Editing Canvasback (section)

==Diet==
[[File:Tubers.jpg|thumb|Tubers of [[Stuckenia pectinata|Sago Pondweed]] (''Stuckenia pectinata''), a favorite food of the canvasback]]
The canvasback feeds mainly by diving, sometimes dabbling, mostly eating seeds, buds, leaves, tubers, roots, snails, and insect larvae.<ref name=aab/> Besides its namesake, wild celery, the canvasback shows a preference for the tubers of [[Stuckenia pectinata|sago pondweed]], which can make up 100% of its diet at times.<ref>[http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=222000377 Flora of North America: ''Stuckenia pectinata'']</ref> 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.<ref name=dnr>[http://www.dnr.state.md.us/bay/sav/bgic/download/SAV%20It's%20What's%20for%20Dinner.pdf SAV… It’s What’s for Dinner, Developed by Martha Shaum, Aquatic Resources Education Program, Maryland Department of Natural Resources]  {{webarchive|url=https://web.archive.org/web/20110419212353/http://www.dnr.state.md.us/bay/sav/bgic/download/SAV%20It%27s%20What%27s%20for%20Dinner.pdf |date=April 19, 2011 }}</ref> 
[[File:Canvas back duck diving.webm|thumb|Canvasback duck diving]]
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 America]]n 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 [[Macoma balthica|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. [[Redhead (duck)|Redheads]], which also feed on the tubers of sub-aquatic vegetation, have not been able to adapt, and their population remains low.<ref name=dnr/>