Кенепқұйрық үйрек туралы ақпарат

Species of bird

The canvasback (Aythya valisineria) is a species of diving duck, the largest found in North America.

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. 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.

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.

The canvasback feeds mainly by diving, sometimes dabbling, mostly eating seeds, buds, leaves, tubers, roots, snails, and insect larvae. The canvasback has large webbed feet adapted for diving and its bill helps it dig tubers from the substrate. In the late 1930s, studies showed that four fifths of the food eaten by canvasbacks was plant material. In the early 1950s it was estimated that there were 225,000 canvasbacks wintering in the Chesapeake Bay; this represented one half of the entire North American population. By 1985, there were only 50,000 ducks wintering there, or one tenth of the population. Canvasbacks were extensively hunted around the start of the 20th century, but federal hunting regulations now restrict their harvest, so hunting is ruled out as a cause for the decline. Scientists have now concluded that the decline in duck populations was due to the decline in sub aquatic vegetation acreage. Today the population has stabilized and is even increasing slightly, although it is nowhere near previous levels. Studies have now shown that by the 1970s four fifths of the ducks' diet was made up of Baltic Clams, which are very common in the Chesapeake Bay: the ducks have been able to adapt to the decline in sub aquatic vegetation by changing their diet. Redheads, which also feed on the tubers of sub aquatic vegetation, have not been able to adapt, and their population remains low. Edith Wharton refers to canvasback with blackcurrant sauce as an especially luxurious dinner served in New York City in the 1870s. Canvasback duck was a canonical element, along with Terrapin à la Maryland, of the elegant "Maryland Feast" menu, an "elite standard that lasted for decades".

Populations have fluctuated widely. Low levels in the 1980s put the canvasback on lists of special concern, but numbers increased greatly in the 1990s. The canvasback is particularly vulnerable to drought and wetland drainage on the prairies of North America. Many species of ducks, including the canvasback, are highly migratory, but are effectively conserved by protecting the places where they nest, even though they may be hunted away from their breeding grounds. Protecting key feeding and breeding grounds is key for conserving many types of migratory birds.