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Breeding Distributions of the Species

Redhead.—This diving duck had highest densities in the parkland of the prairie provinces, the mixed forest of southern Saskatchewan, and the central Dakotas (Fig.11A). Average densities tended to decline steadily with distance from these areas.

Figure 11. (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 between densities of this species and local ponds were mostly low (Table 3), including strata with highest redhead densities (Fig. 11B).

Redheads responded positively to total ponds in only a few strata in the southern prairie provinces and in south-central North Dakota (Fig. 11C). Negative correlations were calculated for several strata in the northern part of its range and in east-central Montana. In spite of low correlations with local wetland counts, redheads were less common in these strata when total pond numbers were high.

Redheads appear to be strongly philopatric (Table 4), which may also contribute to the weakness of the relation between local pond counts and numbers of redheads. Hochbaum (1946) suggested that the redhead, as a diving duck, was a poor pioneer. McKnight (1974) disagreed, citing a rapid buildup of redheads in newly impounded marshland in Utah.

Redhead densities did not relate closely to local pond counts, possibly because they prefer the more stable semipermanent wetlands, which fluctuate less in numbers than do temporary and seasonal ponds. Moreover, the strength of associations with pond numbers did not display a latitudinal gradient (Fig. 11B). Thus, some redheads seem to respond to pond conditions encountered on their northward flight, but most migrate to their primary range. If wetland conditions there are not suitable they continue northward (see Hansen 1960) or retreat into Montana.