CANVAS-BACK 133 



Canvas-backs arrive on their breeding grounds no later than the mass of surface- 

 feeders, but the nesting period is not particularly early. Evidently they do not pair 

 up until late March or early April and the last ten days of May and the first half of 

 June constitute the usual laying period. Nests were found as early as May 18 in 

 North Dakota (Job, 1899). Another early date is May 21 for British Columbia 

 (A. Brooks, fide J. and J. M. Macoun, 1909). At Barr Lake, Colorado, full comple- 

 ments were found on June 15 (Rockwell, 1911). Most of the other dates vary from 

 late May to mid-June for North Dakota, Saskatchewan, and Alberta. Farther north, 

 Harper (MS.) found several nests on the lower Athabasca between June 18 and 21. 

 Later clutches are, of course, common in all these regions, and nests are found up to 

 July 1. Some of these are second clutches after the first have been destroyed. 



The nest site is the same as that of the Red-head and the Ruddy Duck. Thick 

 beds of dead reeds, bulrushes or tules standing in shallow water or mud are the lo- 

 calities usually chosen. Like other diving ducks, the Canvas-back seeks inaccessible 

 places such as islands and impenetrable bogs. At Prince Albert, Saskatchewan, a 

 nest was found placed in the base of a willow-bush standing in water; another was in 

 a tussock of dead grass in a small slough (Ferry, 1910). Both in southern Saskatche- 

 wan and in Colorado nests were found placed in burrows dug into the top of muskrat 

 houses (Spreadborough, in J. and J. M. Macoun, 1909; Rockwell, 1911). Usually 

 nests are well concealed, but sometimes they are located in rather conspicuous posi- 

 tions among open scattered rushes. 



The nest itself is a bulky structure, ordinarily made of dead flags or sedge, eight or 

 twelve inches above the water, and sometimes with an inclined runway leading to 

 the top of one side, which the female seems to use in going to and coming away from 

 the nest. The outside diameter of the nest is about fourteen inches, and the inside 

 about seven to eight inches (Bent, 1901-02). 



The interior is usually well supplied with down of a gray color, which is easily dis- 

 tinguished from that of other species, especially that of the Red-head, by its darker 

 color (A. Brooks, 1903; Bent, 1901-02; Wolfe, in litt.). The normal clutch varies 

 from seven to ten, the average being perhaps eight or nine. The largest clutch I find 

 recorded was taken in Colorado and contained fourteen eggs (Rockwell, 1911) and 

 sets up to twelve are not unusual. Job (1902) places the average at ten or eleven, but 

 adds that at times he only found seven. So many other nests have been found with 

 only seven eggs that I think Job's estimate may be somewhat too high. 



Both the Red-head and the Ruddy Duck utilize the Canvas-back as a foster 

 mother, but all observers are unanimous in saying that the Canvas-back attends 

 strictly to its own business and does not invade the sanctity of its neighbors' 

 homes. 



The eggs are rich grayish olive to greenish drab in color and measure from 59.9- 

 65.3 mm. in length and from 42.6-45.7 mm. in breadth. The average is 62.8 by 



