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Temperature, precipitation, and availability of wet seasonal wetlands in May were correlated with median nest-initiation dates of mallards (R² = 0.28, n = 30, P = 0.01), blue-winged teals (R² = 0.26, n = 21, P = 0.11), and northern pintails (R² = 0.23, n = 21, P = 0.03). Median nest-initiation date decreased by 2.3 days for mallards (P = 0.01) and by 1.2 days for blue-winged teals (P = 0.09) per Celsius degree increase in average May temperature. Median nest-initiation date of blue-winged teals was positively related to amount of precipitation in May (P = 0.08). Median nest-initiation dates of mallards (P = 0.08) and northern pintails (P = 0.03) were positively related to number of wet wetlands present in May.

Average length of nest-initiation period (measured by interquartile range) did not differ (P > 0.05) between mallards (27 days) and northern pintails (26 days), or among gadwalls (13 days), blue-winged teals (15 days), and northern shovelers (16 days) (Fig. 2). Nest-initiation periods of the latter 3 species were shorter than those of mallards and northern pintails (P < 0.05).

Availability of wet wetlands in May, April-June temperature and precipitation, and nest success were correlated with length of nest-initiation period (mallards, R² = 0.16, n = 30, P = 0.09; gadwalls, R² = 0.23, n = 15, P = 0.07; blue-winged teals, R² = 0.33, n = 21, P = 0.03; northern shovelers, R² = 0.44, n = 17, P < 0.01; and northern pintails R² = 0.29, n = 21, P = 0.09). Nest-initiation period decreased by 0.29 day (P = 0.11) for mallards and by 0.52 day (P = 0.08) for northern pintails for every 1 percentage point increase in nest success. Nest-initiation period was extended by 0.10 day for mallards (P = 0.04) and by 0.12 day for northern pintails (P = 0.03) per 1.0 cm increase in May precipitation.

The nest-initiation period was extended by 0.10 day for gadwalls for every 1 percentage point increase in number of wet wetlands present in May (P = 0.07). The nest-initiation period of blue-winged teals was extended by 0.06 day per 1.0 cm increase in May precipitation (P = 0.11) and decreased by 1.4 days per Celsius degree increase in June temperature (P = 0.04). The nest-initiation period of northern shovelers was extended by 0.13 day for every 1.0 cm increase in April precipitation (P < 0.01).

Fig. 2. Minimums and maximums, medians, and interquartiles of estimated nest-initiation dates for 5 common species of dabbling ducks in the Prairie Pothole Region of Canada. Number of study areas is in parentheses.