Lesser Scaup (Aythya affinis)
by Wanda Gorsuch

Common Names: bluebill, little bluebill, broadbill

In North America, the total population of lesser and greater scaup has been decreasing by an average of 150,000 birds a year.  Scientists are working on figuring out the many factors that may be contributing to this decline.  Since lesser scaup make up about 89% of the total population, they are of particular research interest.

Identification

It can be challenging to distinguish lesser scaup from greater scaup in the field.  Greater scaup have a more rounded head, while the head of the lesser scaup is smaller and squarer.  The other important distinguishing factor is the nail at the tip of the bill.  Lesser scaup have a narrower nail while greater scaup have a wider nail, with more black and a deeper bill.

Males sport a glossy black purple head with a slate blue bill.  Neck, breast, upper mantle and undertail region are black.  Belly and flanks are white and the lower mantle is flecked with gray.

Hens are a bit more subdued in an overall color range from grayish brown to chocolate brown.  They have a white patch at the base of their gray bill.  Upper body is darker and wing coverts are flecked with gray.

Both sexes have a partial white stripe across the back edge of the upper wing.

Distribution

In breeding season, lesser scaup are found throughout the interior of Alaska and Canada and in some areas of the western US to California, Nevada, Colorado, South Dakota and Minnesota.  In the winter, most lesser scaup are found on the Louisiana coast, Florida coast, and Gulf Coast of Mexico.  Large numbers also winter along the Pacific Coast.  Other wintering locations include the Caribbean and Central America to northern South America.  Small groups can be found throughout central US and interior of Mexico.

Habitat

Lesser scaup use fresh to moderately salty seasonal and semi-permanent wetlands and lakes with emergent vegetation during the breeding season.  In the winter months, lesser scaup favor coasts of lakes, reservoirs, and fresh to brackish coastal bays and estuaries.  Unlike other diving ducks their winter distribution does not seem to be closely related to aquatic plant foods.

Food

The diet of the lesser scaup is mainly made up of aquatic invertebrates like insects, crustaceans and mollusks.  In some areas, seeds and aquatic plants are important.

Reproduction

Lesser scaup are one of the latest of North American ducks to form pair bonds.  Generally bonding occurs late in spring migration. 

Lesser scaup like to nest on or near water in tall vegetation.  Occasionally they will nest upland, far from water.  The actual nest is constructed with grasses or other vegetation around the nest site throughout the laying and incubation period.  The first egg is laid when the nest bowl is only a scrape in the ground.

Hens lay about 8-10 eggs in total.  One egg a day is laid early in the morning.  Incubation starts slowly during laying and begins full time within 24 hours after the last egg is laid.  Incubation lasts for around 21 – 27 days.  Only hens incubate the eggs.

Eggs normally hatch within 24 hours of each other.  Hens lead ducklings from the nest within 24 hours of hatching, once their down is dry.  Ducklings are able to feed themselves.  On their first day they can dive, but are too buoyant to stay under.  By 5-7 weeks of age they can diver for 2 – 25 s and swim underwater for 15-18m.

Conservation and Management

Lesser scaup are the most abundant diving duck in North America.  However, scaup populations have been steadily declining on a continental scale and are well below the population goal set by the North American Waterfowl Management Plan (NAWMP).  Several theories have been put forward such as the effect of contaminants and lack of nutrient reserves (body fat) for the decline.  Scientists are still working on putting this puzzle together.

Sources of Information

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.). Philadelphia: The Academy of Natural Sciences; Washington, D.C.: The American Ornithologists’ Union.

Bellrose, F.C.  1976.  Ducks, geese and swans of North America, 2^nd edition. Stackpole Books, Pennsylvania.

Johnsgard, P.A.  1978.  Ducks, geese, and swans of the world. University of Nebraska Press, Nebraska.