There are a 100+ mallards wintering on the ponds at the Eldorado Golf course in McKinney, and they have been fun to watch.
On a couple of occasions they seem to be chasing insects, at least their heads down and quick changes in direction (for a duck on land) seem to indicate that.
It is also a good time of year to start watching for mating behavior. Mallards pair up in the winter, with the male following the female back to her home each spring. I have seen males fighting and exhibiting courtship displays.
If you are watching mallards and hear the loud quack, quack, quack call, it is a female. The males have a much lower, less emphatic call.