Courtesy Kenn Kaufman
From Alaska's Seward Peninsula, the Greater Scaup breeds at scattered sites southeast across northern Canada. Significant numbers also breed along the east coast of Hudson Bay and on Canada's Ungava Peninsula. Greater Scaup winter along the Pacific coast from Alaska to Baja California, and along the Atlantic coast from Newfoundland to Florida, with most ducks ranging from Cape Cod to New Jersey. A significant population uses the Great Lakes until they freeze.
In Europe and Asia, the Greater Scaup breeds from Iceland through northern Russia and winters from the British Isles south and east through the inland seas and then along Asia's Pacific Coast.
A legend for the range map to the right can be found here
The Greater Scaup frequents calm or slow-moving water, and is found on salt water more often than the Lesser Scaup. This scaup breeds on the large lakes and bays of the Arctic flatlands, especially the tundra. Smooth shorelines are generally avoided. Basic requirements include shallow water, aquatic vegetation for hiding ducklings and for foraging, and wind protection for ground nests. In winter, Greater Scaup prefer shallow saltwater such as bays, lagoons, large tidal pools, and slow moving estuaries. Some large freshwater lakes are also used where food is abundant.
The Greater Scaup's heavy body and fully webbed feet help it dive as deep as 20 feet for up to 60 seconds. In winter, feeding flocks can be very large. This scaup is omnivorous and shifts its diet to whatever foods are most abundant, including insects and their larva, seeds, the succulent parts of aquatic plants such as muskgrass, wild celery, and sea lettuce, small mussels, clams, snails, crustaceans, marine worms, and fish eggs. Over the last ten years, the invasive zebra mussel in the Great Lakes has become an important but potentially dangerous food source, since these filter feeders concentrate pollutants.
Before and during migration, Greater Scaup form monogamous pairs which appear to last only one season. Several males court a female with displays, terrestrial and aquatic chases, and vocalizations that include coughs and whistles. Males without a mate often challenge mated pairs. In thick vegetation near water, the female makes a scrape and fills it with grasses, in which 6 to 8 olive-brown eggs are then laid and covered with down. The male departs about halfway through the 23 to 28 days required for incubation. Females defend nests and young with distraction displays to ward off ravens, arctic foxes, and various gull species.
Within a day of hatching, the female Greater Scaup leads the downy chicks to water, where they begin to feed in the shallows near cover. The female departs for staging areas before the young can fly. When they are between 35 and 42 days old, the juvenile Greater Scaup join other young and adults to prepare for the fall migration.
Cold weather in fall and lengthening days in spring both stimulate migration. Small flocks of Greater Scaup sometimes travel together in large formations along traditional routes. Starting in early September and continuing through December, males migrate first, followed by juveniles mixed with females. In early March, mature Greater Scaup of both sexes migrate north, followed by the young, to arrive on the breeding grounds in May.