Northern Prairie Wildlife Research Center
Based on the application of these criteria, nest success was inadequate to maintain populations in most regions. Exceptions were SDC for all species; NDC (1975-79) for gadwalls, blue-winged teal, and shovelers; and SDE for gadwalls (1980-84) and blue-winged teal (1966-74, 1980-84).
In NDE and NDC, no consistent increase or decrease in nest success was apparent between 1966-74 and 1980-84. In general, nest success was lowest in 1966-74 and highest in 1975-79. Differences among periods were usually <4 percentage points for all species, but ranged from 7 to 10 points for gadwalls, blue-winged teal, and shovelers in NDC. Gadwalls and blue-winged teal had consistently higher nest success rates than pintails and mallards. Rates for shovelers were higher than those for the other species in NDC and SDC but were similar to those for mallards in the other regions.
Nest success varied considerably among the 8 habitat classes in North Dakota (NDE and NDC combined). Success rates consistently approached or exceeded hypothetical threshold levels only in idle grassland and in grassland in 1975-79. Grassland was of major importance to all species studied because it was plentiful and nest success was relatively high. Idle grassland was of minor importance regionally because of its scarcity but may have been important locally because nest success was usually high. Wetland, odd area, and planted cover accounted for about 25% of the nest initiations by all species except pintails. Planted cover was by far the most preferred nesting habitat for all 5 species. Use was highest in 1966-74 because it was more common than in later periods. Because planted cover is highly preferred, it has a great potential for producing ducks if nest success can be increased. Nest success was usually lowest in cropland, hayland, and right-of-way. Use of these 3 habitats was generally low, but pintails initiated >50% of their nests in cropland and mallards and gadwalls initiated between 9 and 13% of their nests in hayland. Losses of grassland, wetland, odd area, and planted cover habitats due to intensive farming practices may cause more ducks to nest in cropland and hayland where nests are exposed to increased risk by predation and farming operations.
Predators were the most important cause of nest losses in all regions and in all habitats. Farming operations caused appreciable losses in cropland and hayland. The most important egg predators common to all regions studied were red fox (Vulpes vulpes), striped skunk (Mephitis mephitis), mink (Mustela vison), raccoon (Procyon lotor), badger (Taxidea taxus), and Franklin's ground squirrel (Spermophilus franklinii) (Sargeant and Arnold 1984). Coyotes (Canis latrans) were present locally, most often in the western parts of NDC and SDC, and reduce red fox predation on female ducks and eggs (Sargeant and Arnold 1984). The same authors thought the red fox had the greatest impact on nest success of upland nesting ducks. Variation in nest success rates among regions was most likely a result of differences in the size and composition of predator populations and differences in the abundance and distribution of their alternative foods.