A broody hen does not wait to wean her chicks until they are the same size as the others. I don’t either. Often, you will find that a bantam will be higher in the pecking order than a full sized chicken when they reach maturity. It is more the spirit of the chicken than the size.
There are three different types of aggression you need to be aware of when you integrate. If you have two or more roosters in the two flocks, they will determine which one is dominant. Sometimes that is a fight to the death or one gets injured in these fights, but often they reach an accommodation and work well together in protecting the flock. If they are not both mature enough to know they are roosters, this won’t happen immediately.
Then you have the territorial type of aggression. Chickens will sometimes protect their territory from strangers. This does not always happen and surprisingly it is usually a hen that does this instead of a rooster. Some chickens, when they see strangers, will try to run them off or kill them. A lot of times this does not happen, but it can be deadly. This is where housing them side by side for a while comes in real handy. They get used to each other and recognize each other’s right to exist. So you probably won’t see this.
Then the one you are practically guaranteed to see. They have to determine a pecking order. Occasionally this goes so smoothly you wonder what all the worry was about, but there is practically always something. Mature chickens are higher in the pecking order than immature chickens. That is just the way it is. You’ll notice I mentioned maturity, not age. I’ve had some at 15 weeks that could establish a position in the pecking order, but that is pretty rare. I’ve had some twice that age that still had not managed, but most manage before that.
If a chicken lower in the pecking order invades the personal space of one higher, the higher has the right and almost the expectation to put that lower ranked chicken in its place, especially if there is a maturity difference. What normally happens is that the mature chicken pecks the immature chicken and the immature chicken runs away. Order has been reestablished. You’ll find that the younger chickens quickly learn to stay as far from the older chickens as they can manage. Occasionally you will get a brute of a hen that goes after the young ones, but that does not happen all the time. I hardly ever see anything like that.
One of the things you can do to help is give the young ones as much of a chance to get away and stay away as you can. Give them as much room as you can. Put in extra perches for them to stay on so they are out of the way. Or give them something to hide under or behind. But mainly give them as much space as you can. For some people with smaller set-ups, this is not easy.
Something else is to set up different feeding and drinking stations. One area of conflict is the feeders and waterers. As part of the intimidation of maintaining their advantage, more mature chickens will sometimes guard the feeder and waterer to keep the younger away.
Something that I’ve seen several times with broodies that might help you understand. I’ve seen chicks maybe two week sold leave Mama’s protection and stand beside other hens at the feeder. Sometimes the other hens ignore the chicks, at least for a while. But usually one will peck the chick to remind it that it is bad chicken etiquette for an inferior to eat with its betters. The chick runs back to Mama as fast as its little legs can carry it. Mama ignores this behavior. The other hen had a right to discipline the chick. Now if the other hen comes after the chick, Mama takes an entirely different attitude and protects her baby. The point is that some pecking is normal and not a cause for concern, but occasionally it gets to be a bit more serious.
Hope this helps a bit. Good luck!!
