Well, I've only had ducks for one year now. I have one of each. But the hen is a Rouen, and the drake is a Pekin. He is honestly too much for her alone. The feathers on the back of her neck are pretty much gone. I never thought to separate them until it was too late. He's only been super aggressive with her while she lays eggs. I've heard of people saying that too many drakes can drown a hen if they all pile on top of her. I could see it happening. A few times, our drake would try to mount the hen while they were in their pond, or....actually EVERY time they were in the water. ( I don't know if being in the water made him more in the "mood" or what... ) She would always try to run, but he was relentless!! Now that she's "not laying", he's backed off. Our drake seems to be quite the aggressor anyway. He will chase us and nip. I think it depends on their personalities too. So I've heard from others, that their drakes are "nice". I have yet to experience this. It seems that our drake may become "dinner", and we'll try again with some new ducklings next year. I don't know how big Indian Runners get, but in comparison with Rouen vs. Pekin, Pekins win by 2/3's! So, take that into consideration too. Overall, ducks are fun..... as long as they have some manners!