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We estimated that agricultural operations, mostly tillage, destroyed 17% of northern pintail nests and 2-3% of those of the other 5 common species. Nests in Cropland usually were dispersed widely, so individual tillage operations seldom destroyed many nests. However, in 1983 we found an unusually high concentration of nests (0.18/ha) in 5 fields of standing stubble on the Hay Lakes and Holden study areas during the first 2 weeks of May. The nests (46 northern pintails, 11 mallards, and 3 northern shovelers) were in 340 ha of wheat that had been cut and swathed the previous autumn, but not harvested because of deep snow; most nests were under swaths and only 5 (8%) hatched. In contrast, we found only 0.01 nest/ha (93 northern pintails, 53 mallards, 12 northern shovelers, 9 blue-winged teals, and 2 gadwalls) in all the remaining stubble fields (15,174 ha) searched during the study; 48 (28%) of these nests hatched.

We estimated that weather events destroyed 1% of nests overall. Snowstorms mainly affected early-nesting mallards and northern pintails when eggs were chilled or nests were abandoned after being buried in deep snow. Among nests known to be present on the Tichfield Study Area in 1982 during the storm of 26-29 May, 14 of 16 (88%) failed because all embryos died or nests were abandoned (10 of 11 mallards and 4 of 5 northern pintails); 8 of the 16 nests were within 4 days of hatching. Among nests known to be present on the Goodwater Study Area in 1983 during the storm of 8-14 May, 16 of 77 (21%) failed as a result of the storm (9 of 43 northern pintails, 6 of 32 mallards, 1 of 1 northern shoveler, and O of 1 American wigeon).

Flooding from heavy rain resulted in abandonment of numerous duck nests located near or in wetlands and drainage ditches on Hay Lakes and Holden study areas in 1983. Among nests known to be present on those study areas during the storms of 18-30 June, 101 of 254 (40%) were abandoned or washed away because of flooding (27 of 61 mallards, 16 of 45 blue-winged teals, 16 of 34 lesser scaups, 19 of 22 ruddy ducks, 8 of 31 northern shovelers, 7 of 21 redheads, 1 of 9 gadwalls, 2 of 7 northern pintails, 1 of 7 canvasbacks, 1 of 5 green-winged teals, 1 of 1 cinnamon teal, and O of 7 American wigeons).

We found 190 nests (all species and area-years pooled) that were abandoned without evidence of egg destruction. We found dead females or their remains at 11% of these nests, but no probable cause for abandonment at the remaining.