Greater Scaup vs Lesser Scaup: What Are The Differences?

The Lesser Scaup (Aythya affinis) and Greater Scaup (A. marila) are two closely related North American diving duck species in the Aythya genus. At least one of these medium-sized waterfowl species can be seen just about anywhere between Alaska in the north and Florida in the South.

These two birds can be really tough to distinguish where they occur together, so how do birdwatchers tell them apart?

You can tell the difference between Greater and Lesser Scaups by comparing their head shape. Greater Scaups have a rounded crown, while the feathers on the Lesser Scaups’ head form a slight bump or crest towards the rear. When seen in flight, Greater Scaups have a white stripe on their wings that extends from the secondaries and onto the primary flight feathers. In the Lesser Scaup, this stripe fades onto the primaries.

Greater Scaup

Lesser Scaup

Apart from these differences, male Greater Scaups have whiter flanks than male Lesser Scaups, and female Greater Scaups can have more extensive white plumage on their face than their close relatives. Making an accurate identification presents birdwatchers with a great challenge, even more so when you see the birds at longer distances.

Greater and Lesser Scaups are gregarious birds that can gather in groups of hundreds or even thousands in suitable habitats. The two species do not usually form mixed flocks where they occur together.

You can spot these two diving ducks at some of the same large inland water bodies, but for the most part, Greater Scaups are winter visitors to the coastline of the USA, and Lesser Scaups are more common at inland wetlands and lakes.

Read along to learn more about the differences between Greater and Lesser Scaups.

Close up of a Greater Scaup

Which is bigger, a Greater Scaup or a Lesser Scaup?

Greater and Lesser Scaups are very similar in size. Predictably, The Greater Scaup is the larger of the two. Read on to see how these two North American ducks compare.

Greater Scaup measurements

• Greater Scaups measure 15.3 to 22.1 inches ( 39 - 56 cm) in length.
• They have a mass of 25.6 to 48.0 ounces (726 - 1360 g).
• Their wingspan measures 28.4-31.1 inches (72 - 79 cm) from wing tip to wing tip.

Lesser Scaup measurements

• Lesser Scaups have a body length of 15.3 to 18.1 inches (39-46 cm).
• They weigh 16.0 - 38.4 ounces (454-1089 g).
• Lesser Scaups have a wingspan of between 26.8 and 30.7 inches (68-78 cm).

As you can tell, size is not the best field marker for distinguishing between the two species because there is so much overlap. Continue reading to learn which of these two ducks you are more likely to spot.

Close up of a Lesser Scaup

Which is more common, Greater Scaups or Lesser Scaups?

The Lesser Scaup is far more common than the Greater Scaup and has a much wider distribution in the United States than its slightly larger relative. Lesser Scaups can be seen in any of the lower 48 states, to the north in Canada and Alaska, and south as far northern South America.

Greater Scaups are northern birds that breed from Alaska and across the north of Canada. In the winter, these migratory waterfowl head south to marine waters in the Atlantic and Pacific Oceans. They also overwinter on some large inland waterbodies like the Great Lakes.

Close up of a female Greater Scaup

Other differences between Greater Scaups and Lesser Scaups

The most obvious differences between Greater and Lesser Scaups are visible in their head shape and plumage. Listening to their calls and noting their habitat are also great clues for making an identification. Read on to learn which differences to look for.

Head Profile

Head shape is probably the best field marker for distinguishing between these two very similar waterfowl. Lesser Scaups have a small tuft or bump at the top of their heads. Greater Scaups have a larger and more rounded head in comparison.

This bump on the head of the Lesser Scaup is visible towards the back of the head, and the overall head shape is somewhat egg-like. Be aware, however, that these birds tend to flatten their crown just before diving or when otherwise active.

Female Lesser Scaup

Bill Shape

Differences in bill shape between the two species are relatively minor, but every bit counts when trying to distinguish between these two tricky species! Lesser Scaups have a slightly shorter bill, with a concave profile along the top edge. The Greater Scaups’ bill widens towards the tip and looks broader when seen from the front.

Habitat

Sometimes it’s easy to get a pretty good idea of the identity of a Scaup without getting a close look at the bird. That’s because these birds tend to prefer different habitats.

Greater Scaups prefer marine environments in the non-breeding season, although they are also frequent visitors to the Great Lakes. Lesser Scaups are more at home on shallow freshwater bodies, although they also use estuaries and other brackish environments.

A flock of Greater Scaup

Calls

The females of both species are more vocal than the males, producing harsh grunting or barking calls. Male scaups call while displaying, although the male Lesser Scaup is generally silent. When you do hear it, however, the call of the male Lesser Scaup is a brief wee-o, while the call of the male Greater Scaup is a more drawn-out buzzed whistle.

Lifespan

Banding studies have shown that these two diving ducks live to similar ages in the wild. Greater Scaups have been recorded at over 22 years of age, and the oldest known Lesser Scaup lived to over 18 years.

A small flock of Lesser Scaup

Plumage Differences

Lesser and Greater Scaups have practically identical plumage. The iridescent head sheen on the male Lesser Scaup tends to be more purple while the male Greater Scaup looks greener.

Head color can be helpful, but either species can show either color, depending on the quality and angle of light. Differences in the color of the wings are a more reliable indicator.

Continue reading to learn more about these wing plumage differences.

Flanks

The color of the flanks (sides) of swimming or standing Scaups is another helpful tool for making a solid identification. Male Greater Scaups have practically pure white flanks, while the flanks of the male Lesser Scaup are marked in fine vermiculations, creating a dirty gray appearance.

Female and male Greater Scaups in flight

Wings in flight

When seen in flight, both species have a white stripe along the upper side of the wing. In the Lesser Scaup, this white stripe is prominent across the secondaries but does not reach the primaries, becoming brownish instead. The white wing stripe is better developed on Greater Scaups, extending closer to the body and far into the primary feathers.

Lesser Scaup in flight

Female Greater Scaup vs female Lesser Scaup

The females of both species are mostly chocolate brown, with a black bill and yellow eyes. Both species also have white plumage around the base of the bill, although it is not always present on all female Lesser Scaups. The differences in head and bill profiles mentioned above are the most valuable field marks when distinguishing between female Lesser and Greater Scaups.

Juvenile Greater Scaup vs juvenile Lesser Scaup

It is particularly tough to tell juvenile Greater and Lesser Scaups apart. Birders should look for the same differences in head profile, habitat, and distribution that apply to the adults. Both species tend to gather in flocks of their own species, so look out for adult males nearby to help strengthen your identification.