The canvasback (Aythya valisineria) is a species of diving duck, the largest found in North America. Taxonomy Scottish-American naturalist Alexander Wilson described the canvasback in 1814. The genus name is derived from Greek aithuia, an unidentified seabird mentioned by authors, including Hesychius and Aristotle. The species name valisineria comes from the wild celery Vallisneria americana, whose winter buds and rhizomes are the canvasback's preferred food during the nonbreeding period. The celery genus is itself named for seventeenth century Italian botanist Antonio Vallisneri. The duck's common name is based on early European inhabitants of North America's assertion that its back was a canvas-like color. In other languages it is just a white-backed duck; for example in French, morillon à dos blanc, or Spanish, pato lomo blanco. In Mexico it is called pato coacoxtle. Description It ranges from in length and weighs , with a wingspan of . It is the largest species in the genus Aythya, being similar in size to a mallard but with a heavier and more compact build than it. 191 males wintering in western New York averaged and 54 females there averaged . The canvasback has a distinctive wedge-shaped head and long graceful neck. The adult male (drake) has a black bill, a chestnut red head and neck, a black breast, a grayish back, black rump, and a blackish brown tail. The drake's sides, back, and belly are white with fine vermiculation resembling the weave of a canvas, which gave rise to the bird's common name. The bill is blackish and the legs and feet are bluish-gray. The iris is bright red in the spring, but duller in the winter. The adult female (hen) also has a black bill, a light brown head and neck, grading into a darker brown chest and foreback. The sides, flanks, and back are grayish brown. The bill is blackish and the legs and feet are bluish-gray. Its sloping profile distinguishes it from other ducks. Breeding The breeding habitat of the canvasback is in North American prairie potholes. The bulky nest is built from vegetation in a marsh and lined with down. Loss of nesting habitat has caused populations to decline. The canvasback usually takes a new mate each year, pairing in late winter on ocean bays. It prefers to nest over water on permanent prairie marshes surrounded by emergent vegetation, such as cattails and bulrushes, which provide protective cover. Other important