It is very frequent on the site that someone will post concerning difficulties associated with merging flocks and having one abusing other, especially of one of the flocks is made up of juveniles or chicks. I merge flocks almost routinely and have a method that greatly reduces trauma on the smaller birds. Nearly half of my birds are games which makes so they have greater potential for being problematic so if works with them process can be considered to be robust enough to work with most breeds. When merger is to occur in in a confined area such as a run or coop, it is never the smaller birds to be moved in with the larger birds. I always have the younger birds operating on their home turf at the time of the merger. The younger birds are allowed to have at least a week in the coop before larger birds are introduced. When the larger birds come in they will still pick on the smaller birds to assert dominance but they will not feel confident enough to chase smaller birds about causing damage. Making introduction late in evening also makes so birds can get used to each other voices over course of night further reducing social strife to occur the following morning. If birds are of similar size, then make so all are introduced into a third novel location just before dark. Again no one will be operating on home turf so aggression will not be so extreme. Numbers from each flock need not be equal. I always make certain to observe birds early during morning following introduction to make certain no social problems develope.