Although the bird can dive in an emergency, it rarely does so. The food of the Mallard depends on seasonal requirements for egg-laying, moulting, or putting on body fat for migration and winter. Most food material is vegetation or invertebrates procured in the water or on the land. The bird feeds on emergent weeds, roots of plants that grow in shallows, and small swimming invertebrate animals or larval stages of insects that occur in a muddy bottom. On land it often turns to grain, and large flights of Mallards can be seen feeding in harvested grain fields in fall.
Mallards are hardy ducks, wintering regularly in southern Ontario and southern British Columbia.
Some will remain as far north as they can find open water. Even in Alaska, some birds are found throughout the colder months, and in Alberta, Mallards stay on the open waters of the North Saskatchewan River as far north as Edmonton. Mallards are one of the first ducks to arrive back on the breeding grounds in spring. They are adaptable and may nest near a lake, pond, river, or even woodland pool. Their preferred habitats, however, are the natural grasslands that surround little reed-ringed sloughs and potholes on the prairies.