http://www.centralpets.com/animals/birds/domestic_birds/dbd4863.html


Mallard Ducks spend most of their time foraging for food. They eat a number of items including insects, fish eggs, small fish, tadpoles, wild rice, berries, leaves, green plant shoots, and grain. Most of this food is acquired from foraging in muddy areas in or near the water and embankment of the Mallard Duck's home. The Mallard Duck uses its bill to filter food from the mud.

Now if you are feeding pellets to those YP then look at this :