Labrador ducks were known almost entirely from wintering birds shot along the coast between Nova Scotia and Chesapeake Bay. They were sold in New York markets, though reportedly considered poor eating. Summer records are absent, and the breeding range is presumed to have been somewhere in Labrador or northern Quebec without a single confirmed nest to support it.
The bill is the most distinctive feature: broad, flattened towards the tip, with soft flaps along the edges and numerous lamellae. This anatomy suggests specialised feeding on small shellfish and other soft prey filtered from sandy bottoms, a narrower diet than most sea ducks.
Why it vanished remains unexplained. It was never abundant in the record, so a small population may already have been at risk. Proposed pressures include shooting, egg and down collection at the unknown breeding grounds, and the heavy nineteenth-century harvest of the shellfish beds it may have depended on. The last widely accepted record is of a bird shot in 1878, and roughly fifty skins are all that remains.