Why so late to attempt integration, did you just get the pullets???
In any event, I routinely integrate less than 2 month old birds with a flock of birds some of which are more than a year old. The process is "see and be seen" and happens over a couple weeks when the birds are separated by netting but can see one another. I make sure both groups have plenty of room, and get fed at the same time in sight of one another, so they don't feel there is food or space competition.
I also have a small PVC and garden netting mobile "cage"? I move around. Somewhere around 10 days, my hatchlings go in it, and it goes in the yard/pasture where adult birds can see them but not touch. By thre eweeks, the hatchlings get moved to a grow out pen and house in the barn. It has some 5' t-posts with green snow fencing strung up. The young birds mostly stay inside, whjile the adult flock free ranges around them. Some of the adults have learned they can jump the fence, but its not been an issue so far. I continue to house the young birds in the barn (mostly so I can ensure they get a higher protein feed at night). By five weeks, I've taken the 4' door down, allowing birds to flow into, and out of, the grow out pen and free range with the adult flock.
at six weeks, I consider them fully integrated. They sleep in one of the adult hen houses in one of the two runs, and the next batch of hatchlings gets moved into the grow out pen.
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