I have 6 RIR hens about 3 mos old. Someone gave me a young roo about 5-6 mos old. He was red with green tail feathers. Within a couple days he bit a hole in the back of the neck one of the hens. Of course the other hens joined in the pecking. I isolated the injured bird, got it healed up and tried to reintroduce her to the flock, free ranging at the time. The roo immediately chased her off into the woods and I rescued her before he hurt her again. I waited a few more days, tried to put her back with the flock free ranging. Same results. Now the roo is gone (with help) and the 6 hens are getting along just fine. I thought maybe this one hen might be a roo simply because the way the mature roo went after her (him?) Anybody have any ideas why this happened? I've never experienced anything like this in the 20 yrs I've kept layers.