We recently got 2 welsh harlequins to add to our 2 mallard "flock." The five month old mallards are NOT happy about it. The ducklings are two weeks old. We've had them in a pen where the mallards can see them but not touch them. The two mallards chase them around the outside of the pen and try to bite at them. How long will this keep up? It's been a couple weeks of this. When should I let them actually be together? I assume the mallards are trying to establish dominance but I'm afraid to let them around the ducklings when they are so much smaller. How long should I wait?