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Distribution and Abundance of Predators that Affect
Duck Production: Prairie Pothole Region

Study Areas

The stabilized regulations and Central Flyway study areas are along aerial survey transects used by the Canadian Wildlife Service and the U.S. Fish and Wildlife Service for estimating annual size of breeding waterfowl populations (Bellrose 1976). These study areas are scattered throughout the prairie pothole region (Fig. 1) and represent principal duck nesting habitats. Each study area is 1.6 x 16 km and most areas include an east-west road or trail (center road) that extends lengthwise through the center (Fig. 3). There is no center road in one study area (Morgan) or in 60% of another (Plentywood). Each study area was divided into 40 legal quarter sections. (The legal descriptions of the centers of the west ends of these study areas are provided in Appendix Table 2, and Fig.3 shows reference points.)

The small unit management study areas are located three each in three physiographic regions of western Minnesota (Fergus Falls Till Plain) and eastern North Dakota (Drift Plain, Missouri Coteau). They were selected to represent areas with a potential for high duck production but also represent principal habitats of the respective physiographic regions. Each study area contains nine sections arranged in a north-south by eastwest cross (Fig. 3). (The legal descriptions of the study area centers are provided in Appendix Table 2; Fig. 3 shows reference points.)

Configuration of Study Areas

Figure 3. Configuration of study areas showing the arrangement of quarter section sample units and locations of reference points for legal descriptions (Appendix Table 2).
Twenty-one of the 33 study areas are in the prairie and 12 are in the aspen parkland. Topography is relatively level to moderately rolling in all areas (Fig. 4). The climate of the region is subhumid with cold winters and warm summers. In general, snowmelt occurs during late March and April and is delayed with increases in latitude.

jpg -- Photos of example study areas

Figure 4. Examples of aspen parkland and prairie habitats that comprised the study areas in the prairie pothole region where predator surveys were conducted during 1983-88: (a) aerial view of the Eldridge study area showing central quarter section of federal Waterfowl Production Area, (b) large grassland pasture in the Shamrock study area, 9c) shelterbelts near the Courtenay study area, (d) aerial view of the Lake Park study area, (e) roadside habitat in the Yorkton study area, and (f) aspen parkland-forest habitat in the leask study area.
Most land in each study area is privately owned, but landowners permitted us to work in about 97% of the quarter sections (percentage varied slightly by survey type). Some land in each small unit management study area, including all or part of the center section, is federally owned and managed for waterfowl production (Fig. 4a). Dominant upland habitat types in all study areas are cropland that is cultivated annually and grassland that is grazed by livestock (Table 1). Principal crops are small grains, but include sunflowers in North Dakota and considerable corn and other row crops in Minnesota and South Dakota. Several study areas (Ceylon, Goodwater, Kulm, Shamrock, Yorkton) include portions of large (>10 km2) pastures (Fig. 4b). Other pastures are also present in most study areas, but nearly all are small units (<3 km2). Occupied and abandoned farmsteads are scattered throughout each study area. Undisturbed upland habitats consist primarily of wetland edges, small (<2 ha) areas unsuited for agriculture or neglected during farming and grazing, abandoned farmsteads, wildlife management tracts (in some study areas in the United States), and some wooded areas.

Trees are scattered throughout each study area, but are most numerous in study areas in the aspen parkland (Table 1). Most trees in study areas in the prairie are in single-row shelterbelts in fields (Fig. 4c) and in multi-row windbreaks at farmsteads. In the aspen parkland, quaking aspen trees with hazelnut (Corylus sp.) or willow understory are prevalent around wetlands and in small woodlots. Oak trees (Quercus spp.) are common in woodlots in the three study areas in Minnesota. Woodlots of up to 0.65 km2 are present in six study areas (Hay Lakes, Hawley, Hitterdal, Holden, Leask, Yorkton). Additional data on physiography, habitats, and land-use in the prairie pothole region are provided by Bird (1961), Coupland (1961), Kiel et al. (1972), Stewart and Kantrud (1972), Brewster et al. (1976), and Cowardin et al. (1985).

Mammalian predators were removed annually from April through June on federal land in the center of three small unit management study areas (Eldridge, Fredonia, Lake Park). The removal was part of an evaluation of effects of localized removal of predators on nest success in ducks. No other known organized removal of predators with probable influence on our findings occurred. However, furbearers were trapped in all study areas, and in five study areas (Ceylon, Hanley, Litchville, Shamrock, Penhold), we found evidence of indiscriminate killing of predators.

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