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Factors Associated with Duck Nest Success
in the Prairie Pothole Region of Canada

Conclusions

  1. On most of our study areas in the PPR of Canada during 1982-85, native habitats used by ducks for nesting were extensively reduced in amount and fragmented because of prior clearing and cultivation.

  2. Annual estimates of nest success were at or above suggested threshold levels for maintaining stable populations (15%) for mallards and northern pintails in 8 of 31 area-years and (20%) for gadwalls, blue-winged teals, and northern shovelers in 4 of 31 area-years.

  3. Approximately 77% of all nests initiated failed directly because of predation. Although predation was the overwhelming cause of nest failure, predator numbers did not appear to be the sole determinants of predation. Predation rates were related to weather variables and other factors that may have strongly affected nest success (possibly abundance of buffer prey and extent of fragmentation of nesting habitat).

  4. Large pastures in native grassland were probably the most productive areas for upland-nesting ducks. Productivity was related to size of pasture, amount of brush, and mammalian predator community. Large pastures were remote and had few roads and infrequent visitors—all factors that probably contributed to habitation by coyotes.

  5. Nest success was negatively correlated with amount of cropland present and decreased about 4 percentage points for every 10 percentage points increase in amount of cropland. Under conditions of our study in the prairie physiographic zone, we predict that the 5 common species cannot maintain local breeding populations where cropland exceeds about 56% of the habitat.

  6. In areas where cropland is abundant, nesting habitat usually is in fragmented tracts that tend to be occupied by a mammalian predator community dominated by red foxes.

  7. Warm weather, precipitation, and abundant wet wetlands in April and May promoted early nest initiation. Length of nest-initiation period was extended by precipitation during the nesting season, but high rates of nest success and above average temperatures tended to shorten it.

  8. Ducks initiating nests toward the end of the breeding season tended to suffer lower rates of nest predation than earlier nesters, which imparted an advantage to renesting ducks and late-nesting species.

  9. Relatively high mortality of ducks, especially females, occurred during the breeding season due to predation, most likely by red foxes, coyotes, northern harriers, Swainson's hawks, red-tailed hawks, and great horned owls. Mallards and northern pintails were especially abundant among dead ducks because they nested early when other prey likely were scant. Females were more vulnerable to predators during the breeding season than were males because females tended the nest. Many abandoned nests, at which we found no evidence of egg destruction, were probably due to death of the female.

  10. Nest success rate, as indexed by the number of successful nests, appeared to be the most influential factor in determining mallard production. Size of the breeding population also was strongly influential.

  11. Nest success varied geographically, annually, and in response to other unidentified factors. Components of variance associated with unexplained variation exceeded those associated with either geographic or temporal variation for all variables, except for number and extent of temporary wetlands.

  12. Large areas of the PPR in Canada presently are not producing the sustainable populations of dabbling ducks for which this Region was known in past decades. Although we believe our study areas represent habitat conditions across the PPR of Canada, it is possible conditions on our study areas were better for duck production than other parts of the Region. If our study areas represent the best areas for duck production, then much of this important breeding ground probably is less suitable for nesting ducks than we observed.
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