Lesser Scaup (Aythya affinis)

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Image of a Lesser scaup
Birds Duck Scaup

Introduction

The Lesser Scaup (Aythya affinis) is a medium-sized diving duck in the family Anatidae. It is widespread across North America and is closely related to the Greater Scaup (Aythya marila). The species breeds mainly in northern wetlands and migrates to inland and coastal waters for the non-breeding season.

Physical Description

Lesser Scaups measure approximately 39–46 centimetres in length, with a wingspan of about 68–78 centimetres. They are compact diving ducks with a relatively short neck and a broad, bluish bill.

Breeding males have a glossy black head, neck and breast, often showing purple or green iridescence in good light. The back is finely marked with black and white vermiculation, while the sides and belly are white. The eyes are yellow, and the bill has a dark nail at the tip.

Females are predominantly brown, with a darker head, a paler face and a variable white patch at the base of the bill. Immature birds and males in non-breeding plumage are more subdued, showing mottled brown and grey plumage. Both sexes show a conspicuous white wing stripe in flight, mainly across the secondaries.

Range and Habitat

The Lesser Scaup breeds across much of Alaska, Canada and the northern United States, particularly in the Prairie Pothole Region, the western boreal forest and adjacent tundra and wetland zones. Breeding habitats include freshwater and brackish wetlands, marshes, ponds and lakes with emergent vegetation. Birds may also nest in nearby grassland or sedge-covered upland areas.

During migration and winter, Lesser Scaups occur on lakes, reservoirs, rivers, estuaries, coastal bays, lagoons and other large wetlands. Many birds winter across the southern United States, Mexico and Central America. They are highly migratory, although some individuals remain year-round in parts of the southern and western range.

Behaviour and Diet

Lesser Scaups are social ducks that commonly form large flocks, especially during migration and winter. They often associate with other diving ducks, including Greater Scaups, Ring-necked Ducks, Redheads and Canvasbacks. They are among the later waterfowl to leave the breeding grounds in autumn and may also return relatively late in spring.

They feed by diving and swimming underwater, generally in water less than about 5 metres deep. Their diet includes aquatic invertebrates such as molluscs, insects, crustaceans and amphipods, together with aquatic plants and seeds. Food use varies with season and location, and birds may feed on small mussels and clams in large lakes and coastal habitats.

Breeding pairs are generally formed seasonally. Courtship displays include head movements, wing and tail flicking, vocalisations and changes in posture. The female usually nests on the ground in grass or sedge, or among emergent vegetation near water. A typical clutch contains about 6–14 eggs, with incubation lasting approximately 26 days. The female performs the incubation, and the precocial ducklings leave the nest within about a day of hatching and follow her to water.

Identification Tips

  • Look for a medium-sized diving duck with a pale bluish bill and a dark nail at the tip.
  • Breeding males have a glossy black head, white sides, a finely barred grey-and-black back and yellow eyes.
  • Females are brown overall and often show a pale or white patch beside the bill.
  • The head of a Lesser Scaup usually has a small peak at the rear, with a relatively flat back of the head and neck.
  • In flight, the white wing stripe is concentrated on the secondaries and does not extend as extensively into the primaries as it does in the Greater Scaup.
  • Greater Scaups are generally larger, with a rounder head, a broader bill and, in males, a more obviously greenish head sheen. Separation can be difficult at a distance, so several features should be considered together.
  • Ring-necked Ducks have a more distinct white ring or band near the base of the bill and a contrasting black bill tip, features that help distinguish them from Lesser Scaups.

Conservation Status

The Lesser Scaup is currently assessed as Least Concern on the IUCN Red List. It remains widespread and common, but long-term monitoring indicates population declines or fluctuations in parts of its range. The North American Breeding Bird Survey recorded a slight decline between 1966 and 2019.

Potential pressures include the loss and degradation of wetlands, reduced food availability along migration routes, contaminants, hunting pressure and broader changes in climate and land use. The species benefits from protection and restoration of boreal and prairie wetlands, conservation of migration and wintering sites, and coordinated waterfowl monitoring and management across North America.

Frequently Asked Questions

Where does the Lesser Scaup live?

The species breeds in Alaska, Canada and the northern United States. Outside the breeding season, it occurs on inland lakes, reservoirs, rivers, estuaries, bays and other wetlands across the southern United States, Mexico and Central America.

How can you identify a male Lesser Scaup?

A breeding male has a glossy black head, a pale bluish bill, a yellow eye, white sides and a finely marked grey-and-black back. The rear of the head often forms a small peak.

What does a Lesser Scaup eat?

Its diet consists mainly of aquatic invertebrates, including molluscs, insects, crustaceans and amphipods, supplemented by aquatic plants and seeds.

Is the Lesser Scaup migratory?

Yes. Most Lesser Scaups migrate between northern breeding wetlands and wintering areas farther south. Migration timing and routes vary according to breeding location and individual movement strategy.

Where does the Lesser Scaup nest?

The female usually places the nest on the ground in grass, sedge or dense vegetation near water. Some nests are located among emergent wetland plants, while others are in nearby upland habitat.

Is the Lesser Scaup endangered?

No. The species is assessed globally as Least Concern, although population monitoring has identified declines or fluctuations and conservation of wetland habitats remains important.

References

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