They practice doing the deed. Ours seems to switch out who is on bottom and who is on top although the more dominant one is usually on top more and most often. It is just something they do. I have no idea as to adding a male, we have no males.I have another question. I have two females, which I am sure of because I separated them within their house and both of them lay eggs. But now the bigger, louder female is holding the smaller one under the water on top of her and biting her neck. Is this a dominance issue like dogs? you think if I got a Drake that this behavior would stop? its not that often and it doesn't last that long so I'm not too worried, just makes me curious