCamley:
https://www.backyardchickens.com/threads/my-chicken-has-mites-now-what.1273674/page-2#post-20483008