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Wildlife Monographs

Determinants of Breeding Distributions of Ducks


Breeding Distributions of the Species

American Wigeon.—This species reached high densities in the southern prairie provinces but was often abundant in the north as well (Fig. 6A). Wigeon were uncommon south of Canada. Within prairie and parkland habitats, densities steadily declined away from the area of highest density, much like the mallard and gadwall. Wigeon winter throughout the southern United States, along the Yucatan Peninsula of Mexico, and in the Caribbean. Numbers of spring arrivals using the southern corridors probably slightly outnumber those entering from the southwest (Bellrose 1980). An additional few may migrate to breeding grounds in the parklands directly from wintering locations in the Middle Atlantic States (Bellrose 1980).

gif --American Wigeon Distribution

Figure 6. (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.

Wigeon densities generally did not correlate closely with local pond densities (Table 3). The highest correlations between wigeons and local ponds were in western South Dakota and in the southwestern part of the prairie provinces (Fig. 6B). This pattern is consistent with the large migration of wigeon through the western portal. Higher correlation coefficients between wigeon and ponds were associated with strata with high densities of the species, except that wigeon were common in 3 parkland strata in Alberta and Saskatchewan, but correlations there were low.

Wigeon densities correlated positively with total ponds in many strata of the central portion of its range (Fig. 6C). They were negatively associated in many strata, particularly those on the eastern edge of its range and in the north.

The few appreciable correlations between wigeon numbers and ponds were in the southwestern portion of their range, mostly south of the area of highest densities. When total pond numbers were high, wigeon densities were depressed not only in many strata in the north, but also in several along the eastern edge, suggesting drought displacement both northward and eastward. The limited evidence suggests fairly strong homing by the species (Table 4). We suggest that wigeon arrive on their breeding grounds from the south and the southwest; many remain in strata initially encountered if pond conditions there are satisfactory (thus accounting for the high correlations with ponds there); otherwise they overfly to the north and east.

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