I have 2 pekin ducklings that are way bigger than the Rouen ducklings we just got. I let them all out in the yard when the weather is nice and I watch them as they eat. Well today I noticed that the pekin ducks peck and bite the smaller rouen ducks when they get near the food. They are maybe only a week or two apart so I thought they would assimilate fine. What can I do to make them all get along?