These two very similar ducks share similar plumage features and only vary slightly in size, with Greater Scaup being slightly larger. Careful assessment of their subtle head shape and neck thickness differences will eventually lead to a recognition of these differences, even with single birds. While Greater Scaup has a bigger bill on average, the smaller head and thinner neck of Lesser Scaup may give you the impression of it having a relatively large bill like a Greater.

 

Physical Features:

Greater Scaup is slightly larger than Lesser Scaup and has a more rounded head shape with a peak closer to the front of the crown. Some Greaters may show a bump on the front and rear crown, but its lower profile, evenly rounded head shape differs from Lesser, which has a taller, narrower head with a peak near the rear of the crown. The slimmer head of Lesser also shows a noticeable slope to the rear crown below the peak. Be aware that these features vary depending on the duck’s behavior, and are best evaluated on relaxed birds. Lesser also gives the impression of having a longer, thinner neck than Greater, but this feature is best assessed on birds who have their necks raised.

 

Greater Scaup has a larger, wider bill that has a more prominent dark nail at the tip, while Lesser has a slightly smaller, thinner, straighter bill with a less prominent black nail that may be hard to see due to its small size. 

 

Plumage and Bare Parts Details:

Greater Scaup tends to have heavier, coarser dark barring on the back than Lesser, but we find this feature hard to determine and not very helpful in the field. While Greater usually shows a greenish gloss to the head and neck and Lesser a purple gloss, both can show a mix of these colors depending upon the light. However, in even light, these color differences can be somewhat reliable.