Northern Prairie Wildlife Research Center
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.)
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).
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.
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.