I have 6 chickens and 3 ducks in my original flock and they are 18wks. About a month ago I added 7 more which were about 3 wks old. I free range them in my back yard which is surrounded with a privacy fence. I kept the babies separate at first and have slowly introduced them to the older flock and I expected them to give them a hard time at first but a month later they are still being picked at. I continue to keep them separate at night but during the day they run the yard but constantly have to run for shelter to escape the older ones picking at them. Is this common or will this eventually pass? Does it make a difference that they are different breeds?