We have two call ducks... A mallard and an unknown breed. The mallard's a male and the unknown is female. They're about the same age... around 7-+ months. Why is she so small?? She's about half the size he is... Is it just the breed/age/gender? We used to have two crested ducks (lost to predators)..one male and one female.. they were the same size... and both were about twice as big as the mallard..