Am 95% sure it is one of the girls pecking (have 4 one has a damaged beak and wouldn't be able to but has intact butt feathers, two others have bald butts, so elimination would suggest it's the 4th). Plus, although one of the baldy butts is moulting, there is not a trace of a feather anywhere.
Some recommend clips some recommend trimming the very tip of the top beak to stop the tweezer action (the beak with the damaged beak has this over trimmed as a chick and never grew back). The person recommending this says it will grow back but by the time it does the chicken should be 'cured' and says that clips are cruel coz they fit in the nostrils.
Any advice? Also, what can I do in the mean time to soothe poor red bottoms?