Flies quickly with fast-beating wings and an audible whirr.
Swims quickly and low in the water, diving frequently with smooth action. May travel for 30-40 metres before surfacing, staying submerged for up to a minute. When disturbed it flies up quickly, gaining height rapidly. Hardheads feed only in water, and are able to dive to deep food sources unavailable to other ducks. They can eat at the surface, taking seeds from surface aquatic plants but also submerge to reach insects, molluscs, shrimps, yabbies and small fish as well as sedges, grasses and submerged plants.
Common in south east and south west Australia. Nomadic in normal seasons, following the rains. Gathers into rafts of arriving and departing birds numbering in the thousands floating in open water. During drought they wander more widely throughout Australia, inland and in the north, and reach Indonesia, New Guinea and New Zealand.
Breeding in the spring depends on rainfall and takes place in October and November in the south-west and September to December in inland New South Wales but can breed later if flooding is extensive. Nest is a cup of neatly woven reeds and sticks built in dense reeds or other vegetation in water about 1 metre deep. Usually 9 to 12 eggs, glossy cream, oval 57mm by 41mm. The female incubates the eggs for about 25 days.
Hardheads have declined in numbers on the east coast but are still common inland.