Greaters have more rounded heads and a longer wing stripe. They are more coastal in winter, favoring less sheltered and saltier water. They are generally scarce inland except on their northern Canadian breeding grounds, but occasionally can be found in flocks of lesser scaup.
Greaters feed throughout the day, diving for mollusks and grass seeds, but plants make up only a small part of the diet in winter. Silent most of the year, the calls are nearly identical to those of lesser scaup. Recent studies suggest that the population may have declined significantly in recent decades, but the cause is not known.