Adult males lose their bright breeding plumage by the end of July and take on an eclipse plumage similar to that of the females. In fall and early winter male mallards again assume the same colorful plumage that they have in the spring. The mallard is one of the earliest ducks to migrate into North Dakota in the spring. Usually many have arrived by the end of March, and peak numbers are present in the state in April. In the fall, locally raised mallards may congregate on the larger waterfowl marshes during late September and early October and often are present in the state until the time of the general freeze-up in November.
Mallards often spend the winter as far north as open water and food supplies allow.
In most winters, small flocks may be found along the Missouri River and other places in North Dakota. Major wintering areas, however, include reservoirs, flooded hardwood river bottoms and streams in the southern United States and Mexico. The mallard is a surface feeder and is commonly observed tipping up to feed in shallow water. It also feeds on dry land, such as stubble fields where corn, wheat, barley, and other foods are available. In spring, the diet of the female is high in animal matter such as insects and other invertebrates, which are needed to sustain her during egg laying.