Hobbies And Interests
Canvasback Facts
Canvasbacks are among the largest diving ducks. The male, with the white back that probably gave the species its common name, averages about 21 inches in length and weighs about 2.7 pounds, while the female is slightly smaller. In the late-19th and early-20th centuries, this duck was considered a treat in East Coast restaurants, and commercial hunting severely threatened the population until the Migratory Bird Treaty Act of 1918 allowed the government to set bag limits. A United States Fish and Wildlife Service survey in 2009 estimated the current population at about 662,000.
Summer Nesting Habitat
The canvasback spends summers on the prairies of Minnesota, North and South Dakota and the Canadian provinces of Manitoba, Saskatchewan and Alberta. It nests in depressions filled with water, or potholes, left by melting Ice Age glaciers. These wetlands provide materials for nests and hiding areas in clumps of cattails, bulrushes or wild grasses. There is also abundant food in the seeds, roots and tubers of aquatic plants, as well as snails and insect larvae. The hen lays a clutch of eight to 10 eggs, which incubate for 25 days, and raises the ducklings alone.
Dangers on the Prairies
The canvasback duck is also threatened by alterations in its summer nesting grounds. As agricultural use of the land increases, potholes are drained or filled in to provide more acreage for crops. When this occurs, there are fewer nesting sites, as well as less food for the duck population. Other threats to the canvasback in this region include predators, such as foxes and raccoons, and extreme weather conditions, particularly prolonged droughts.
Winter Quarters
In the fall, canvasbacks migrate south along the Atlantic, Mississippi and Pacific flyways to wintering areas on the Atlantic coast, the lower Mississippi River and the California coast. These locations provide the submerged aquatic vegetation the canvasback duck prefers, along with small clams and snails. Historically, about half of the species' population wintered on the Chesapeake Bay where a favorite food, wild celery, grew in abundance. The canvasback's connection to wild celery, or Vallisneria Americana, was so strong, it gave the duck its scientific name of Aythya valisineria.
Chesapeake Bay Habitat Threats
Conditions in the Chesapeake region, where declining water quality limits the growth of submerged aquatic vegetation, including wild celery, now push large numbers of birds to other wintering regions. Silt carried into the water from construction projects and shoreline erosion prevents sunlight from reaching underwater plants, and clouds of algae that thrive on nutrients discharged by sewage treatment facilities also block the sun. In addition, runoff from areas adjacent to the Bay may contain toxins, such as pesticides and herbicides.