138 NYROCA VALISINERIA 



Drainage and increased population have greatly reduced the available feeding 

 grounds; even great sheets of water like Tulare Lake have been completely dried up. 



Market statistics for the San Francisco region show that Canvas-backs are much 

 more numerous than Red -heads; possibly some of the latter were passed off on the 

 public under cover of their brethren's more famous name. In the season of 1910-11 

 the American Game Transfer Company received nearly 2000 Canvas-backs out of 

 a total of 71,793 ducks. The Hunters Game Transfer Company marketed 7067 

 "Cans" out of a total of over 357,000 ducks in the five seasons, 1906-11; this was 

 about 2% of the aggregate. In the season of 1910-11 five large transfer companies 

 together handled 8552 Canvas-backs out of a total of 185,900 ducks; in other words, 

 this species comprised about 4.5% of the total number (Grinnell, Bryant and 

 Storer, 1918). 



Nordhoff (1922), in a note written presumably from memory, thinks that shooting 

 clubs at Banning, Riverside County, California, used to take two Canvas-backs for 

 one of any other duck, but memory is a poor guide in matters of this sort. I cannot 

 conceive of such proportions ever having been killed anywhere. 



At the mouth of the Columbia River, Washington, this species is said to occur in 

 "immense flocks" (Kobbe, 1900), and the same is true of parts of the Puget Sound 

 region of Washington. 



In the interior the Canvas-back has been reported as on the increase as a breeder 

 in western Nebraska (Oberholser, 1920). In North Dakota it used to be much more 

 abundant as a nesting bird, but its distribution has been affected by drainage, and it 

 has disappeared in Towner County (Bent, 1901-02). Periods of drought previous to 

 1922 almost ruined this State as a resort for ducks, and these same conditions pre- 

 vailed over a good part of the wheat regions of the West. Still Mr. Mershon (in 

 litt.), who has shot in Kidder County, North Dakota, since 1894, thinks he has 

 noticed a great increase both there and at Buffalo Lake, Alberta. C. B. Horsbrugh 

 (1915), who collected at the latter place, thinks otherwise, and so does Stansell (1909) 

 writing of central Alberta. The truth is that conditions at any one place are always 

 changing, so that minute observation there may not be any criterion of a general 

 increase or decrease. 



Figures compiled by the Minnesota Commissioners show that fewer Canvas- 

 backs than Red-heads are shot in that State. It ranks as the sixth or seventh in 

 order of abundance. 



In the central part of its breeding area, on the Athabasca delta, Harper (MS.) 

 found it the sixth commonest duck. He noted 15 individuals in May, and 126 in 

 June. 



Enemies. The Canvas-back is prey to all the ordinary enemies of the duck tribe, 

 but undoubtedly the Common Crow is the most destructive to the eggs. 



