Twice now I have caught two of my 12 week old male white Chinese ganders ganging up on my Cayuga duck. One gander holds her head under water and the other attempts to mate her. I can hear the poor thing trying to quack and it sounds more like a glub-glub. I have been able to separate them but what if I'm not around? These are free-range birds that were raised together. Is there any way to protect my duck other than whacking the ganders? And why is it always the Cayuga?