I have 6 Pekin ducks and there are 4 males and 2 females. I know this may not be the best ratio and I am waiting to see if they start fighting. But when they go in their little pond, sometimes one will get on the back of a female and keep it under until the one goes for air. I'm not sure if this is them mating, or if they are being malicious. They don't really be agresssive to eachother otherwise though.