Red Bottoms

[Clare Pickles]

One of my Hens has a really red bottom. We got them around 2 months ago and they are ex-batts and when we got them their bottoms were red, all the others are fine now except one, does anyone know why this is please?
Clare

 

[Isaac 0]

Can you post a picture?

 

[Kiki]

Pics are great.
Have you checked them at night for mites?
Have you been able to sit and watch them for a while to see if they are pecking each other?