I open the coop and the pen door first thing in the morning usually around 6:30 a.m. but when I have to be away I put them all in the pen but one cockerel and 1-3 chickens escape with him.
So you put them in the run when not home? Likely they would fly out if inclined.He's been grabbing them on the neck with his beak and twisting. I've not sure if this is Klingon love play or agregious domination. They squawk and try to get away from him. (Just not ready yet? hate him?)
You have a nice set-up, if they can roam most of the day, then you may be o.k. with your run space.
I would suggest that you may want to add more ventilation in your coop if you are shutting that up at night so you have a good air flow. Even in winter you want plenty of fresh air coming in above - not directly on the birds.
Oh you are right on both counts there LOL Klingon love play and domination.
Yes, pullets the same age just are not ready. Cockerels can be a pain. Even mature hens sometimes are squawkers they can sound very dramatic.
The pullets don't really hate him, they are more confused I think at this point, but if he's really rough, then they may not fight advances when they are older.
There really is a big difference between cockerels and roosters - in actions and courting.
I've done it too, had a cockerel with pullets and it was quite dramatic I must say. Now I usually house the fella next to the hens and pullets, let them see one another of course, but he doesn't get to mingle until at least 8-9 months of age. I evaluate how the interactions go, if I don't think he's ready, then pull him and wait a couple of more months. Others may do things differently, but the older the fella, the better it seems for my situation.