What breed of duck do you have? It sounds like you have Muscovy, which that is pretty typical behavior for establishing a pecking order. If you have Muscovy, I would leave them together unless you see blood. It actually sounds pretty tame for Muscovy.Development in the situation. I have watched the action happen in full, finally. Caught her laying down on the ground, in front of them, and he started pecking at her neck and ripping feathers off her wings. Then she got up and ran towards me, chirping erratically. I have separated him again.