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Aythya valisineria
– Family
Authors: Mowbray, Thomas B.

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Adult male Canvasback, breeding plumage.
Figure 1. Distribution of the Canvasback.

This exclusively North American species is considered the “aristocrat of ducks.” The male’s striking appearance—rich chestnut-red head and neck, black chest, white back, and long, sloping, blackish bill—along with its large size distinguish it in the field. The Canvasback’s center of breeding is in the prairie-parklands of southern Canada, with major concentrations in winter along the Atlantic Coast (Chesapeake Bay and Pamlico Sound, North Carolina), Mississippi River delta and delta lakes in southern Louisiana, and San Francisco and San Pablo Bays, California. The species takes its specific name, Aythya valisineria, from Vallisneria americana, or wild celery, whose winter buds and rhizomes are its preferred food during the nonbreeding period. This is an omnivorous duck but specialized in its trophic requirements, preferring winter buds, tubers, rhizomes, and root stalks of submergent plants, as well as benthic invertebrates. Although often found in shallow water, the Canvasback is an adroit diver, diving to depths of more than 9 meters.

Gregarious and highly visible during the nonbreeding season, the Canvasback is monogamous and secretive during the breeding season. Pairs form during spring migration and continue to do so until they reach the breeding grounds. The breeding home range is large for this species, encompassing several ponds that pairs use for nesting, feeding, loafing, and brooding. The Canvasback nests over water, in a large structure constructed of loosely woven reeds and sedges and lined with down. This species is an ecological specialist whose restricted nesting and specific trophic requirements link it inextricably to deeper, more stable ponds, marshes, and potholes. During periods of severe drought, it responds promptly by delaying breeding or failing to breed at all, accounting in part for its small population size; this is one of the least abundant species of ducks in North America. The Canvasback is a primary host for parasitic egg-laying by the Redhead (A. americana), and brood parasitism is an important factor affecting its nesting success.

Since the 1960s, Canvasbacks have altered their traditional migration routes, changed wintering sites, and modified diets in response to changes in the availability and predictability of certain foods, changes generally attributed to declining abundance of plant tubers. Today, the species migrates along 3 principal corridors, with yearly local abundance varying considerably, depending on availability of food, weather conditions, disturbances, and hunting pressures. As a result of extensive molt-migration of males, sexes and age classes segregate during fall migration, causing highly disparate sex ratios at staging, stopover, and wintering areas; mixing of males and females during the nonbreeding season occurs primarily on the wintering grounds and spring migration.

The Canvasback is one of the most studied species of duck in North America. Excellent long-term studies of breeding populations at Minnedosa, Manitoba, have given us a unique synthesis of the overall biology of the species. Studies on the breeding grounds have contributed to our understanding of pair-bond and social behavior during the breeding cycle (Anderson 1984, 1985a); factors affecting reproductive success (Stoudt 1982, Barzen and Serie 1990, Serie et al. 1992, Arnold et al. 1995, Anderson et al. 1997); probability of recruitment of juvenile females into the breeding population (Anderson et al. 1997, 2001); habitat use, survival, and movements of ducklings (Austin and Serie 1991, 1994; Leonard et al. 1996); and the behavioral response of Canvasbacks to brood parasitism by Redheads (Sorenson 1993, 1997; Sayler 1996). Studies at staging areas, at migratory-stopover sites, and on the wintering grounds have clarified timing and routes of migration (Serie et al. 1983, Reinecker 1985), food habits (Noyes and Jarvis 1985; Jarvis and Noyes 1986; Perry and Uhler 1988; Serie and Sharp 1989; Austin et al. 1990; Hohman et al. 1990a; Jorde et al. 1995; Thompson and Drobney 1996, 1997; Haramis et al. 2001), factors affecting winter and annual survival (Haramis et al. 1986, 1993; Hohman 1993; Hohman et al. 1993, 1995; Lovvorn 1994), social behavior (Alexander 1987; Takekawa 1987; Lovvorn 1989b, 1990; Hohman and Rave 1990; Howerter 1990; Thompson 1992; Bielefeld 1993), and foraging ecology (Takekawa 1987, Tome and Wrubleski 1988, Lovvorn and Jones 1991, Lovvorn et al. 1991, Ball 1994).