Greater Scaup vs Lesser Scaup

In short

The Greater Scaup (Aythya marila) and Lesser Scaup (Aythya affinis) are two closely related diving ducks that can be challenging to differentiate. Key differences include size, with the Greater Scaup generally being larger, and plumage details, such as the shape of the head and the presence of distinct markings on the bill. Understanding these nuances is essential for accurate field identification.

Identification tips

1. Birds of the World Similar-Species Diagnostics:

2. "The Greater Scaup tends to be larger, has a more rounded head, and a more pronounced white wing patch compared to the Lesser Scaup." (Source: Birds of the World - Greater Scaup, Similar Species section)

3. AI Field Diagnostics:

4. Size: Look for size differences; the Greater Scaup is noticeably larger than the Lesser Scaup. A quick comparison can be made by observing flock sizes – if they seem to differ greatly, they might be of different species.
5. Head Shape: Pay close attention to head shape. The Greater Scaup has a rounder head, while the Lesser has a flatter crown. This is particularly noticeable when the ducks are swimming or resting.
6. Plumage Patterns: Observe the color and contrast of the plumage. The Greater Scaup's male has a darker, more vibrant green head compared to the Lesser’s purplish sheen. The black breast of the Lesser is also a distinguishing feature against its lighter body.
7. Wing Patches: In flight, the white wing patch of the Greater Scaup is more expansive and visible compared to the Lesser’s, which is smaller and less pronounced.
8. Foraging Behavior: If you see a scaup diving deeply, it's more likely to be a Greater Scaup, whereas a scaup that is dabbling or foraging near the surface is likely a Lesser.
9. Habitat: Note the habitat; if you are in a smaller pond or marshy area, you are more likely to encounter Lesser Scaup, while larger lakes or coastal waters may host Greater Scaup.

By applying these identification tips, birdwatchers can enhance their ability to distinguish between these two similar species effectively.

Size

• Greater Scaup: Larger overall, averaging about 15-21 inches (38-53 cm) in length and weighing 1.5-2.5 pounds (680-1134 g).
• Lesser Scaup: Smaller, typically measuring 14-19 inches (36-48 cm) in length and weighing 1-2 pounds (450-910 g).

Plumage

• Greater Scaup: Adult males have a dark green head with a slightly rounded crown, a white body with a blackish back, and a distinct white wing patch that is more prominent in flight.
• Lesser Scaup: Males have a more iridescent purple head with a flatter crown, a blackish breast, and a lighter grayish body compared to the Greater. The wing patch is also white but less pronounced than that of the Greater Scaup.

Behaviour

• Greater Scaup: Often forages in deeper waters and can be seen diving for food. They are more social and tend to form larger flocks compared to the Lesser Scaup.
• Lesser Scaup: Prefers shallower waters and often forages near the surface, making them more likely to be seen dabbling. They are generally more solitary or found in smaller flocks.

Habitat

• Greater Scaup: Typically found in large lakes, rivers, and coastal bays, particularly during migration. They prefer deeper waters.
• Lesser Scaup: Commonly found in smaller ponds and marshes, favoring shallower habitats with abundant aquatic vegetation.

Voice

• Greater Scaup: Males have a distinctive "scaup" call, while females produce a series of quacks and whistles.
• Lesser Scaup: Males have a softer, less pronounced "whistling" call, while females also produce quacks but are less vocal than Greater Scaup females.