Northern Prairie Wildlife Research Center
We also must be clear about the meaning of biodiversity. Preserving diversity means protecting the various forms of life and the habitats and processes that support them (Keystone Center 1991). It does not mean maximizing local species diversity. Adding trees to a prairie landscape, for example, will increase local biodiversity by providing new habitat for such species as brown thrasher, gray catbird, song sparrow, common grackle, and western kingbird. But it will not enhance their viability, for these species are widespread, common, and can thrive independently of happenings on the prairie. Conversely, the addition of trees to grasslands may reduce the viability of true prairie birds, species whose future does depend on the grasslands (e.g., Knopf 1994).
Further, we should contrast management of prairie landscapes from that of cropland landscapes. Highly cultivated areas are generally depauperate of bird species, except certain "weedy" ones or those that favor sparse cover (Best et al. 1995). In such situations, adding trees and shrubs, and managing roadsides for wildlife will enhance the local species diversity and provide a more aesthetically pleasing environment without negatively affecting other species. In a true prairie situation, however, those same practices could be detrimental.
One promising development is the pairing of two major conservation partnerships, the North American Waterfowl Management Plan, whose goal is the restoration of waterfowl populations and habitats in North America, and the Partners In Flight program, which emphasizes neotropical migrant landbirds. The Waterfowl Management Plan works primarily through geographically based joint ventures. The Lower Mississippi Valley Joint Venture recently completed a habitat plan that encompasses neotropical migrant birds and shorebirds, as well as waterfowl. The Prairie Pothole Joint Venture has begun a similar effort. The initial emphasis will be to identify species of special concern, determine how management activities affect those species, and propose appropriate management strategies.
Unlike the situation with the Waterfowl Management Plan, defining population objectives for nongame species will be virtually impossible. Reasonable estimates of population size for those species are almost totally lacking. The BBS monitors trends in certain populations with some accuracy, but is imperfect for many others. Further, the often-low philopatry (McNicholl 1988) in many grassland and wetland birds argues against area-specific objectives. For example, Conservation Reserve Program fields in Eddy County, North Dakota, supported an average of only 0.03 pairs of Le Conte's Sparrows per 100 ha during 1991-1993. In 1994, because of extremely wet conditions, the density jumped to 21.47. Those conditions persisted into 1995, when the density continued to climb to 73.27 (unpubl. data). Other grassland and wetland species exhibit similar dynamic responses to precipitation, wetland conditions, temperature, and local land use such as burning and grazing. Establishing specific population objectives for particular habitats is not feasible; our approach should be to provide the habitat base thatwhen other environmental conditions are rightwill support desired and sustainable populations.