I'm curious about this myself but have a slightly different issue. We had 6 ducks. 4 hens, 2 drakes. Introduced 2 more hens and 1 more drake that are alightly older (7 months old to the original's 4 months). My original hens are going after the new drake (even really ganging up when all 4 attack at once). I'm also keeping them separated by closing new ones into the house(shed) at night (originals free range during daylight) and leaving originals in duck run. Then in morning I let originals out to free range and new ones get the whole pen. They seemed good yesterday. Originals all snugged up to the pen right next to the new ones. Everyone sleeping. So I thought "hey I'll let them be together outside and see how it goes". Watched them for an hour (didn't interfere. Just sat there to make sure no one really got hurt). They picked on the drake the whole time and chased him all over the yard, until I put newbies back in. No one hens, drakes or even goose notice the new girls. It's just the original hens ganging up on the new drake. Help!