I have 4 RIR pullets and 2 (i think) Japanese bantams. The RIR stick together and the 2 bantams stick together. if the RIR are in the run the bantams stay up in the roosts of the coop. They very rarely come down and if they do they stay far away from the others. I never see fighting or anything like that, they just stay away. the RIR are about 13 weeks and the bantams are 20 weeks. Is it normal for them to "stay with their own kind"