There will always be some picking and chasing of new birds unless they have been exposed to each other quite a bit through the wire on the pen. I have two flocks - one established older flock, and a flock of new birds about 13 weeks old now. I raised the new chicks in the chicken tractor (the older hens visited through the wire) and I started free ranging them about 4 weeks ago. The older flock pretty much ignored them unless they happened to be at the food and water stations at the same time. The older girls asserted their right to be there first and the younger ones pretty much stayed away until they were finished. Now, after a few weeks of being out together, they are starting to roost with the big girls and to forage with them, and the big girls are allowing it. I've not had any bloodshed, but have seen some of the hens biting some of the more impertinent chicks to teach them some manners.
You might see if you can make a way for the new bird to be separated, but still in with the other birds. For example, let them range together, but give him different place to sleep (put hens in coop and him in the run or vice versa). I'd do this for a few weeks then put them in together and see what's happening. Also, if it's a rooster, he's going to have to prove himself to the ladies before they cooperate with his mating instincts. It's kind of funny to watch, but he'll eventually dominate once he gets older.
You might see if you can make a way for the new bird to be separated, but still in with the other birds. For example, let them range together, but give him different place to sleep (put hens in coop and him in the run or vice versa). I'd do this for a few weeks then put them in together and see what's happening. Also, if it's a rooster, he's going to have to prove himself to the ladies before they cooperate with his mating instincts. It's kind of funny to watch, but he'll eventually dominate once he gets older.
