5 month old rooster plucking feathers off of hens butts for no reason

[FluffyButtHutMama]

My rooster has been randomly going behind unaware hens butts and plucking a mouthful of feathers off! I don't know why and my poor hens take off running! happens more when they're in their run and I want to either completely separate him, maybe cull, or try those little chicken glasses. Please give me guidance.

 

[oldhenlikesdogs]

Feather plucking is generally from a protein deficiency, or boredom and crowding. What are you feeding. What type of set up?