I've got 10 ducks: 5 Rouens, 2 Pekins, 1 Swedish Blue, and 2 Cayugas. We were hoping for a Drake and a Hen, or 2 Hens. But, as both of them are fairly quiet quackers, I had thought that they were both drakes (although it's hard to tell with my Pekin hen making all that noise!). But, I keep looking at them and they are clearly different sizes. That seems like it might be sexual dimorphism like the Pekins. They are about 13 weeks old now. My Rouen drakes just got their adult plumage in, so I'm thinking it may be another month before the Cayugas do the same. But just based on the size I can't tell if I have a boy and a girl, or if one boy is larger than the others. In this first photo they are about 8 weeks old. Based on size, I think the one on the left is a drake and the other is a hen. And in this photo they are about 12 weeks old. But they both appear to have the same coloring and a quiet quack, so I'm not sure. (That's our Swedish Blue, Momma Duck, with them). But there's still a noticeable size difference between them.