Wing feathers are being pecked but i dont know by who!

[LaurasNew]

I only have 8 chickens, 3 orpingtons are just 8 weeks old and still sleeping in a nesting box with their brahma Mam. The other 4 sleep in a shed with loads of roosting space. They get 20% protein feed and crushed oyster shell plus fruit,veg and seeds for treats. One of the hens is having her wing feathers plucked while on the roost. I never see anything happening to her during the day. I've tried anti peck spray and alamycin/blue cote but no joy. I don't really want to seperate her if I can avoid it. Thanks in advance for any advice

 

[coach723]

Can you post some pictures of the bird in question?

 

[Esc_Quaily]

Is ot possible to set up some form of CCTV?