The lesser scaup and greater scaup are two closely related species of diving ducks belonging to the genus Aythya. They are very similar in appearance, which can make differentiating between them challenging for amateur bird watchers. One of the key physical differences between the two species lies in their beaks. While subtle, the variation in beak morphology between lesser scaup and greater scaup is an important identifying feature.
Beak Size and Shape
In general, the most noticeable difference between the beaks of lesser scaup and greater scaup is that the greater scaup’s beak tends to be taller and more convex at the top. The beak of the male greater scaup also tends to be darker blue at the base.
More specifically, the lesser scaup bill averages around 1.8 inches long for males and 1.7 inches long for females. The greater scaup’s bill is slightly larger, averaging around 2 inches long in males and 1.9 inches long in females. While only a subtle difference, the greater scaup’s larger bill size is noticeable when observing the two species side-by-side.
In addition to being slightly longer, the greater scaup’s bill also tends to be more bulging or convex on top. The lesser scaup’s bill has a flatter profile. This curved shape of the greater scaup’s upper mandible gives it a more pronounced hooked look when viewed in profile.
Bill Color
The bill color also differs somewhat between male lesser scaup and greater scaup. The lesser scaup male has a blue-gray bill, while the greater scaup male’s bill is more of a deep blue or purplish-blue at the base where it meets the head. This purplish-blue base color is most vibrant during the breeding season.
Female lesser scaup and greater scaup have more similar bill colors. Both have dull blue-gray bills that can appear nearly black in some lighting conditions. The slightly larger, more curved bill of the female greater scaup is the best way to distinguish them from their lesser scaup counterparts.
Bill Shape Adaptations
The subtle differences in scaup beak size and shape are likely adaptations for their dietary habits. Both species eat mainly mollusks, aquatic insects, fish eggs, and aquatic plants. However, the greater scaup favors mollusks more heavily than the lesser scaup. The larger, more convex upper mandible of the greater scaup allows them to more easily feed on hard-shelled organisms like snails, mussels, and clams.
The lesser scaup’s smaller, flatter bill is likely more efficient for straining tiny food items like insect larvae and plant material from the water. So while adapted for the same general dietary lifestyle, the scaups’ bills have nuanced differences that reflect their slightly varied feeding preferences.
Identifying In Flight
When scaup are flying overhead, the differences in bill size and shape are harder to discern. In these situations, look for key plumage differences on the head and back. The head of the male greater scaup is more purple-glossed and the back appears a darker black. The lesser scaup male has a green-glossed head and grayer back by comparison.
For females, the greater scaup also shows more white around the base of the bill and on the face. Focusing on head plumage and facial patterns is the most reliable way to identify flying scaup if you can’t clearly see their bills.
Geographic Distribution
The habitats and geographic distributions of lesser and greater scaup also offer clues for proper identification. Lesser scaup predominantly breed in the boreal forest lakes of Alaska and Canada. They winter along both coasts of the U.S., favoring coastal estuaries and bays. Greater scaup nest further north in the tundra lakes of Alaska and Canada and scatter more widely across North America for winter.
If you observe a large flock of scaup on the Atlantic or Pacific coasts, chances are they are lesser scaup. Seeing scaup on a small inland pond or lake, especially in northern states, likely indicates greater scaup. Understanding their core habitats can provide context clues about which species you are observing when other visual differences are difficult to discern.
Conclusion
While the lesser scaup and greater scaup appear remarkably similar at first glance, a sharp eye can discern subtle but important differences, particularly in their bill morphology. The greater scaup’s taller, rounder upper mandible contrasts with the flatter, more evenly tapered bill profile of the lesser scaup. Color variation at the bill base provides another useful clue.
Combining bill traits with plumage and distribution patterns allows even amateur birders to reliably distinguish between these remarkably similar diving ducks. So next time you find yourself stumped by a flock of scaup, take a closer look at the details of their bill size, shape, and coloration to determine if they are lesser or greater.
Trait | Lesser Scaup | Greater Scaup |
---|---|---|
Bill Length – Male | 1.8 inches | 2 inches |
Bill Length – Female | 1.7 inches | 1.9 inches |
Bill Shape | Flatter profile | Convex upper mandible |
Bill Color – Male | Blue-gray | Purplish-blue base |
Bill Color – Female | Blue-gray | Blue-gray |
Favored Food Source | Insects and plants | Mollusks |
Primary Breeding Habitat | Boreal forest lakes | Tundra lakes |
Wintering Habitat | Coastal bays and estuaries | Widespread inland |