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Wildlife Monographs

Determinants of Breeding Distributions of Ducks


Breeding Distributions of the Species

Northern Shoveler.—Shovelers reached highest densities mostly in the prairie and parkland strata of the southern prairie provinces and central North Dakota (Fig. 9A). Average densities tended to decline away from the primary breeding area.

gif --Northern Shoveler Distribution

Figure 9. (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.

Shovelers winter mostly in California the west coast of Mexico, and the Gulf Coast of Texas and Louisiana (Bellrose 1980). Nearly 60% of them probably return in spring through the southern portal, and most of the rest enter through the western portal.

Densities of this species varied markedly in response to local pond numbers (Table 3). Correlations were greatest where shovelers were common, except in strata along the northeastern edge of the primary area where shovelers were common but did not correlate highly with ponds (Fig. 9B).

There was a clear distinction between the southern part of the shoveler's range, where it tended to correlate positively with total ponds, and the northern portion, where the reverse held (Fig.9C). Drought displaced birds seem to settle northwest, north, and northeast of the primary area.

Although shovelers home at a fairly high rate (Table 4), they respond positively to pond conditions, particularly in the southern and western part of the surveyed area. The pattern of correlations is consistent with the idea that there are 2 pathways into the breeding range, one from the south, the other from the west. Birds arriving from either direction may settle in the southern or western strata, if ponds there are adequate; otherwise, they move on to the northwest, north, or northeast.

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