Lesser Scaup

The Lesser Scaup is one of the most abundant and widespread diving ducks in North America. Known colloquially as the "bluebill," this gregarious species is famous for forming exceptionally large wintering flocks, or rafts, that can number in the thousands. Though superficially similar to its close relative, the Greater Scaup, the Lesser Scaup is slightly smaller, prefers interior freshwater bodies over coastal marine waters during the breeding season, and exhibits subtle but distinct anatomical differences in head shape and wing patterns.

Identifying the Lesser Scaup requires careful attention to head shape and plumage details, as it is easily confused with the Greater Scaup.

Key Field Marks

• Head Shape: The most reliable field mark is the head profile. The Lesser Scaup has an egg-shaped head with a distinct, subtle peak or tuft at the top-rear of the crown, creating a slightly angular silhouette.
• Breeding Male: Features an iridescent dark head that typically shows a purplish sheen in good light (though it can occasionally look greenish), a black chest, a finely barred grey-and-white back (vermiculation), and clean white flanks. The bill is a pale bluish-grey with a tiny black spot at the very tip (the nail).
• Female: Drab brown overall with a prominent white patch surrounding the base of the bill, similar to other scaups but with a more constrained area.
• In Flight: Look for a white wing stripe (speculum) that is restricted to the secondaries (inner wing) and does not extend significantly into the outer flight feathers (primaries), which helps distinguish it from the Greater Scaup.

Lesser Scaups occupy different habitats depending on the season, migrating extensively across North America.

• Breeding Season: They breed primarily in the boreal forests, subarctic regions, and the prairie pothole region of Canada and Alaska. They prefer shallow, freshwater wetlands, marshes, and ponds with abundant emergent vegetation for nesting cover.
• Wintering Season: During winter, they migrate south to the southern United States, Mexico, Central America, and the Caribbean. While they can be found in coastal estuaries and brackish bays, they are much more likely than Greater Scaups to utilize inland freshwater lakes, reservoirs, and agricultural wastewater ponds.
• Migration: They are late-autumn migrants, often waiting until freeze-up to move south, traveling in large, high-altitude V-formations.

Lesser Scaups are highly social ducks that spend most of their time on open water.

Feeding and Diving

These ducks are adept divers, propelling themselves underwater using their large, webbed feet with their wings held tightly against their bodies. They feed primarily by diving to the bottom of shallow water bodies, where they sift through mud and vegetation for aquatic snails, clams, insect larvae, amphipods, and the seeds of pondweeds and wild celery.

Vocalizations

Lesser Scaups are generally silent outside of the breeding season. During courtship, males make a soft, wheezy whistle, while females produce a harsh, low-pitched growling "scaup, scaup" call when startled or communicating with their young.

Nesting

Nests are built exclusively on the ground, often on islands or near the edges of lakes hidden in dense grasses, sedges, or brush. The female scrapes a shallow depression, lines it with grasses and down feathers plucked from her own breast, and lays a clutch of 8 to 14 olive-brown eggs.