According to a friend of mine who is taking Animal Behavior at University of
Madison, the Animal Behavior field is full of papers on courtship behavior
of mallards -- largely because it's pretty easy to see (lots of mallards,
and they don't exactly hide in bushes, they feel safe in the middle of large
ponds, which are within visual range.)

I seem to recall him saying that not only do Mallards have courtship
behavior but they have some downright unsavory (from the human perspective)
courtship behaviors (e.g. apparent 'rape') as well.

Check the Animal Behavior magazine citations, I guess,

Leslie Schweitzer