Interestingly I hatched a pair of Rouen St Clair, which do not really mature until 18mth old. Knowing drakes need more females I got in two younger Rouen ducks. All 4 lived together happily until next breeding season, when the drake kept attacking the younger ducks. I thought at first he was just trying to mate them, but no - he and the duck kept them both off the pool and away from the feed to such an extent I had to separate them. Breeding season over, calm returned!!
I think we often forget that animals/birds have personalities of their own, and also I think we forget that we ourselves are just one species of mammal. We put ourselves so far above anything else, and sometimes I wonder why?
All the best
Sue