Mallards are found across the Northern and Southern Hemispheres; in North America, their range extends from southern and central Alaska to Mexico, the Hawaiian Islands, across the Palearctic, from Iceland and southern Greenland and parts of Morocco (North Africa) in the west, Scandinavia and Britain to the north, and to Siberia, Japan, and South Korea. Also in the east, it ranges to south-eastern and south-western Australia and New Zealand in the Southern hemisphere. Mallards are strongly migratory in the northern parts of their breeding range and winter farther south. They live in a wide range of habitats and climates, from the Arctic tundra to subtropical regions. They can be found in both fresh- and salt-water wetlands, including parks, small ponds, rivers, lakes, and estuaries, as well as shallow inlets and open seas within sight of the coastline. Water depths of less than 0.9 m (3.0 ft) are preferred, with birds avoiding areas more than a few meters deep. They are attracted to bodies of water with aquatic vegetation.
Mallards are diurnal birds that spend most of their time feeding. They usually feed by dabbling for plant food or grazing. They are highly gregarious outside of the breeding season and form large flocks, which are known as "sordes". However, during the breeding season, both male and female mallards can become aggressive, driving off competitors to themselves or their mate by charging at them. Males typically fight more than females and attack each other by repeatedly pecking at their rival's chest, ripping out feathers and even skin on rare occasions. Females may also carry out 'inciting displays', which encourage other ducks in the flock to begin fighting. In general, mallards are noisy birds. Females have the deep ‘quack’ stereotypically associated with ducks. Males make a sound phonetically similar to that of the female, a typical ‘quack’, but it is deeper and quieter compared to that of the female. When incubating a nest, or when offspring are present, females vocalize differently, making a call that sounds like a truncated version of the usual ‘quack’. In addition, females hiss if the nest or offspring are threatened or interfered with. When taking off, the wings of a mallard produce a characteristic faint whistling noise.
Mallards have a monogamous mating system. However, they widely practice so-called “extra-pair copulation”, and paired males are known to chase females that are not their mates. Nesting starts in April, reaching its peak in May. During this period, mated pairs are seen circling in the evenings low over the habitat and looking for a suitable nesting site. When the site is chosen, the female constructs the nest on the ground, near a water body, laying 9-13 eggs, which are incubated for 26-28 days. Chicks of this species are precocial; once born, they are able to swim, being introduced to water within 12 hours after hatching. Right after mating, male mallards usually leave, gathering into male flocks for molting in early June, while the females stay with the offspring, caring for the chicks for 42-60 days. Both males and females reach reproductive maturity at 1 year of age.
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