Hi... First off, it isn't a meat bird if it is 12 weeks... At 12 weeks that thing should be so heavy and large, and near to death. Might be a Rock though. I agree that it's probably a boy. I also think you have probably learned a very big lesson right now. Never to add just one bird. NEVER. I had chicks that I bought, brooded, and when it was time to go outside, I built another grow out coop for them. I didn't put them in with the established flock. Then they had a run so they could be seen but not hurt. When they hit about 10 weeks, they were allowed to start free ranging. They were near to four months old before any of them started to use the biggest coop, and that's because I had to move them nightly till they got it. Point being, even in small flocks, there is a pecking order. Your new bird comes in alone, he is targetted, and has no companion. Unless the other roo kicks the bucket, or this one kicks his butt, he'll continue to be low roo, and ostrasized. He should have been accepted by now if he was a she. Even the hens will peck on a cockerel who is not their main man. I'd find him a new home with no cockerel/roosters. JMO.
