Lesser Scaup

Aythya affinis

(c) Glen Tepke
  • Swans, Geese, Ducks
  • Anseriformes
  • Pato boludo-menor, Pato del medio
  • Petit Fuligule, Petit morillon
Appearing like flecks of black, white, and brown floating low in the water, a raft of Lesser Scaup can look like a rough patch on a wind blown lake. Common from Alaska to Nicaragua, this diving duck has many names, including blackhead, bullhead, blackjack, and river bluebill. Although closely related to the Greater Scaup, with which it was considered one species before 1838, the Lesser Scaup usually flocks by itself and prefers fresh over saltwater.
(c) Glen Tepke
Appearance Description
On average, this marine duck is 16.5 inches long, weighing 1.8 pounds, with a wingspan of 25 inches. A medium-sized diving duck, the Lesser Scaup has several plumages depending on age, sex, and time of year. From October to June, the drake presents a classic black and white contrast. A black head, chest, and rear parts frame white sides and a grayish back that becomes darker toward the tail. This gray is produced by fine, wavy bars of black and white rather than gray feathers. All adults have golden eyes and a blue bill, tipped with black. During the breeding season, dark brown colors the female’s chest and head. A clean, bold white patch marks the female’s face at the base of the bill. Her body is gray-brown above, with a darker tail. Both sexes flash a white patch in the upper wing and whitish under-wings.
The Lesser Scaup is difficult to distinguish from the Greater Scaup. The Lesser Scaup has a more angled crown when relaxed, a darker grey back and barring in the sides of the breeding male, a shorter wing stripe in flight, and a slighter build.
Range Map
Courtsey Kenn Kaufman
Range Distribution
The Lesser Scaup’s breeding range stretches from Alaska to Ontario and dips southward through the Great Plains to northern New Mexico. Nearly 66% of all Lesser Scaup breed in Canada’s boreal forest region. This diving duck winters across a broad range from Washington south into Nicaragua, and from Central California east through Texas. The winter range also covers almost the entire eastern United States south of a line roughly from Texas through the Great Lakes to southern New England.  
A legend for the range map to the right can be found here.
While some Lesser Scaup winter coastally, open, shallow freshwater is used most often. Lesser Scaup breed on the shallow lakes and ponds of the boreal forest and seasonal pools of prairie potholes, where spring vegetation is emerging and underwater vegetation is abundant. The only North American diving duck to breed at significant elevation, this scaup also breeds in the Rocky Mountains. During migration and winter, large lakes, ponds, rivers, reservoirs, near shore coastlines, saltwater bays, and estuaries are important sites for this duck.
The Lesser Scaup is well adapted for aquatic foraging; its feet are set so close to its tail that diving is efficient, although walking is a little clumsy. Usually in freshwater water 5 feet, but occasionally up to 20 feet deep, the bird dives at an angle and resurfaces far from the initial dive. The seeds of aquatic plants such as yellow pond lilies and bullrushes, and the soft parts of waterweed and pondweed are important foods year round. Animal prey includes leeches, snails, amphipods, fingernail clams, surf clams, zebra mussels, shrimp, herring eggs, small fish, and surface insects like midges. The scaup’s diet varies with the season and food abundance.
During spring migration, Lesser Scaup form monogamous pairs. Courtship displays include a quick head toss accompanied by a quiet “wheee-ooo.” Females respond with an extended neck, raised bill, and a growl call. While Lesser Scaup drakes do not defend territories, they do attack other males during egg laying. Located in thick, new vegetation, usually near water, the nest is a simple depression lined with grasses and finished with down. The female incubates 8 to 10 olive eggs for 21 to 27 days, during which time the male departs. Where breeding densities are high, Lesser Scaup may lay eggs in other ducks’ nests; in turn, they sometimes host Redhead, Gadwall, and Ruddy Duck eggs.

The downy chicks can walk, swim, and dive within a day of hatching. After the female Lesser Scaup leads them to water, chicks feed independently on surface insects for about two weeks until they are heavy enough to remain underwater. Lesser Scaup hatchlings from different clutches sometimes form crèches, which one or more adult females may defend. Lesser Scaup can fly between 47 and 61 days of age.

In shapeless groups or V-formations, Lesser Scaup migrate at night and respond to weather patterns like hard freezes and approaching fronts. Migration patterns shift with food availability, so that flyways are not closely followed. Fall migrants often depart in large groups that can number in the thousands. Fall migration can be delayed by molting; most Lesser Scaup migrate in late October to mid-November, making them one of the latest arrivals on the wintering grounds. Spring migration begins as early as late February and extends well into May.  
CBC Graph
Graph Legend
Annual Population Indices
  • 4,400,000
  • 4,400,000
Population Status Trends
The Lesser Scaup is among the most abundant ducks in North America, but it has been declining significantly over the last 30 years. In 2006, combined winter estimates of Lesser and Greater Scaup set a record low—37% under the long-term average. Between 1966 and 2003, Breeding Bird Surveys recorded significant population declines, especially in the southern and central ranges. Statistical analyses reveal that the Lesser Scaup’s population is becoming older, and has fewer females. The U. S. Fish and Wildlife Service lists the Lesser Scaup as a “game bird below desired condition” and a “conservation management concern.” Alabama, Idaho, and Wyoming consider it a “species of conservation concern.”
An explanation of the Annual Indices graph displayed to the right can be found here.
Conservation Issues
Invasive plants, landfills, wetland drainage, and water level control have fundamentally altered the Lesser Scaup’s migrating and wintering habitat. Siltation and the westward spread of fish, which the scaup do not eat, have reduced the prey on which Lesser Scaup depend. Zebra mussels in the lower Great Lakes provide an alternative food source, but this invasive mussel competes with native prey, and concentrates pollutants, which the scaup ingest. Increased lumber and petroleum extraction also impact the boreal forest, where this scaup breeds.
In coordination with the North American Waterfowl Management Plan, conservation groups like Ducks Unlimited seek to investigate population declines and preserve more open-water wetlands. The Important Bird Areas project has targeted key migrating sites for the Lesser Scaup, like eastern Lake St. Clare and the lower Detroit River, both in Michigan.
What You Can Do
The logging of boreal forests is driven by consumer demand for paper. Buy paper products high in post-consumer recycled content and reduce the number of catalogues and magazines you receive. Visit the Boreal Songbird Initiative to learn more.
Become familiar with the issues surrounding mercury emissions that poison waterfowl like the Lesser Scaup and share your concerns with your state and federal representatives.
Consider purchasing a Federal Duck Stamp to help provide for the protection of and research on Lesser Scaup.
For more actions you can take, including Audubon activities, please visit our resources page.
More Information
Learn more about the Lesser Scaup through Ducks Unlimited .
Visit our resources page for more information about this species.
Natural History References
Austin, J. E., C. M. Custer, and A. D. Afton. 1998. Lesser Scaup (Aythya affinis). In The Birds of North America, No. 338 (A. Poole and F. Gill, Eds.). The Birds of North America, Inc., Philadelphia, PA.
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996.
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, New York. 2000.
Conservation Status References
Austin, J. E., et al. 2000. “Declining scaup populations: issues, hypotheses, and research needs.” Wildlife Society Bulletin 28:1 (2000) 254-263.
Austin, J. E., C. M. Custer, and A. D. Afton. 1998. Lesser Scaup (Aythya affinis). In The Birds of North America, No. 338 (A. Poole and F. Gill, Eds.). The Birds of North America, Inc., Philadelphia, PA.
Badzinski S. and S. Petrie. “Diets of Lesser and Greater Scaup During Autumn and Spring on the Lower Great Lakes.” Wildlife Society Bulletin 34:3 (October 2006) 664–674.
Chipley, Robert M., George H. Fenwick, Michael J. Parr, and David N. Pashley. The American Bird Conservancy Guide to the 500 Most Important Bird Areas in the United States. New York: Random House, Inc. 2003.
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, New York. 2000.