I hatch chicks/keets every year and have to introduce the newbies to an established flock. After I have brooded the chicks/keets for at least four weeks plus to where they are getting feathered in and able to take temperature differences. I have made a "introduction cage" out of a old ferret cage (found on the side of the road with a free sign on it). It's a 3 foot by 4 foot rectangle about 18 inches deep with a hardware cloth bottom standing on wire legs to allow poo to fall down into the deep litter under the cage on the coop floor. It has doors on the top that I use to place the chicks/keets food and water inside, separate from the adult flock. After a week or two of the Adults getting use to seeing the juveniles, I will open a side door wired just enough for the juveniles to exit and enter, but not the Adults---otherwise the hens will enter the cage to eat the chick starter rations. Once I have seen some mixing without stress and violence, I'll remove the intro cage to force the juveniles to blend. The only problem you may have is one I have is that the juveniles are reluctant to join the Adults on the roost and night and may roost in the nestboxes leaving a mess for the egg layers in the morning. Therefore I have a closure for the nestboxes that I kick the juveniles out in the evening when I shut them up, close the boxes, and then open the nests in the morning, forcing the juveniles to either roost with the adults or huddle on the floor until they develop some courage.
