I had 9 birds that all grew up together and are between 6-7 months old now. I got 4 seramas about two months ago. I guarantined them for 3 weeks, than put them in their own pen inside the bigger pen so that everyone could get used to each other without touching each other. Did that for several weeks, then I allowed them to mix with each other. All the bigger birds seem fine with them except one pullet that stalks them and chases them as soon as she sees them. Any suggestions on solving this problem will be appreciated.