I saw several ducks during my visits to Fort Worth, TX. This first group, seen at Marine Creek Lake, was caught in the act of mating.

The large black and white duck is a male Muscovy Duck. But this group was acting strangely. If you look closely, you can see that the big balck and white one is holding a smaller one almost underwater. When I watched for a while, the big duck did in fact dunk this little one completely under, and when the small one got away the larger would chase and grab it with its bill. The third duck seemed to be observing. At first I thought they were eating the smaller duck, but after a while the big one let it go, and all 3 swam peacefully to shore. As far as I can tell, this is how ducks mate.