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Species Profile

Lesser Scaup

Aythya affinis

Peaked crown, big rafts, true diver
2009fotofriends/Shutterstock.com

Lesser Scaup Distribution

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This map shows coastal regions where Lesser Scaup are found.

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Found in 52 locations

Lesser scaup resting at lakeside, this is a medium-sized diving duck with a small peak at the back of the head. From the small peak, the back of the head and neck is flat.

At a Glance

Wild Species
Also Known As Bluebill, Little Scaup, Little Bluebill, Scaup
Diet Omnivore
Activity Diurnal+
Lifespan 5 years
Weight 1.09 lbs
Status Least Concern
Did You Know?

Size: 38-48 cm long; wingspan 68-79 cm (adult).

Scientific Classification

The Lesser Scaup is a medium-sized diving duck common across North America, especially on freshwater lakes and coastal waters during migration and winter. It feeds largely on aquatic invertebrates and plant material and is known for forming large rafts on open water.

Kingdom
Animalia
Phylum
Chordata
Class
Aves
Order
Anseriformes
Family
Anatidae
Genus
Aythya
Species
Aythya affinis

Distinguishing Features

  • Small scaup with a rounded head profile that often shows a slight rear peak (variable by posture)
  • Adult male with black head showing greenish/purplish gloss, black breast, and finely vermiculated gray back
  • Blue bill with a black nail at the tip (both sexes), typically narrower than Greater Scaup
  • Often in large flocks on open water; diving behavior typical of Aythya ducks

Physical Measurements

Males and females differ in size

Length
♂ 1 ft 5 in (1 ft 3 in – 1 ft 7 in)
♀ 1 ft 4 in (1 ft 3 in – 1 ft 5 in)
Weight
♂ 2 lbs (2 lbs – 2 lbs)
♀ 2 lbs (1 lbs – 2 lbs)
Top Speed
48 mph
flying

Appearance

Primary Colors
Black Gray White Brown Blue
Secondary Colors
Green Purple Yellow Black
Skin Type Dense waterproof feathers over down; keratin bill; fully webbed feet (palmate) adapted for diving.
Distinctive Features
  • Medium-sized North American Aythya diving duck; typically 38-48 cm long (standard field references).
  • Wingspan commonly ~68-78 cm; compact body with relatively short neck.
  • Mass typically ~0.454-1.089 kg, varying by sex, season, and region.
  • Bill usually narrower than Greater Scaup; black nail often proportionally smaller, but variable.
  • Head shape often peaked toward rear (male), unlike rounder Greaters; shape varies with posture.
  • Back shows fine, tight gray vermiculation; Greaters often appear paler and more boldly barred.
  • Forms large open-water rafts during migration and winter; strong wetland and lake dependence.
  • Dives to forage; diet emphasizes aquatic invertebrates (e.g., amphipods, mollusks) plus plant material (seeds, tubers).

Sexual Dimorphism

Strong sexual dimorphism: males are black-headed with white flanks and a vermiculated gray back, while females are mostly brown with a paler face patch near the bill. Both sexes share a blue-gray bill with a black nail.

♂
  • Glossy black head (often green/purple sheen) and black breast
  • Bright white flanks; pale gray vermiculated back
  • Typically shows rear-peaked head profile in many postures
♀
  • Overall brown body with darker crown and back
  • Pale whitish area around base of bill (often prominent)
  • Plainer, more uniformly brown flanks with less contrast

Did You Know?

Size: 38-48 cm long; wingspan 68-79 cm (adult).

Mass: typically ~0.454-1.089 kg (males average heavier than females).

Longevity: banding records show individuals can reach ~18 years in the wild (rare).

Lesser Scaup often raft in the thousands on open water during migration/winter.

Key field mark vs Greater Scaup: Lesser usually shows a peaked/angled rear crown; Greater looks rounder and "puffier."

Bill ID vs Greater: Lesser's bill averages narrower with a smaller black nail at the tip; Greater's is broader with a larger nail.

Diet shifts seasonally: more aquatic invertebrates (e.g., amphipods, insect larvae) on breeding waters; more mollusks and plant material in winter, including heavy use of mussel beds in some regions.

Unique Adaptations

  • Diving-duck propulsion: large, rear-set feet act like paddles for efficient underwater swimming, trading off easy walking on land for powerful diving.
  • Dense, waterproof plumage and insulating down: supports long periods on cold open water typical of late fall-winter staging.
  • Broad, lamellate bill suited for grasping and manipulating slippery prey (snails, small mussels) and for taking seeds/vegetation when available.
  • High wing loading for fast, direct flight: useful for long-distance migration between boreal breeding wetlands and temperate/coastal wintering waters.
  • Cranial profile as a real ID trait: the species' typical peaked rear crown (especially in males) is a consistent field cue shaped by skull and feathering differences from Greater Scaup.
  • Flexible diet: able to switch between animal prey and plant foods depending on seasonal availability-important in variable wetland and nearshore conditions.

Interesting Behaviors

  • Deep-diving foraging: dives repeatedly to take benthic prey (mollusks, crustaceans, insect larvae) and submerged plant parts; often feeds in groups where prey is concentrated.
  • "Rafting" and synchronized movement: in migration and winter, flocks gather into dense, floating rafts on large lakes and coastal waters, shifting position with wind, waves, and predator pressure.
  • Courtship on water: males perform head throws, short rushes, and calls while staying close to females; pair bonds form before spring migration and persist into early breeding season.
  • Brood and nest strategy: females nest on the ground near wetlands, often in dense cover; ducklings are precocial and leave the nest soon after hatching, feeding themselves while guarded by the hen.
  • Mixed-species flocking: frequently associates with other Aythya diving ducks (e.g., Greater Scaup, Ring-necked Duck, Redhead), especially during migration and winter.
  • Strong site use where food is reliable: wintering birds may return to the same bays/harbors/lake sections when mollusk or plant resources remain abundant.

Cultural Significance

Lesser Scaup (Aythya affinis), called 'bluebill', is a well-known diving duck for hunters and birders. They form large open-water flocks, help show wetland food (invertebrates, mollusks), and are part of flyway harvest traditions and wetland conservation.

Myths & Legends

In Earth-Diver stories from North America, a diving water bird—often a duck or loon—helps other animals bring up earth from under the first waters to make land, tied to diving ducks like scaup.

In many northern and hunting communities (Great Lakes, boreal), the arrival and departure of Lesser Scaup (Aythya affinis), called 'bluebills,' mark seasons, linked by oral history to freeze-up, thaw, and weather on big waters.

Called the Bluebill, the Lesser Scaup (Aythya affinis) became a famous hunting bird in North America for its fast, stiff-winged flight and wary flocks, inspiring camp stories, decoys, and late-season sayings.

Conservation Status

LC Least Concern

Widespread and abundant in the wild.

Population Decreasing

Protected Under

  • United States: Migratory Bird Treaty Act (1918)
  • Canada: Migratory Birds Convention Act (1994) and associated Migratory Birds Regulations
  • United States/Canada: Federal frameworks establishing regulated waterfowl hunting seasons and bag limits under migratory bird agreements

Life Cycle

Birth 9 ducklings
Lifespan 5 years

Lifespan

In the Wild
1–18 years
In Captivity
5–20 years

Reproduction

Mating System Monogamy
Social Structure Socially Monogamous
Breeding Pattern Seasonal
Fertilization Internal Fertilization
Birth Type Internal_fertilization

Pairs form on wintering grounds; one male typically associates with one female through spring migration and early nesting. Copulation is internal; males usually desert at incubation, leaving females to incubate and brood alone; extra-pair matings can occur.

Behavior & Ecology

Social Flock Group: 300
Activity Diurnal, Crepuscular
Diet Omnivore Benthic mollusks, especially mussels (including invasive zebra and quagga mussels where available)
Seasonal Migratory 1,553 mi

Temperament

Strongly social outside breeding; dense rafts common on lakes and coastal bays (Birds of the World: Lesser Scaup).
More territorial and aggressive at nest sites; females defend immediate nest area against conspecifics.
Generally tolerant within flocks, with brief threat displays around food concentrations.
Seasonal segregation by sex can occur in nonbreeding periods; large single-sex concentrations reported at some sites.
HUBS pattern: flocking intensity peaks during migration/winter; shifts to pairs and dispersed nesting in boreal wetlands.

Communication

Male courtship whistle (short, clear whistled notes) used in pair formation and displays.
Female raspy growls/grunts and scolding calls, especially when disturbed near brood or nest.
Alarm notes are short, harsh calls given during flushing and predator response.
Courtship displays: head-throw, neck-stretch, and swimming postures; synchronized movements in groups.
Visual threat displays: bill pointing and head pumping during close-range disputes at feeding areas.
Contact maintenance via proximity and following behavior within broods and tight winter rafts.

Habitat

Lake Pond River/Stream Wetland Marsh Bog Estuary Coastal Open Ocean Urban Agricultural/Farmland +5
Biomes:
Freshwater Wetland Marine Boreal Forest (Taiga) Temperate Grassland Temperate Forest
Terrain:
Riverine Coastal Plains Valley Muddy Sandy
Elevation: Up to 8202 ft 1 in

Ecological Role

Benthic consumer (invertebrate predator) and secondary seed consumer/disperser linking aquatic vegetation/benthos to higher trophic levels in freshwater and coastal ecosystems.

Regulation of benthic invertebrate populations (including mussels and insect larvae) Bioturbation and nutrient cycling via benthic foraging and excretion Seed movement/dispersal of aquatic plants through ingestion and transport Energy transfer to predators (raptors, mammals) as a common prey species in aquatic food webs

Diet Details

Main Prey:
Mussels and clams Aquatic snails Amphipod Midge Caddisfly larvae Mayfly nymph Dragonfly and damselfly nymphs Aquatic beetle Crayfish +3
Other Foods:
Pondweed seeds and submerged aquatic vegetation Wild celery Widgeongrass Bulrush seeds Sedge seeds Smartweed seeds Aquatic plant seeds and vegetative parts +1

Human Interaction

Domestication Status

Wild

Lesser Scaup (Aythya affinis) is a wild, migratory North American diving duck with no history of domestication or being bred by people. It breeds in boreal and prairie-parkland areas and winters on large inland lakes and coasts. People only keep it under rules for rescue care, research, education, or zoos. Humans also hunt, manage habitat, and band it.

Danger Level

Low
  • Physical injury is uncommon; potential minor scratches/bites if handled (e.g., during rescue/banding).
  • Zoonotic risk is low but non-zero when handling wild waterfowl or contaminated water: potential exposure to avian influenza viruses and other enteric pathogens; risk is primarily to handlers without PPE and is managed by standard wildlife-handling hygiene.
  • Lead/contaminant exposure risk is indirect: scaup can carry ingested lead shot or accumulated contaminants; the human risk is mainly via consumption of improperly processed harvested birds in contaminated areas.

As a Pet

Not Suitable as Pet

Legality: Keeping a Lesser Scaup as a pet is usually illegal in the U.S. and Canada without federal, provincial, or state permits (e.g., science, rehab, or education). Other countries often require permits and biosecurity rules.

Care Level: Expert Only

Purchase Cost:
Lifetime Cost: $15,000 - $60,000

Economic Value

Uses:
Recreational hunting value (regulated harvest) Subsistence/food value in some regions Ecotourism and birdwatching Ecosystem services indicator (wetland health; monitoring/assessment) Research value (migration ecology, contaminants, disease surveillance)
Products:
  • meat from legally harvested birds
  • non-market services: recreation (waterfowl hunting, birding), cultural value
  • scientific data (banding recoveries, contaminant datasets)

Relationships

Predators 10

Bald Eagle
Bald Eagle Haliaeetus leucocephalus
Golden Eagle
Golden Eagle Aquila chrysaetos
Peregrine Falcon
Peregrine Falcon Falco peregrinus
Great Horned Owl Bubo virginianus
Gyrfalcon Falco rusticolus
Mink
Mink Neogale vison
North American River Otter
North American River Otter Lontra canadensis
Red Fox
Red Fox Vulpes vulpes
Raccoon
Raccoon Procyon lotor
American Crow Corvus brachyrhynchos

Related Species 10

Greater Scaup Aythya marila Shared Genus
Ring-necked Duck Aythya collaris Shared Genus
Canvasback
Canvasback Aythya valisineria Shared Genus
Redhead Aythya americana Shared Genus
Tufted Duck Aythya fuligula Shared Genus
Common Pochard Aythya ferina Shared Genus
Ferruginous Duck Aythya nyroca Shared Genus
Bufflehead Bucephala albeola Shared Family
Common Goldeneye
Common Goldeneye Bucephala clangula Shared Family
Common Merganser Mergus merganser Shared Family

Ecological Equivalents 5

Animals that fill a similar ecological role in their ecosystem

Greater Scaup Aythya marila Both species dive in open water, form large rafts, and eat many invertebrates (mollusks and crustaceans); in the Great Lakes they use dreissenid mussels. The Lesser Scaup is slightly smaller and uses more freshwater inland areas.
Ring-necked Duck Aythya collaris Similar foraging mode (diving) and habitat use (freshwater lakes, ponds, and marshes), with substantial diet overlap in aquatic invertebrates and some submerged vegetation. Frequently occurs in mixed-species flocks with scaup during migration and winter (Birds of the World).
Bufflehead Bucephala albeola Fills a similar role as a small diving duck in freshwater and nearshore marine areas, feeding on aquatic insects, crustaceans, and mollusks. Often winters with other small diving ducks, favors smaller waters, and nests in cavities.
Ruddy Duck
Ruddy Duck Oxyura jamaicensis Another diving duck commonly using freshwater basins and feeding heavily on aquatic invertebrates and plant material; shares the behavior of foraging underwater and staging in open-water flocks/rafts, though it has different morphology (stiff-tailed) and is often more marsh-focused in habitat.
American Coot Fulica americana Not a duck but frequently shares the same lakes, reservoirs, and wintering areas; overlaps in consumption of aquatic vegetation and some invertebrates; and can occur in large open-water aggregations alongside scaup.

Lesser Scaup Summary

Young lesser scaups learn to dive as soon as their down dries.

The lesser scaup is a medium-sized diving duck. They are often seen forming groups with other species of diving ducks, such as canvasbacks and the greater scaup. Spending some of their earliest moments on the water, lesser scaups will sleep, eat, and socialize on the water. Unlike dabbling duck species, they can dive up to several feet underwater to secure their prey.

Lesser Scaup Amazing Facts

  • Of all the duck species to migrate, the lesser scaup is often one of the last to make the move either north or south. 
  • They can be found in almost all types of waters, including coastal bays and estuaries. 
  • Their habitats range from as far north as Alaska down into South America. 
  • These ducks typically migrate at night. 
Lesser Scaup bird infographic

Where to Find Lesser Scaups

Lesser scaups can be found throughout the western hemisphere. During their breeding season, they can be found in the far northern region of North America, including in Alaska. Outside of the breeding season, they live in the southernmost region of the United States, Mexico, Central America, and the Caribbean. They can be seen throughout the rest of the United States during their migratory period, and there are a few year-round populations in the United States and Venezuela. 

During the breeding season, they prefer fresh and brackish wetlands. However, they favor any water source during the rest of the year. This includes common freshwater sources like lakes and ponds as well as coastal waters. 

Lesser Scaup Nests

Lesser scaups will make their nests on the ground. They prefer to nest along tall vegetation in prairies and wetlands. Sometimes, females will choose to build their nests on floating platforms. No matter where they build it, however, they will always ensure that they conceal their nests well among the vegetation. 

In order to build their nests, female lesser scaups will make a small depression in the ground. This will serve as the foundation for the nests. Then, they will begin to add grass and other plants, as well as down feathers.

Sometimes, you may see a half-completed nest with eggs. This is because female lesser scaups will lay their eggs before finishing the nest, and then they will finish the nest around their brood. 

Lesser Scaup Scientific Name

The lesser scaup is in the class of Aves. There are in the Order Anseriformes and Family Anatidae. Their genus name is Aythya. This includes twelve different species of ducks. Their scientific name is Aythya affinis.

Their genus name is derived from the ancient Greek word aithuia. This is an unidentified seabird that appeared in many of the popular writings of the time period. Their species name comes from the Latin affinis, or related to, because of their similarities to the greater scaup.

Lesser Scaup Size, Appearance & Behavior

Male Lesser Scaup in Flight

Lesser scaup have a wingspan of 27 to 31 inches.

©Brian E Kushner/Shutterstock.com

Adults grow 15 to 19 inches long on average. They can weigh 1.0 to 2.5 pounds, with males typically being heavier than females in the species. Their wingspan is 27 to 31 inches. 

Adult males have dark black plumage. They have some white markings along their wings and backs. You can identify females by their brown coloration and the thick wide band at the base of their bills. 

This species is also known as the little bluebill or just broadbill. This is because they have a distinctive blue bill. 

They are not extremely vocal, especially compared to species of dabbling ducks. However, males do have distinct mating calls, with females having similar responses. As a result, mating time is typically the loudest season for these ducks, especially as their young come into the world with their own calls. Their name comes from the female’s call, which sounds like scaup, scaup. 

Migration Pattern and Timing

Lesser scaups are some of the last ducks to migrate each season, both to and from the breeding grounds. They are nighttime migrators who tend to only travel a medium distance each year. 

Most populations will spend the winter months around the Gulf of Mexico. However, there are some individuals who prefer to migrate further south. 

Lesser Scaup Diet

Like many other species of diving ducks, they are omnivorous. The majority of their diet consists of aquatic invertebrates. However, they will also eat aquatic seeds and plants. Although they dive for their food, they usually forage in waters less than sixteen feet deep. 

What does the lesser scaup eat?

This duck will eat mussels, clams, leeches, insects, and snails. The main plants in the vegetative portion of their diet are aquatic sedges and grasses. 

Lesser Scaup Predators and Threats

Lesser scaups and their nests are vulnerable to many different threats, including predation. In recent years, they have faced a decline in population. However, while they are many theories as to the cause of this decline, there have been no studies able to confirm these. Some of the probable causes include climate change, hunting, limited resources during migration, and changes in geography. 

There are also many predators for adult, young, and unborn individuals. These may vary based on the area that the individual settles, but many are present nonetheless. 

What eats the lesser scaup?

One of the most notable predators of the lesser scaup is the red fox. This species will prey on adults, young, and eggs in the nest. They will also hunt adults outside of breeding season whenever they come ashore. Predators on land include snakes, raccoons, and mink. They may also fall prey to other birds, such as red-tailed hawks and owls.

Lesser Scaup Reproduction, Babies, and Lifespan

Lesser scaups are monogamous throughout the season, although they may find a different mate the next year. Once they navigate to the breeding ground and build their nest, they will typically have only one brood. These broods will contain anywhere from six to 14 eggs.

Each egg is around 2.2 inches long and 1.5 inches wide. The shell is pale olive to slightly green in color. 

The incubation period lasts from 21 to 27 days. Once hatched, the young will be born with down and their eyes open. They are ready to leave the nest within 24 hours.

Lesser Scaup Population

There are around 3.7 million lesser scaup individuals in the world. Although their population has declined, there are measures put into place to help protect this species. This includes the Conservation Reserve Program (CRP), which is working to protect nesting habitats. 

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Sources

  1. https://www.fsa.usda.gov/programs-and-services/conservation-programs/conservation-reserve-program/
Megan Martin

About the Author

Megan Martin

Megan is a writer at A-Z Animals where her primary focus is birds, felines, and sharks. She has been researching and writing about animals for four years, and she holds a Bachelor of Arts in English with minors in biology and professional and technical writing from Wingate University, which she earned in 2022. A resident of North Carolina, Megan is an avid birdwatcher that enjoys spending time with her cats and exploring local zoological parks with her husband.

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Lesser Scaup FAQs (Frequently Asked Questions)

Yes, lesser scaups migrate twice a year. They spend breeding season in the northern part of their range and winters in the south.

View Lesser Scaup Photos