Greater scaup is fairly shallow and has an abundance of food sources and cover. The female lays six to nine olive-buff-colored eggs, which she incubates for 24–28 days. A larger clutch could indicate brood parasitism by other greater scaups or even ducks of other species. Newly hatched chicks are covered with down and are soon able to walk, swim, and feed themselves; however, they are not able to fly until 40–45 days after hatching. The vulnerable small chicks follow their mother, who protects them from predators. The greater scaup dive to obtain food, which they eat on the surface. They mainly eat
New Zealand scaup for twenty to thirty seconds and go down three metres to look for aquatic plants, small fish, water snails, mussels and insects. It is sometimes seen with the Australian coot ("Fulica atra"); it is thought that the scaup takes advantage of the food stirred up by the coots as they fossick for shrimps. It is found throughout both the North and South Islands of New Zealand in deep freshwater lakes and ponds. Unlike other members of this genus, the scaup is not migratory, although it does move to open water from high country lakes if they become frozen in winter.