Northern Prairie Wildlife Research Center
Most recent research in the prairie pothole region on the relationships between the number of duck nests per unit area and hatch rates in established upland cover has been accomplished in stands of introduced grasses and legumes (Duebbert 1969; Duebbert and Kantrud 1974; Duebbert and Lokemoen 1976). It is possible to produce stands of tall, warm-season native grasses with a similar cover form on some soils and sites in the eastern Dakotas and western Minnesota where annual precipitation is 20 inches or more. In these areas, big bluestem (Andropogon gerardi), indiangrass (Sorghastrum nutans), and switchgrass (Panicum virgatum)produce a vegetative form that is similar to cover established from introduced cool-season grasses and legumes. In areas of western North Dakota, eastern Montana, and the southern Canadian provinces, where annual precipitation may be 15 inches or less, it is more difficult to establish tall, dense grassland cover with native grasses. Introduced grasses such as intermediate wheatgrass or tall wheatgrass in a mixture with alfalfa produce stands of tall, dense vegetation in areas such as Medicine Lake National Wildlife Refuge at Medicine Lake, Montana, where the average annual precipitation is 12 inches.
Field size is a factor to consider in establishing seeded cover for duck nesting habitat. No field is too small for grassland establishment, but greater duck nest densities and higher hatch rates have usually been found in relatively large fields (greater than 40 acres) that do not contain wetlands or other habitat divisions. To provide a complete dabbling duck production habitat the fields were surrounded by complexes of Class II, III and IV wetlands (Stewart and Kantrud 1971) adjacent to the field and within a radius of 2 to 3 miles. Adequate wetlands are required to provide habitat for breeding pairs and broods if managed nesting cover is to provide desirable benefits. An example of a good combination of prairie potholes and cover block for dabbling duck production is shown in Fig. 2.
In stands of seeded cover the diameter and strength of the plant stems are important because the vegetation will be resistant to flattening or lodging caused by winter snows. Grasses such as intermediate wheatgrass, tall wheatgrass, bigbluestem, indiangrass, and switchgrass are particularly resistant to flattening. To provide the best cover for nesting ducks in the prairie pothole region, the residual cover in mid-April should be tall enough and dense enough to provide 100% effective screening to a height of 8 inches or more on a cover board or visual obstruction pole when viewed from a distance of 13 feet and a sighting height of 3 feet (Robel et al. 1970).
Grasslands in the prairie pothole region that are managed to provide optimum wildlife habitat should not be subjected to annual grazing or haying to avoid detrimental effects on the essential component of residual vegetation. Seeded grasslands require rejuvenation treatments at intervals of several years and their management should be considered a never-ending activity if cover of optimum quality is to be maintained. Seeded grasslands generally produce more ducks and other game species within the firat 2 to 8 years after establishment or rejuvenation. Rotation systems of cover management should be devised to capitalize on the relationship between young, vigorous stands of vegetation and higher wildlife production.