Lesser Scaup
Aythya affinis
小潜鸭
Introduction
Aythya affinis is a diving duck species native to North America. It breeds across inland lakes and arctic marsh ponds from Alaska through western Canada to western Montana, with scattered breeding east of James Bay and the Great Lakes. In winter, it migrates south along the Central and Mississippi Flyways to lakes, rivers, and sheltered coastal habitats from the US-Canada border through Central America to northern Colombia. Notable wintering concentrations occur at Topolobampo lagoons in Mexico and Ciénaga Grande de Santa Marta in Colombia. This species forms a superspecies with the Holarctic greater scaup and is a very close relative. Populations have declined steadily since the mid-1980s, dropping from an estimated 6.9 million birds in the 1970s to approximately 3 million by the late 2000s. Despite this decline, it remains classified as IUCN Species of Least Concern due to its large overall numbers.
Description
This is a small diving duck measuring 38-48 cm (15-19 in) in length and weighing 454-1,089 g (1.001-2.401 lb). Wingspan is 68-78 cm (27-31 in). Adult males in breeding plumage have a black iridescent head with a small hindcrown tuft, black breast, whitish-grey back with darker vermiculations, and white underparts with olive vermiculations on the flanks. The bill is blue-grey with a small black tip. Adult females are dark brown overall with a white band at the bill base and lighter ear region, shading to white on the mid-belly. Males have bright yellow irises; females have orange to yellow irises. Both sexes display white secondary remiges visible in flight.
Identification
The most reliable field mark is white secondary remiges; in greater scaup the white extends onto the primary remiges toward the wingtip. Males in breeding plumage show purple (not green) head sheen and a darker back, but this varies with light conditions. Head shape is crucial when birds are at rest: the lesser scaup has a less bulging forehead and strongly curved or angular nape due to the small crest, whereas greater scaup has a massive forehead and smoother, straighter nape. The bill is smaller, straighter, and narrower than greater scaup. Females and immatures have less white around the bill base, though this varies. Birds in eclipse plumage and females are most difficult to identify, with greater scaup usually appearing bulkier.
Distribution & Habitat
Breeds on inland lakes and arctic marsh ponds from Alaska through western Canada to western Montana, with few breeding east of James Bay and the Great Lakes. Major concentrations occur in Alaska's McKenzie River valley woodlands and Old Crow Flats, where over 500,000 birds gather. Migrates south via Central and Mississippi Flyways in flocks of 25-50 birds, arriving on breeding grounds by May. Winters on freshwater and brackish lakes, rivers, and sheltered coastal lagoons from the US-Canada border through Central America, West Indies, and Bermuda to northern Colombia. Some populations remain year-round in the Rocky Mountains and southern Great Lakes regions. Increasingly observed as vagrants in western Europe, with the first British record in 1987.
Behavior & Ecology
Forages by diving and swimming underwater, sifting through bottom mud, or occasionally dabbling without diving. Diet consists mainly of mollusks (mussels, clams), aquatic plant seeds and parts (sedges, bulrushes, pondweeds, wild celery, wild rice). In winter, also consumes crustaceans, insects and larvae, and small fish. The species has shifted traditional migration routes to exploit zebra mussel populations in Lake Erie. Nests on the ground in shallow depressions lined with vegetation and down, usually among thick vegetation near water. Clutch size averages 9-11 eggs; incubation by female alone lasts about 3 weeks. Young fledge 45-50 days after hatching. Males aggregate during female incubation to molt into eclipse plumage. Becomes sexually mature in first or second summer. Oldest recorded individual exceeded 18 years.
Conservation
IUCN Red List status: Species of Least Concern. Despite having the largest population of any North American diving duck (slightly less than nine-tenths of the continental scaup population), numbers have declined steadily since the mid-1980s. Population estimates dropped from 6.9 million birds in the 1970s to approximately 3 million by the late 2000s. Approximately 57% of nests fail each breeding season due to female mortality or egg predation. Average brood size is 8.33 hatchlings. Causes of decline remain unknown but may include pollution, habitat destruction in wintering regions, reduced breeding success, and potential competition with increasing greater scaup populations. Hunting is not currently considered a major impact factor.
Culture
The species is colloquially known as 'little bluebill' or 'broadbill' due to its distinctive blue bill. The name 'scaup' may derive from the Scottish word 'scalp' referring to clams, oysters, and mussels that the bird feeds on, though some sources attribute it to the female's discordant 'scaup' call.
Source: Wikipedia · CC BY-SA 3.0
Taxonomy
- Order
- Anseriformes
- Family
- Anatidae
- Genus
- Aythya
- eBird Code
- lessca
Distribution
breeds North America from northern Alaska and western Canada southward through northern California, southern Colorado, and Minnesota (USA); winters to Hawaiian Islands, the Caribbean, and northern South America
Data Sources
Species description from Wikipedia, licensed under CC BY-SA 3.0.
Taxonomy data from AviList 2025.