The greater scaup and lesser scaup are two similar-looking species of diving ducks that can be challenging to distinguish in the field. While they overlap significantly in their breeding and wintering ranges across North America, there are some key differences in appearance and behavior that birders can watch for. Paying close attention to details like head shape, bill color, wing stripe and flight profile will help you confidently separate these two scaup species. Read on for an overview of identification tips and tricks for telling greater and lesser scaup apart.
Range and Habitat
Greater and lesser scaup inhabit many of the same regions throughout the year, though their precise distributions differ.
Breeding Range
The breeding range for greater scaup concentrates in the boreal forest wetlands of Alaska and Canada. The lesser scaup’s breeding grounds center more southerly in the prairie pothole region of the northern U.S. and southern Canada.
Wintering Range
In winter, both species migrate from their breeding areas to occupy coastal habitats across much of the lower 48 states. The Pacific and Atlantic coasts see large concentrations of wintering scaup. They also inhabit inland lakes, reservoirs and rivers. Lesser scaup tend to winter farther south than greater scaup on average.
Migration
During migration, greater and lesser scaup follow the Central and Mississippi flyways over the Midwest. Large numbers stop over on the Great Lakes. Watch for mixed flocks of scaup species at mid-latitude inland wetlands in spring and fall.
Year-Round Range
Parts of the upper Midwest and Northeast host both species throughout the year. The Great Lakes and Long Island Sound region are particularly good locations to study differences between breeding, migrant and wintering greater and lesser scaup together.
Identification Tips
Though they occupy roughly the same habitats throughout the year, greater and lesser scaup show some key physical differences that allow an observer to distinguish them in the field.
Head Shape
Pay attention to head profile in frontal views of scaup. The greater scaup has a more rounded, crested crown, giving the head a peaked shape. The lesser scaup has a flatter crown and more angular head outline.
Bill Color
The greater scaup has a blue bill with a black tip and narrow black nail. The lesser scaup’s bill is more uniformly blue-gray with a wider black tip and nail. The lesser’s dark nail is more pronounced.
Wing Stripe
The white wing stripes or bars visible on the secondary feathers in flight and at rest differ between the two scaup species. The greater shows brighter, wider white stripes. The lesser has more muted gray stripes in comparison.
Flight Profile
When flying, the greater scaup shows a more rounded head protruding above a rounder, fuller body shape. The lesser appears flatter-headed with a thinner, more angular body profile in flight.
Size and Shape
The greater scaup is a slightly larger, chunkier duck overall, though the size difference is subtle. The female greater is noticeably larger-bodied than the petite female lesser scaup.
Other Hints
Lesser scaup tend to flock in dense rafts in winter more often than greaters. Listen for the subtly raspy voices of courting males in spring. Greater scaup sound huskier, less whistle-like. Immature lesser scaup show delicate vermiculations on the back feathers.
Similar Species
Some other diving ducks overlap in range with the scaup duo and could potentially cause confusion. Watch for these key differences:
Ring-necked Duck
Drake ring-necks have distinctive white rings around the base of their gray bills and pale rings around the neck. Hens resemble female scaup but are browner overall with a more rounded head shape.
Canvasback
Larger with a blocky head profile, reddish eyes, sloping bill profile and darker back than either scaup species. Both sexes show a distinctive cinnamon head and neck color.
Tufted Duck
Rare vagrant to North America from Eurasia. Male shows yellow eyes and a taller, shaggy crest on the hindcrown.
Bufflehead
Tiny diver with a huge head and tiny bill. Dark iridescent head and white patches on the male. Female small and dainty overall.
Behavioral Differences
Lesser scaup tend to raft in extremely large, tightly packed flocks in winter more often than greaters. Listen for vocalizations – the male greater’s courtship call is a more guttural purring, while the lesser has a higher-pitched whistle. Greater scaup prefer larger, deeper lakes and inland seas during migration while lessers occur more on smaller wetlands and rivers. Watch feeding habits – greaters dive deeper and migrate further north to breed.
Conclusion
Separating the greater and lesser scaup takes practice and attention to subtle details. Look at the head shape, bill color, wing stripes and overall body profiles. Listen for vocalizations and watch flocking behavior. Consider the habitat. With experience, birders can distinguish these lookalikes reliably. Consult field guides and veteran birders for help when unsure. Paying attention to the nuances will sharpen your skills at identifying these two diving ducks by sight and sound.
Trait | Greater Scaup | Lesser Scaup |
---|---|---|
Head Shape | Rounded crown, peaked profile | Flatter head, angular profile |
Bill Color | Blue with black tip and nail | Blue-gray with wider black tip and nail |
Wing Stripe | Bright, wide white stripes | Duller gray stripes |
Flight Profile | Round head, full body | Flatter head, thinner body |
Size | Slightly larger | Slightly smaller |
Voice | Husky purring call | Whistling call |
Winter Flocking | Loose groups | Dense rafts |
Preferred Habitat | Large, deep lakes | Small wetlands and rivers |
Diving Habits | Deeper diver | Shallower diver |
Breeding Range | Far northern boreal forest | Prairie pothole region |
Distribution Maps
Greater Scaup
Image: Greater Scaup range map via All About Birds
Lesser Scaup
Image: Lesser Scaup range map via USFWS
Spotting Scope Field Marks
When viewed through a spotting scope, several subtle field marks can help confirm Greater or Lesser Scaup:
Head Shape
Greater shows a rounder, more domed crown profile while Lesser appears flatter-headed from above.
Bill Profile
From the side, the Greater’s bill has a rounder bulge on top while the Lesser’s is flatter and more evenly tapered.
Wing Stripe
The thin white stripes on the Greater’s wings appear crisper and brighter white compared to the Lesser’s duller gray lines.
Back Feathers
The feather edging on the back and flanks of Greater Scaup is lighter, creating more contrast with the darker feather centers. Lesser shows subtler vermiculations.
Nail
When seen head-on, the Greater shows a smaller nail appearing as just a thin line at the bill tip while the Lesser has a wider, more pronounced nail.
Plumage Variations
Both species show changes in plumage appearance throughout the year and between sexes:
Breeding Males
Drake greater scaup sport a dark green head, white flanks and belly, with a peaked crown and purplish sheen on the neck and sides. Lesser drakes have a purple head, less crisp delineation between dark and light areas, and a more angular head shape.
Non-Breeding Males
In winter, the white portions of the greater’s plumage appear dingier. The purple gloss fades from the head but the distinctive greenish cast remains. The lesser loses most purple highlights outside the breeding season.
Females
Hen greater scaup are noticeably larger-bodied than female lessers. They also tend to show more contrast between the brown head and body and the white neck and belly areas. Female lessers have a more uniform wash of brown throughout.
Immatures
Juvenile scaup resemble females but with vermiculated gray-brown back feathers. This vermiculation is daintier and finer on young lesser scaup compared to the bolder markings on young greater scaup.
Hybridization
In areas where their breeding ranges overlap around the Great Lakes and prairie potholes, greater and lesser scaup occasionally hybridize. The resulting mixed birds tend to show intermediate traits like a purple head, grayish body plumage, extensive vermiculations, and a bill that is mostly blue with a small black tip. Hybrids are rare but can add a wrinkle to identification.
Origin of Names
“Scaup” derives from the Old Dutch term “schep” referring to the mussel-eating habits of these birds. “Greater” and “lesser” denote their relative sizes. “Bluebill” is another common name referring to the blue bill color shared by both species.
Conservation Status
Both scaup species remain common and widespread, though some populations have declined:
Greater Scaup
Greater Scaup populations decreased significantly between the 1980s and early 2000s, though numbers have stabilized more recently. Habitat issues on the breeding grounds and exposure to contaminants may threaten this species’ numbers.
Lesser Scaup
Lesser Scaup have declined more moderately over the past few decades. The conversion of prairie wetlands to agriculture has reduced breeding habitat. Conservation programs aim to restore wetlands across their range.
Key Takeaways
To quickly summarize key differences:
– Head shape: Greater has a rounder, peaked crown; Lesser has a flatter profile
– Bill color: Greater shows blue with thin black band; Lesser has more extensive black
– Wings: Greater displays thicker white stripes; Lesser has thinner gray lines
– Size: Greater averages slightly larger
– Voice: Greater gives a husky purr; Lesser emits a higher whistle
– Habitat: Greater prefers larger, deeper lakes; Lesser likes small wetlands
Study these field marks carefully and with experience you’ll be able to distinguish Greater and Lesser Scaup reliably during all seasons and plumages.