Northern Prairie Wildlife Research Center
The substantial increase in prairie chicken numbers on the SNG between 1961 and 1987 was almost entirely attributed to changes in land management, primarily grazing practices (Kobriger et al. 1988). When the Sheyenne grasslands were managed with season-long grazing, the prairie chicken population was apparently kept at the threshold of extinction (greater than or equal to; 10 males in total per year). Season-long grazing, which occurs on a few allotments of the SNG, had visual obstruction readings (VOR) below the minimum determined necessary (1.5 dm) to provide adequate prairie grouse concealment cover for nesting or roosting (Manske et al. 1988). Manske et al. (1988) reported 79% of 14 prairie grouse nests found at the SNG were located in pastures that had been grazed for 2 or 3 periods the previous year. Management treatments with the pastures grazed for 2 periods showed benefit to grassland vegetation, prairie grouse habitat and populations. They concluded that prairie grouse select for pastures with 2 or 3 grazing periods for display ground and nest locations. Some have cautioned against using these data to draw hard conclusions, however, due to a small sample of nests (Jensen 1992).
Newell et al. (1988a) found the majority of SNG prairie grouse nests on public land were in 3-pasture deferred systems. The deferred pasture of 3-pasture systems was used by brood and non-brood hens a high percentage of the time relative to other pastures. Nest success in pastures grazed season-long had a very low success (1 in 7). Most nests were in what they described as the lowland community. However, there may be some confusion between what Newell et al. (1988a) called a lowland community relative to what Manske (1980) considered lowland. Barker (personal commun.) suggested that the community considered by Newell et al. as lowland was very likely what NDSU researchers have termed the midland habitat type of the Deltaic Plains Habitat Association. In any case, successful nests had greater densities of vegetation at 0, 5 and 10 m from the nest than unsuccessful nests (Newell et al. 1988). Both brood and non-brood hens selected areas that had not been disturbed by grazing during the current year. Eng et al. (1988) found renests on the SNG were more successful than initial nests and believed this was due to a lack of residual cover for early nests. Jensen (1992) concluded that prairie chickens must select nest sites from diminished residual cover as a result of current grazing practices. Much of the residual cover which is available is confined to lowlands which are susceptible to flooding in some years. Nesting also occurs in the narrow midland habitat at the back and foot of the slopes in the hummocky sandhills association which is somewhat susceptible to mammalian predators.
Jensen (1992) reported on studies in North and South Dakota which evaluated grazing systems relative to providing adequate residual cover for prairie chickens. Three of the 7 studies recommended a rest or deferred rotation (Kohn 1976, Rice and Carter 1982, Newell et al. 1988a). Two recommended twice-over rotations (Manske et al. 1988, Sedivec and Barker 1989). One study did recommend a season-long system (Mattise 1978) although it considered only sharp-tailed grouse. One study was inconclusive (Grosz 1982). Kobriger et al. (1988) mentioned circumstantial evidence that declining prairie chicken populations were correlated with the initiation of rapid rotation systems which began in the early 1980's. Given Newell's (1988a) assessment of chickens avoiding areas with cattle, rapid rotation systems have the potential to cause more brood movements, which would likely lead to greater predation. Jensen (1992) stated that evidence appears to support a 3-pasture, once-over, deferred system as being superior in providing cover. One over-riding theme of all these studies was the value to prairie grouse of more residual cover.
Grazing and South Dakota prairie grouse
Rice and Carter (1982) found that height and density of forage left ungrazed was influenced by both the grazing system and stocking rate of individual allotments. When all range sites were combined, forage left ungrazed in a rest rotation system was significantly higher than forage in deferred rotation systems due to forage present in the ungrazed rest rotation pastures. Although the acres/AUM for the entire rest rotation grazing system were the lowest for any grazing system tested, this system still left more forage ungrazed than the deferred rotation system. Comparisons between systems showed winter pastures produced 10.14 nests and broods/1,000 acres searched. Ungrazed rest rotation pastures were next highest at 9.27 nests and broods/1,000 acres. Fewest nests-broods were found on deferred rotation systems (0.84/1,000 acres). Rest rotation grazing systems were substantially more beneficial to grouse nesting and brooding than deferred rotation. Vegetative differences between rest and deferred rotation were due to grazing system design rather than AUM usage. Even when nest counts from the grazed pastures of the rest rotation system were included in the analysis, there were still significantly more grouse nests and broods/1,000 acres than on deferred rotations. Of all the grazing systems samples, deferred rotation pastures were least preferred by nesting and brooding grouse. Although the stocking rate of the deferred rotation systems was less than rest rotation systems, the ungrazed forage was lower. Grazing all pastures each year apparently leaves insufficient residual vegetation to meet minimum grouse nesting/brooding requirements. Nest location and nest fate as related to residual cover was dependent on approximately 1,000 lbs. of forage/acre no matter which grazing system was sampled. The results of the Rice and Carter (1982) study led them to recommend that grazing management within the Fort Pierre National Grasslands consist of rest rotation and winter pasture grazing systems. An important point was that using the rest rotation system, rancher permittees could still maintain livestock allocations while producing over four times as many grouse as deferred rotation systems. They recommended that deferred rotation grazing systems be discontinued on the Fort Pierre National Grasslands because the minimum grouse cover requirements of approximately 1,000 lbs/acre forage left ungrazed cannot be attained utilizing this system. Certainly the FPNG are different from the SNG. The range sites there are mostly composed of clayey and shallow-clay soils. Average primary productivity is lower. However, these differences do not rule out the importance and perhaps applicability of their conclusions about grazing systems.
Grazing systems are not a panacea that can solve all problems met in managing grazing lands, such as providing adequate residual cover for wildlife species. Heady (1974) concluded that grazing systems have worked only when the graziers quit overgrazing! After reviewing numerous studies, Van Poollen and Lacey (1979) concluded that adjustments in animal numbers have a greater effect on herbage production than do grazing systems. Wilson (1986) as one of his principles of grazing systems for rangelands has stated, "The total stocking intensity is the most important factor affecting rangeland productivity and stability." This should not be overlooked in the case of the SNG. No grazing system will work (i.e. provide adequate residual vegetation) if the stocking rate is too high. McDaniel (personal commun.) has provided some very interesting data apropo to this point (Figure 4). McDaniel states "there is a direct 'cause and effect' on potential prairie grouse nesting cover when annual AUMs (utilized) are reduced from 50,000 to 10,000." Although these data are from the Valentine National Wildlife Refuge, there may well be more similarities to the SNG than there are differences.
The accepted fact that the cattle grazing today are significantly larger
than the 1,000 lb. standard needs to be considered. Larger cattle use more
AUMs. Quite possibly the acres/AUM on the SNG needs to be revised upward.
This is a sensitive issue which deserves careful consideration. Common sense
tells us that both livestock production and prairie chicken production (as
well as other desirable plant and animal populations) cannot be simultaneously
Figure 4. The relationship of prairie chicken populations to grazing intensity. (From Len McDaniel, personal commun.)