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Breeding Distributions of the Species

Canvasback.—The canvasback was most common in the parkland region and in several northern strata (Fig. 12A). Densities declined with distance away from the primary breeding area.

Figure 12. (A) Average species density by stratum, 1955-81; (B) correlation between species density and local pond counts, 1955-81; and (C) correlation between species density and total pond counts, 1955-81.

Correlations with local pond densities had a median of 0.192 (Table 3) and were consistent across much of the surveyed area, including some strata in which canvasbacks were not common (Fig. 12B). In Manitoba, correlations were low, despite high densities of the species. In general, there was no relation between correlation coefficients and average canvasback densities.

Canvasback densities were positively associated with total ponds mostly in central Alberta, southern Saskatchewan, and southwestern Manitoba (Fig. 12C). Correlations were negative in several strata of the north and in central Canada.

Canvasbacks are strongly philopatric (Table 4). To some extent, canvasbacks appear to occupy habitat as it is encountered, although strong homing tends to maintain populations in the primary portion of their breeding range. Displacement is primarily to strata in the north and northwest (Fig. 12C). Dry conditions in the prairie and parkland tended to increase canvasback numbers in the northern and northwestern strata. Hansen (1960) also reported overflight by this species.