Aythya affinis
lesser scaup

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, Custer, and Afton, 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, Custer, and Afton, 1998; Lindeman and Clark, 1999)

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, Custer, and Afton, 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, Custer, and Afton, 1998)

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, Custer, and Afton, 1998)

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, Custer, and Afton, 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, Custer, and Afton, 1998)

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, Custer, and Afton, 1998)

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.

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, Custer, and Afton, 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.

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, Custer, and Afton, 1998)

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

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

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)

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