I have some 3 week old RIRs (26). I just moved them into an open air coop (dog kennel fence with adjustments) about 3 days ago. I also got 5 White Creasted ducks and 5 Mallard Ducks. As I was off work yesterday I wanted to see if they would get along still being young. I put the ducks in with the chicks and sat in there with them and just watched.... It was free run at first until about 5 minutes passed and soon all the ducks where stuck in one corner of the fence/coop. everytime one of the ducks ran for the food, one or two of the chicks would run them back in there corner. It was funny as the Mallards were a bit more challenging and kept trying there luck. But I learned real fast that they would probably starve to death if I left them together so....Back to building a seperate coop for the ducks !