Hen missing feathers on her rear, why?

[KatherineNaomi]

One of my hens is missing feathers on her rear, a few inches below her vent. She seems perfectly healthy and happy otherwise. She's the only one of our 12 girls that has this. She had a pretty hard molt last fall and these feathers never really grew back. Any idea why? I've read that mites can cause this but wouldn't it effect the rest of the flock? Any help would be greatly appreciated. Thanks!

 

[Wyorp Rock]

Watch to see if she is being plucked by another hen - sometimes this will happen at night when roosting.

You can cover the redness with a little Blu-Kote or Pick No More.

Some hens do seem to get a bare spot as the season progresses, she may also be rubbing them off getting into/out of the nesting box. Give her a once over for lice/mites, but usually a bald spot is from plucking or having the feathers rubbed off.