Most mallards in North America spend the winter across the central and southern United States, roughly between the Canadian border and the Gulf Coast. USGS tracking data from 2018 to 2020 mapped wintering birds across a range stretching from about 30°N latitude (southern Texas and Louisiana) up to 49°N (the U.S.–Canada border), and from the Great Plains eastward to the western Appalachians. How far south any individual bird travels depends heavily on how cold it gets and how quickly.
What Triggers the Move South
Mallards don’t migrate on a fixed calendar. Cold snaps push them. Minimum daily temperature is the single strongest predictor of when a mallard leaves its breeding grounds, and the probability of departure stays low until temperatures drop below about minus 5°C (23°F). Below that threshold, each additional 1°C drop increases the chance of departure by roughly 29 percent. The colder the day, the farther the birds fly in a single push: on average, about 166 kilometers farther for each 1°C decrease in temperature.
Shrinking daylight plays a supporting role. Between the autumn equinox and the winter solstice, each one-hour decrease in day length roughly doubles the likelihood that a mallard will take off. Tailwinds seal the deal. Birds are significantly more likely to migrate on days when winds blow in the direction they’re already headed, letting them cover ground with less energy.
This means migration timing varies widely by year and location. In a mild autumn, mallards may linger on northern lakes well into November or even December. A sudden Arctic blast can send thousands south overnight.
Where They Settle for Winter
In North America, the primary wintering corridor runs from Nebraska and Missouri south through Arkansas, Mississippi, Louisiana, and into the Texas Gulf Coast. Large numbers also winter along the lower Mississippi River valley and in the rice-growing regions of the southern Plains. Some mallards stay surprisingly far north if they can find open water, particularly near power plants, spring-fed streams, or urban areas where water rarely freezes.
European mallards follow a different axis. Birds breeding in Scandinavia and northwestern Russia migrate southwest through Sweden, then continue toward northern Germany, Denmark, and the Netherlands. Those in central Europe shift along a general southwest-to-northeast corridor, wintering in milder Atlantic-influenced climates. Wherever the population, the pattern is the same: mallards move just far enough to find unfrozen water and food, and no farther.
Choosing a Winter Home
Wintering mallards are picky about their roosting spots. Studies of radio-tagged birds in Nebraska found that they roosted on rivers and irrigation drainage canals almost equally, splitting about 47 and 46 percent of their time between the two. The river roosts they preferred were ice-free flood pools and beaver ponds near wooded banks and treeless sandbars. On canals, they favored east-west channels with tall north banks and trees that blocked northwest winds and kept snow from drifting into the water.
During the day, the birds leave these roosts to feed. Corn stubble fields are the main attraction. After heavy snowstorms, cattle feedlots draw large flocks looking for exposed grain. Mallards also use mowed alfalfa fields, grazed pastures, and shallow marshes for dabbling and loafing when conditions allow. The common thread across all these sites is protection from wind, access to open water for nighttime roosting, and nearby agricultural fields for daytime feeding.
What They Eat to Survive the Cold
A mallard’s winter diet looks nothing like its summer menu. During breeding season, females eat mostly aquatic invertebrates to get the protein and calcium they need for egg production. In winter, the priority flips to raw calories. Birds switch to a carbohydrate-heavy diet of natural seeds, waste agricultural grain (especially rice and corn), and underground roots and tubers.
Agricultural grain is energy-dense but nutritionally incomplete. It lacks certain amino acids and minerals, so mallards still need to supplement with natural seeds and whatever invertebrates they can find in unfrozen wetlands. This nutritional balancing act is one reason mallards seek out diverse habitats rather than parking on a single cornfield all winter. The availability of waste grain on harvested cropland has actually allowed some mallard populations to expand their winter range northward, staying closer to breeding grounds because they can find enough food to fuel their metabolism in the cold.
Building Fat Reserves
Surviving winter requires serious energy storage. Female mallards arriving at wintering areas in early fall are typically lean, weighing around 1,010 grams with only about 65 grams of body fat. Over the following weeks, they gain substantially. By the time they complete their fall feather molt and begin pairing up in November and December, they’ve added roughly 127 grams of body mass and more than doubled their fat stores to around 134 grams.
Fat reserves matter for more than just staying warm. Paired females consistently carry more fat than unpaired females throughout the winter, and birds with fewer than 125 grams of lipid reserves are rarely paired at all. Fat stores essentially signal a bird’s fitness and readiness to breed. By late winter, females preparing to migrate north are at their heaviest, around 1,280 grams with 219 grams of fat. That stored energy fuels both the spring migration and the early stages of egg production before they even reach their breeding grounds.
How They Handle Freezing Temperatures
You’ve probably seen mallards standing on ice or paddling in near-freezing water and wondered how their bare feet don’t freeze. The answer is a heat-exchange system built into their legs. Warm arterial blood flowing down toward the feet passes right alongside cold venous blood returning to the body. Heat transfers from the warm blood to the cold blood before it ever reaches the feet, so the legs and feet stay just above freezing while the bird’s core stays warm. This countercurrent system is remarkably efficient. Research published in Biology Letters confirmed that birds control heat loss through their legs far more effectively than through other exposed body parts like their bills.
This adaptation is a big part of why some mallards can overwinter in places where temperatures regularly dip well below zero. As long as they can find a patch of open water and enough food to maintain their fat reserves, their physiology handles the rest.
Not Every Mallard Migrates
Mallards are partial migrants, meaning some individuals in a population migrate while others stay put. In mild winters, a substantial number of birds remain on northern lakes, rivers, and urban ponds year-round. City parks with open ponds and regular food sources (including bread from well-meaning visitors, though natural food is healthier) can support resident flocks through the entire winter. The decision to migrate or stay appears to depend on local conditions, individual body condition, and possibly learned behavior from previous years. Older birds show stronger attachment to familiar flyways and wintering sites, returning to the same areas season after season.