Greater scaup

Aythya marila

Grote topper / Bergente / Fuligule milouinan

The greater scaup, just scaup in Europe, is a mid-sized diving duck though it is larger than the closely related lesser scaup. It is a circumpolar species, which means that its range circles one of Earth's poles. It spends the summer months breeding in Alaska, northern Canada, Siberia, and the northernmost reaches of Europe. During the winter, it migrates south down the coasts of North America, Europe, and Japan.

Greater scaup nest near water, typically on islands in northern lakes or on floating mats of vegetation. They begin breeding at age two, but start building nests in the first year. The drakes have a complex courtship procedure, which takes place on the return migration to the summer breeding grounds and concludes with the formation of monogamous pairs. Females lay a clutch of six to nine olive-buff colored eggs. The eggs hatch in 24 to 28 days. The down-covered ducklings are able to follow their mother in her search for food immediately after hatching.

Greater scaup eat aquatic mollusks, plants, and insects, which they obtain by diving underwater. They form large groups, called "rafts", that can number in the thousands. Their main threat is human development, although they are preyed upon by owls, skunks, raccoons, foxes, coyotes, and humans. 

This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Although the population may be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern (IUCN, 2012).

Greater scaup are rated as a species of least concern by the IUCN Redlist. During aerial population surveys greater and lesser scaup are counted together, because they look almost identical from the air. It was estimated that the greater scaup made up about 11% of the continental scaup population. Since the 1980s, scaup populations have been steadily decreasing. Some of the primary factors contributing to this decline are habitat loss, contaminants, changes in breeding habitat, and a lower female survival rate. The 2010 American scaup population survey was 4.2 million scaup, however, the worldwide greater scaup population survey estimated 1,200,000 to 1,400,000 mature greater scaup. Along with the aerial population surveys, there is a banding program for the greater scaup. Metal leg bands are placed on them, so that if the scaup is killed by a hunter or if it is captured by another banding group, the number on the band can be reported to biologists and wildlife organizations. These banding programs yield valuable data about migration patterns, harvest rates, and survival rates.

Summer breeding grounds of the Greater Scaup range across the northern limits of Europe (including Iceland) and Asia, through the Aleutian Islands (year-round breeding) to Alaska (USA), and across to the Atlantic coast of Canada (del Hoyo et al. 1992). It winters further south, reaching California, the great lakes and northern Florida in North America, the Adriatic Sea and northern Black Sea in Europe, the western Caspian Sea, and on the Pacific coast of Asia as far as south-east China (del Hoyo et al. 1992).

The global population is estimated to number c.1,200,000-1,400,000 individuals (Wetlands International 2006), while national population sizes have been estimated at c.50-1,000 individuals on migration and c.50-1,000 wintering individuals in Taiwan and c.1,000 wintering individuals in Korea (Brazil 2009).

The species is susceptible to oil pollution (Kirby et al. 1993, Kear 2005b) when moulting and in winter and may be threatened by high levels of organochloride contaminants (Kear 2005b). Its habit of congregating around coastal sewage outlets in the winter also puts it at risk from other pollution types (del Hoyo et al. 1992) and large numbers often drown due to entanglement in fishing nets (Kirby et al. 1993). The species is threatened by hunting for sport in North America (Schmidt 2006, Blohm et al. 2006), and suffers from disturbance from hunting (Evans and Day 2002). It is also susceptible to avian influenza, so may be threatened by future outbreaks of the virus (Melville and Shortridge 2006). The species is hunted legally for sport in seven countries of the European Union (Kear 2005b) (e.g. Denmark [Bregnballe et al. 2006]), and is hunted for commercial and recreational purposes in Iran (Balmaki and Barati 2006).

Above: Greater scaup, adult drake

Above: Greater scaup, adult female

Above: Greater scaup, adult drake

Above: Greater scaup, adult female

Above: Greater scaup, adult female

Above: Greater scaup, adult pair (drake in front).

Above: adult male Greater scaup

Scaups and closest related diving ducks (genus Aythya): (1) greater scaup, (2) lesser scaup, (3) ring-necked duck, (4) tufted duck and (5) New-Zealand scaup. Click image to enlarge.