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Breeding Distributions of these Species

General Patterns.—These 10 species have highest densities mostly in the prairie and parkland of southern Canada. Gadwall and blue-winged teal had distributions centered somewhat more to the south; American wigeon, green-winged teal, pintail, and scaup had more northern ones; and the canvasback was centered northward and eastward. During migration, nearly all gadwalls, blue-winged teal, redheads, and scaup enter their primary breeding ranges from the south. These corridors are taken by about 75% of green-winged teal, mallards, and canvasbacks, and by about 60% of American wigeons and northern shovelers. Only about 40% of returning northern pintails use the southern corridor.

Overall, species densities tended to correlate positively with pond densities in the same transect. This relation was strongest among pintails, but also pronounced in mallards, blue-winged teal, and shovelers.

Three species, American wigeon, northern shoveler, and northern pintail, tended to have higher correlations with ponds in those strata where each species was most abundant. These species also were the ones that made less use of the southern portal to the breeding range.

Pintail densities were more closely related to total ponds than the other species, with strong positive correlations in the southern prairie provinces and in the north central states, and negative correlations in the northern strata. The shoveler and mallard exhibited similar, but slightly weaker, relations. Several species—gadwall, wigeon, blue-winged teal, redhead, and lesser scaup—displayed negative correlations in 1 or more strata in the southern part of their primary range, suggesting that these strata may be the destination of Drought displaced birds.

Homing rates were highest for the redhead, canvasback, and lesser scaup, moderately high for the mallard, gadwall, American wigeon, and northern shoveler; and lowest for the blue-winged teal. Little is known about homing by the pintail, and no information is available for the green-winged teal.