Aythya affinislesser scaup

Geographic Range

Lesser scaup are an American species of diving duck. They breed in interior boreal forests and parklands of Alaska and Canada and into the United States in North and South Dakota, Montana, Wyoming, northeastern Washington, and the Klamath region of southern Oregon and northeastern California. In winter they are found in appropriate habitat in the Pacific coastal states, the southern states, including Colorado, the southeast, Florida, and along the Atlantic coast to Massachusetts. They are also found in the southern Great Lakes region and Ohio and Mississippi river drainages. Lesser scaup also winter throughout Mexico and Central America, the Antilles, and the Hawaiian Islands. Occasional birds are seen in winter in the western Palearctic, Greenland, British Isles, Canary Islands, and the Netherlands. (Austin, et al., 1998)


Lesser scaup are reliant on wetland habitats for foraging and breeding. They are found throughout the year on semi-permanent or seasonal wetlands with emergent vegetation (such as cattails, Typhus, or bulrushes, Scirpus) or submergent vegetation (pondweed, Potamogeton, water milfoil, Myriophyllum spicatum, hornwort, Ceratophyllum demersum, or muskgrass, Chara). They are most abundant in ponds with high amphipod abundance and intact wetland margins. They are found in freshwater or slightly brackish wetland areas, including ponds, lakes, river impoundments, and coastal bays. Preferred wetlands are fairly shallow. Lesser scaup nest in wetland meadow or grassland areas near ponds. (Austin, et al., 1998; Lindeman and Clark, 1999)

Physical Description

Lesser scaup are medium-sized diving ducks. Males are slightly larger than females: from 40.4 to 45.1 cm in males and 39.1 to 43.4 cm in females, and from 700 to 1200 g in males and 600 to 1100 g in females. Males and females have different plumage patterns throughout most of the year. Males in breeding plumage (August to the following June) have a blue bill, purplish-black head, breast, neck, tail, and vent. The sides and belly are white and the back is white with grey flecking. Females are chocolate brown, with lighter sides, a rufous head, and a white patch at the base of their dark grey bill. In all birds the secondary feathers are white at the end, resulting in a white wing stripe on the trailing edge of the upper wing surface. Iris color varies with sex and age. Irises are grayish in hatchlings, become yellow-green in juvenile males, and then deep yellow in adult males. Iris color in females stays a brownish color. (Austin, et al., 1998)

Lesser scaup are difficult to distinguish from their close relatives, greater scaup (Aythya marila), especially at a distance. There is no documented geographic variation and no subspecies described. (Austin, et al., 1998)

  • Sexual Dimorphism
  • male larger
  • sexes colored or patterned differently
  • male more colorful
  • Range mass
    600 to 1200 g
    21.15 to 42.29 oz
  • Range length
    39.1 to 45.1 cm
    15.39 to 17.76 in


Lesser scaup are monogamous. Mate-switching is common during the breeding season. Pairs are formed during late spring migration and last only until the females have been incubating the eggs for some time. Forced extra-pair copulations are common. (Austin, et al., 1998)

Lesser scaup are one of the latest nesting ducks in North America. Most individuals arrive on breeding grounds by May and nesting and egg-laying activity peaks in June. Nesting is highly synchronous across large geographic areas. Females and males start the nest as a scrape in a grassy area, gradually adding grasses and feathers to form a bowl throughout incubation. Females lay from 6 to 14 pale, greenish eggs in a clutch. They lay 1 egg per day until the clutch is complete and begin incubating a day or two before the final egg is laid. Some females lay eggs in the nests of other females. Larger clutches are found in southern populations than in northern populations. Males abandon their female mates on the nest in mid to late June, about mid-way through incubation, which lasts 21 to 27 days. Lesser scaup ducklings that hatch from larger eggs and later in the season have higher survival rates than others. It is thought that lesser scaup breed later in the season than other North American ducks in order to take best advantage of amphipod prey abundance, which increases later in the season. Young can fly 47 to 61 days after hatching. Males and females can breed in the first year after hatching, although breeding may be delayed in unfavorable years. (Austin, et al., 1998; Dawson and Clark, 1996)

  • Breeding interval
    Lesser scaup breed once yearly, they typically lay one clutch, but may attempt a replacement clutch if the first is destroyed early in the season.
  • Breeding season
    Breeding occurs in May and June.
  • Range eggs per season
    6 to 14
  • Average eggs per season
  • Range time to hatching
    21 to 27 days
  • Range fledging age
    47 to 61 days
  • Range time to independence
    2 to 5 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Only females incubate the eggs and care for the young after hatching. Males abandon females during the incubation phase. Young are precocial at hatching and can feed themselves. Females lead their brood away from the nest within a day of hatching. Young feed from the water surface initially, but feed by diving by 2 weeks old. Females attend their brood for 2 to 5 weeks after hatching, often abandoning them before they begin to fly. (Austin, et al., 1998)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • protecting
      • female


Most mortality occurs within the first few weeks of hatching as a result of predation and cold stress. Ducklings that are hatched from larger eggs and later in the season have higher survival rates, so nutrient reserves influence survival. Lesser scaup seem to have a flexible reproductive strategy that allows them to take advantage of temporally variable resources to maximize reproductive success. The maximum recorded lifespan in the wild is 18 years, 4 months. Annual mortality estimates range from 32 to 71%. (Austin, et al., 1998)

  • Range lifespan
    Status: wild
    18.33 (high) years


Lesser scaup are social, non-aggressive birds. They are tolerant of conspecifics except for the early breeding season, when males defend their female mates. In winter they form large flocks for molting and migration. Flocks as large as 500,000 have been reported. They are active during the day, foraging for about 20 minutes at a time throughout the day. (Austin, et al., 1998)

Home Range

Breeding pairs do not defend territories, instead they have small, overlapping home ranges that change in size throughout the breeding season. Home range sizes are from 26 to 166 hectares. In winter lesser scaup may be somewhat nomadic. Females return to their natal range in subsequent years, males do not. (Austin, et al., 1998)

Communication and Perception

Lesser scaup use a set of visual displays, sometimes accompanied by vocalizations, during courtship. The most common display is called the "cough" because they give a short "whew" sound while they flick their wings and tail. Males also use a head-throw and kinked-neck display to attract females. Lesser scaup are fairly quiet animals. Males give a soft call during courtship and a whistle during mating displays that accompanies their visual display. Females also make a soft "arrr" sound during courtship, which signals her interest in a particular male. Females make a "purrrr" call that is directed towards predators and is also used to attract the help of their male mates when they are flying from the nest to a pond. Males then keep other males away that might harass the female. (Austin, et al., 1998)

Food Habits

Lesser scaup adults and young eat insects, crustaceans, and mollusks. They sometimes also take the seeds of aquatic plants, such as yellow pond lily (Nuphar). They forage in shallow, open water by diving. They dive at an angle and surface a few meters from where they dived. They mostly eat prey underwater, but will bring larger prey to the surface to handle it there. Diet varies with the seasonal availability of food and regionally. In breeding lakes amphipods are especially important in the diet. Midges (Chironomidae) and leeches (Hirudinea) are also important in northern lakes. Mollusks and plant seeds become more important at other times of the year and fish and their eggs are taken opportunistically. Seeds become more important in the diet in fall.

  • Animal Foods
  • fish
  • eggs
  • insects
  • mollusks
  • terrestrial worms
  • aquatic crustaceans
  • Plant Foods
  • seeds, grains, and nuts


Ducklings that are attacked by predators try to stay together and females will try to protect their young, but often their defenses aren't sufficient. Females try to keep their young near the cover of vegetation and the cryptic coloration of ducklings may help to protect them. Adults may feign death when taken by large predators. Most predation is on eggs and hatchlings. Eggs are taken by American mink, raccoons, red foxes, American crows, ring-billed gulls, California gulls, common ravens, and American badgers. Ducklings are taken by many of the same predators, as well as black-billed magpies, great horned owls, black-crowned night herons, Swainson's hawks, American coots, and Arctic loons. Adults are taken by the terrestrial predators mentioned, along with striped skunks and coyotes, when on the nest. Adults are also taken by snapping turtles, red-tailed hawks, peregrine falcons, snowy owls and bald eagles. (Austin, et al., 1998)

Ducklings that are attacked by predators try to stay together and females will try to protect their young. Females try to keep their young near the cover of plants and the dull brown feathers of ducklings may help to protect them. Adults may pretend to be dead when attacked by large predators. Most predation is on eggs and hatchlings. Eggs are taken by American mink, raccoons, red foxes, American crows, ring-billed gulls, California gulls, common ravens, and American badgers. Ducklings are taken by many of the same predators, as well as black-billed magpies, great horned owls, black-crowned night herons, Swainson's hawks, American coots, and Arctic loons. Adults are taken by the other mammal predators mentioned and striped skunks and coyotes when they are on the nest. Adults are also taken by snapping turtles, red-tailed hawks, peregrine falcons, snowy owls and bald eagles.

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Lesser scaup are important predators of aquatic invertebrates in northern boreal lakes. Eggs and hatchlings are taken by a wide range of terrestrial, avian, and aquatic predators. They are susceptible to a range of diseases and parasites. Recorded diseases include avian influenza A, avian cholera (Pasteurella multocida), avian botulism, and aspergillosis (Aspergillus fumigatus). Lesser scaup host a number of scaup specific helminth parasites, including, including gizzard worms (Streptocara crassicauda). Other parasites include renal coccidia (Eimeria species), blood parasites (Leucocytozoon simondi and Haemoproteus nettionis), and g.Sarcocystis> species. Leeches (Theromyzon rude) are often found on the nasal membranes of lesser scaup.

Lesser scaup nests are parasitized by other lesser scaup as well as by other ducks, including redheads, gadwall, white-winged scoters, ruddy ducks, canvasbacks, and red-breasted mergansers. Lesser scaup also parasitize the nests of other ducks, including gadwall, orthern shovelers, redheads, white-winged scoters, and canvasbacks. (Austin, et al., 1998)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Lesser scaup are important members of North American wetland ecosystems. They are also hunted during migration. (Austin, et al., 1998)

  • Positive Impacts
  • food
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of lesser scaup on humans.

Conservation Status

Lesser scaup are considered least concern by the IUCN because of their large population sizes and geographic range. They are one of the most abundant duck species in North America. However, regional population declines have been documented and some populations may be susceptible to habitat degradation (such as wetland destruction) and pollution. High levels of selenium have been detected in the livers of lesser scaup in the Great Lakes region, but not in other regions where research has been conducted to date. Research on female body condition just prior to egg laying in North America suggests that nutrient stress is resulting in lower reproductive success in North America. (Anteau and Afton, 2004; BirdLife International 2008, 2008; Custer, et al., 2003; Lindeman and Clark, 1999)

Other Comments

Lesser scaup are most closely related to greater scaup (Aythya marila), which are a primarily coastal, maritime species. (Austin, et al., 1998)


Tanya Dewey (author), Animal Diversity Web.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the southern part of the New World. In other words, Central and South America.

World Map


uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

  1. active during the day, 2. lasting for one day.

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.


A substance that provides both nutrients and energy to a living thing.


mainly lives in water that is not salty.


An animal that eats mainly insects or spiders.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


marshes are wetland areas often dominated by grasses and reeds.


makes seasonal movements between breeding and wintering grounds


eats mollusks, members of Phylum Mollusca


Having one mate at a time.


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


generally wanders from place to place, usually within a well-defined range.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

seasonal breeding

breeding is confined to a particular season


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


uses sight to communicate

young precocial

young are relatively well-developed when born


Anteau, M., A. Afton. 2004. Nutrient reserves of lesser scaup (Aythya affinis) during spring migration in the Mississippi flyway: a test of the spring condition hypothesis. The Auk, 121: 917-929.

Austin, J., C. Custer, A. Afton. 1998. Lesser Scaup (Aythya affinis). The Birds of North America Online, 338: 1-17.

BirdLife International 2008, 2008. "Aythya affinis" (On-line). The IUCN Redlist. Accessed April 02, 2009 at http://www.iucnredlist.org/details/141551.

Custer, C., T. Custer, M. Anteau, A. Afton, D. Wooten. 2003. Trace Elements in Lesser Scaup (Aythya affinis) from the Mississippi Flyway. Ecotoxicology, 12: 47-54.

Dawson, R., R. Clark. 1996. Effects of variation in egg size and hatching date on survival of Lesser Scaup Aythya affinis ducklings.. Ibis, 138: 693-699.

Lindeman, D., R. Clark. 1999. Amphipods, land-use impacts, and lesser scaup (Aythya Affinis) distribution in Saskatchewan wetlands. Wetlands, 19: 627-638.