I've written something more about integrating younger chicks than adults, but maybe you can get something out of it that will help. We all do it differently and have different results. Good luck!!!
You'll get different opinions on here because many of us do it different ways. To me, a lot depends on how much room they have and how you manage them. I know it does not help you any, but this is mainly why I am always glad for a hen to go broody. She takes care of this for me. It can be a dangerous time. But yours are not broody raised chicks.
I'll go through a long explanation of the behavior, then tell you some about what I do, but if my circumstances are different from yours, you probably cannot do it like I do it. Hopefully you can pick up something beneficial from my post though.
Part of it depends on your chicken's personality. They are living animals with their own personality. No one can truly predict what an individual chicken will do, but we can tell you what we have observed. You can have different types of aggression. First, you have the pure integration. This is where the two flocks dont all see themselves as one flock. They look at the other chickens as intruders that must be driven away or destroyed. Each flock has its own dynamics. Some flocks are real accepting and some are not. Housing your chickens next to each other for a while will really help avoid this type of aggression.
Some flocks have a chicken that seeks out to destroy any new weaker chicken. Young chicks certainly quality as weaker, but it could be any chicken you add to the flock. Usually this is a hen, not a rooster. My roosters have always protected or ignored the young members of the flock, but that does not mean yours will. Sometimes a rooster may see them as a threat to his flock instead of an addition, but usually it is a hen with the dangerous attitude.
Many flocks do not have chickens that will seek out and destroy a weaker chicken. That does not mean you are safe. There are still the pecking order issues. Maturity has a whole lot to do with the pecking order until they all reach maturity. Mature chickens will dominate immature chickens. Think about it as chicken etiquette. It is bad manners for a chicken lower in the pecking order to invade the personal space of a more dominant chicken. In chicken society, the more dominant chicken has the right and the expectation that they will enforce their dominant rights or lose them. If dominance is clear, the dominant chicken will peck, the less dominant is intimidated and runs away, and everything is again calm and peaceful. If dominance is not settled, they can fight to decide which one is dominant. Sometimes you have the seek-out-and-destroy types who chase the weaker ones. If the weaker has room to run away, this usually does not happen. But if the weaker one does not have room to run away or gets trapped against a fence or in a corner, the dominant one gets indignant and is determined to teach this challenger a lesson, even if the challenger is trying to run away. That is why having enough room is important.
Food, and to a lesser extent water, is another way for a dominant chicken to enforce its dominance. The dominant chickens will often keep the less dominant away from the food, sometimes to the point that the weaker chicken can suffer from malnutrition. I keep two separate feeding stations available anyway, but when I integrate, I add more and make sure they are well separated. Same idea with water.
Bedtime is the time that I have seen mine be the most vicious about enforcing their pecking order-personal space rights. Have plenty of roost space.
I keep my brooder in the coop from day 1. I have a 3' x 5' brooder mainly made out of wire but with a good draft guard and I keep one area in the recommended temperature range. I let the far corners cool off as they will, usually around 20 to 30 degrees cooler than the heated spot. They normally spend most of the first two days under the heat, but after that they play all over, only going back to the heat when they need to. They do sleep under the heat. After they fully feather out, usually around 4 to 5 weeks, I take away the supplemental heat and take them out of the brooder. I then have a space for the adults and the chicks that is separate but where they can see each other. I let the adults free range (no fences so they have a lot of room) but keep the chicks in an enclosure until they are about 8 weeks old. At this time, I figure they are big enough to not be such hawk magnets and start letting them free range. Some people do it at an even younger age. They have separate sleeping areas and do not sleep together.
The chicks very quickly learn to stay away from the adults, but my adults do not go after the chicks. If their personal space if invaded, my hens will peck to enforce their pecking order rights. I've never seen my rooster do that, but he also does not get involved unless an actual fight breaks out. Then he breaks it up. These fights are when the chicks are old enough to try to establish pecking order rights, usually around 15 weeks old for roosters, a bit older for pullets. My younger chicks just try to run away.
I think it is good for them to sleep apart even after they are fully integrated during the day, at least for a while. Mine are more aggressive on the roosts than at any other time. When they do start to sleep in the same coop, for about a week I make it a point to open that pop door real early so they can get away from each other instead of being cooped together in a small space. After about a week, I can stop worrying so much about that. They can normally stay in the coop with the adults without too much danger. The younger ones stay on the roost out of the way and the older ones roam the floor where the food and water is. I have a large coop so the young ones can get away from the older ones, at least to a point.
I think I can do it this way because I have a large coop, a large run, and I let them free range a lot. If your space is tighter, then you might have a real problem doing it this way. I'm also around during the day to watch them, but in reality after I let them out, I don't do much. It just makes me feel better if I am here. I have a fairly laidback flock with a rooster that helps broody hens raise their chicks and hens that ignore the chicks unless personal space is invaded. My circumstances are probably different yours, but hopefully you can pick something useful from all this.
Sometimes it is so easy you wonder why you were worried and sometimes it is a disaster. Good luck!!!
we put some chicks 1 week old with one day old now they are 3 months old n they are very good friends.
