Canvasbacks are sometimes called the "aristocrat of ducks" for their elegant appearance. Canvasbacks are the largest diving duck (Aythya) species. Males are slightly larger, from 51 to 56 cm in body length and 863 to 1,589 g mass. Females are from 48 to 52 cm in body length and 908 to 1,543 g in mass. Canvasbacks are distinguished by their large size and characteristic long, sloping profile and wedge-shaped head that is held erect on their long necks. Canvasback breeding plumage, which they keep for most of the year, is striking. Males have rich, reddish-brown heads and necks, black breasts, and white wings, sides, and belly. The rump and tail feathers are black. The feet and legs are dark grey and the bill is black. Female breeding plumage is much more subdued, but similar to males; the head and neck are brownish, the wings, sides, and belly are white or gray, and the tail and breast are dark brown. Non-breeding males and females, and immature individuals, are generally brownish overall. Canvasbacks are sometimes confused with their close relatives: redheads, greater scaup and lesser scaup. (Mowbray, 2002)
Canvasbacks breed in the prairie pothole region of central North America, from Colorado and Nevada north through Canada to central Alaska. Breeding populations seems to be moving farther northward in recent years. The winter range is from Pacific coast across the central prairie states to the southern Great Lakes and south to Florida, Mexico, and Baja California. The largest winter concentrations of canvasbacks are found in Lake St. Clair, the Detroit River and eastern Lake Erie, Puget Sound, San Francisco Bay, the Mississippi River delta, the Chesapeake Bay and Currituck and Pamlico sounds in North Carolina.
In the breeding season canvasbacks are found in areas with small ponds, slow moving rivers, and dense vegetation. Most breeding occurs in areas of central Canada characterized by aspen woodlands, grasslands, and potholes. Canvasbacks prefer breeding in small lakes and ponds or marshes with dense emergent vegetation, such as cattails and reeds. During spring and fall migration and winter canvasbacks are found in aquatic areas with high densities of food availability, including estuaries, large freshwater lakes, coastal bays and harbors, and large river deltas. During migration they may also use flooded fields, farm ponds, and wetlands.
Canvasbacks usually have a single mate each breeding season, although they may have a different mate in each breeding season. Courtship begins during the spring migration and continues on the breeding grounds. During the height of courtship, females may be surrounded by 3 to 8 males in "courting parties." Females choose their mate from these groups. There are a variety of courtship displays used between mates: the neck-stretch, incite behavior, a male sneak approach, kinked-neck, head-throw, and turning the back of the head.
Females choose the same home ranges for their nesting sites each year. Nests are started as early as late April, but nesting peaks in mid to late May and may continue into June. Pairs lay one brood per year, although they will re-nest if the first brood is destroyed. Nests are built in emergent vegetation above water, although they will occasionally build nests on land as long as it is in a protected area. They prefer medium to large sized, shallow wetlands with extensive emergent vegetation for breeding. Females lay from 5 to 11 smooth, elliptical, greenish drab eggs. Average reported clutch sizes vary regionally, but range from 6.6 to 8.3 eggs per nest. Clutch sizes may be affected by nest parasitism, with parasitized nests having smaller clutches. One egg is laid per day and the female begins to incubate the eggs a few days before the last egg is laid. Eggs are incubated for 24 to 29 days. Young are able to swim and forage soon after hatching. Young fledge at 56 to 68 days after hatching. In late August or September young canvasbacks form groups in preparation for migration. Canvasbacks are capable of breeding in the year after hatching.
Females build nests and line them with plants and down feathers. Male canvasbacks are protective of their mate and the nest for the first few weeks that the eggs are being incubated. After that, they abandon the females and their nests. Young canvasbacks can swim and feed themselves as soon as their feathers dry after they hatch, although their mother will protect them against cold weather. Within a day after hatching the female and her brood abandon the nest and move into larger lakes and ponds with lots of vegetation. Females remain with their broods until close to migration in the fall. For broods that hatch late in the year, though, that may be at only 2 to 3 weeks old.
The oldest wild canvasback captured was 22 years and 7 months old, the next longest recorded lifespan in a wild canvasback was 16 years 11 months.
Canvasbacks are active during the day, they are highly social, and they migrate seasonally between breeding and non-breeding ranges. They migrate in loose V-shaped flocks and are one of the fastest flying ducks. They can fly up to 90 km/hour air speed (115 km/hour ground speed). They have to run along the water for some distance before they can take flight. Canvasbacks are efficient and powerful swimmers, with their legs positioned near the rear of their body. They may spend up to 20% of the day swimming and can dive to over 9 meters deep for 10 to 20 seconds.
Canvasbacks maintain home ranges during the breeding season that vary in size. In one study, home ranges were about 73 hectares before nesting, increased to about 150 hectares before laying the eggs, and then declined to about 25 hectares when the eggs were laid. (Mowbray, 2002)
Canvasbacks are generally quiet ducks, although they do use a variety of distress calls and emit a variety of coos and rattles as part of courtship behaviors. They use visual signals in courtship, through their displays. (Mowbray, 2002)
Canvasbacks are omnivorous, eating both plants and animals as they are available. In winter and migration they mainly eat aquatic plants, especially the underwater roots. They may also take small snails and clams during this time. In the breeding season canvasbacks eat aquatic plants and animals, including the seeds, buds, leaves, and roots of aquatic plants and snails, caddisfly larvae, dragonfly nymphs, mayfly nymphs, and midge larvae. Canvasbacks forage in small to very large groups (over 1000) and mainly in the morning and evening. They can dive to more than 5 meters deep for 10 to 20 seconds. They take food in a variety of ways, including diving, stripping plants with their feet or beaks, and grabbing prey from the water surface or air. In a dive they use their strong, cone-shaped heads to probe and pull-up submerged plants.
The scientific name of canvasbacks comes from their favorite winter food, the aquatic plant Vallisneria americana, or wild celery. (Mowbray, 2002)
Canvasback eggs and young are preyed on by a variety of nest predators, including raccoons, striped skunks, red foxes, mink, ermine, American crows, black-billed magpies, common ravens, and California gulls. Adults and fledglings are preyed on by raptors as well as large terrestrial and aquatic predators, including: mink, coyotes, great black-backed gulls, bald eagles, great horned owls, black-crowned night herons, snapping turtles, and northern pike. (Mowbray, 2002)
When a female notices a predator near her nest, she silently swims away to distract attention. If the young are hatched, the female uses a warning call so that the young swim into thick vegetation. Outside of the breeding season canvasbacks form large groups to help protect against predation. Predation accounts for up to 60% of duckling mortality. (Mowbray, 2002)
Canvasbacks form large groups in the non-breeding season, which can have a substantial effect on local aquatic ecosystems. Canvasbacks are infected by a variety of diseases and parasites
Other canvasbacks and two other duck species will lay their eggs in canvasback nests, a form of parasitism called "nest-parasitism." The most important nest parasites of canvasbacks are their close relatives redheads, they are also parasitized by ruddy ducks. Canvasback nests with redhead eggs in them are more likely to have the canvasback eggs damaged, be abandoned by the parents, and the ducklings are less likely to survive.
There are no adverse effects of canvasbacks on humans.
Canvasbacks are important members of healthy, aquatic ecosystems. They are also an important game species and are one of the best studied duck species. (Mowbray, 2002)
Canvasbacks are protected as migratory gamebirds in the United States, Mexico, and Canada. They are not considered threatened or endangered currently. Populations are affected by hunting pressure, habitat degradation, pollution, and collisions with cars or stationary objects. Hunting pressure is most intense during fall migration. In 1999 approximately 87,000 canvasbacks were taken by U.S. hunters. Because canvasbacks eat vegetation in aquatic sediments, they are susceptible to the toxins that accumulate in those sediments. This is especially true in areas of high industrial activity, such as the Detroit River.
Tanya Dewey (author), Animal Diversity Web.
Mowbray, T. 2002. Canvasbacks, Aythya valisineria. The Birds of North America Online, 659: 1-20. Accessed December 05, 2008 at http://bna.birds.cornell.edu/bna/species/659.