Yet another common name was sand shoal duck, referring to its habit of feeding in shallow water.

[8] A mitogenomic study of the placement of the Labrador duck found the species to be closely related to the Steller's eider as shown below.

[11] The Labrador duck migrated annually, wintering off the coasts of New Jersey and New England in the eastern United States, where it favored southern sandy coasts, sheltered bays, harbors, and inlets, and breeding in Labrador and northern Quebec in the summer.

The Labrador duck fed on small molluscs, and some fishermen reported catching it on fishing lines baited with mussels.

[12] The structure of the bill was highly modified from that of most ducks, having a wide, flattened tip with numerous lamellae inside.

[15] Although hunted for food, this duck was considered to taste bad, rotted quickly, and fetched a low price.

Another possible factor in the bird's extinction was the decline in mussels and other shellfish on which they are believed to have fed in their winter quarters, due to growth of population and industry on the Eastern Seaboard.

[16] Another theory that was said to lead to their extinction was a huge increase of human influence on the coastal ecosystems in North America, causing the birds to flee their niches and find another habitat.

[17][18] These ducks were the only birds whose range was limited to the American coast of the North Atlantic, so changing niches was a difficult task.