Northern Prairie Wildlife Research Center
Owners and operators of farms can implement agricultural practices that will benefit NTMBs on midwestern farmland. Many farmers appreciate having non-pest bird species on their farms and nearby. If farmers are forced to choose, however, between economic survival and having wildlife to observe and hunt, they will choose survival. Even in situations in which economic survival is not at stake, farmers will consider costs. It is in these situations where information and education (e.g., university extension) may make the difference in favor of wildlife generally and NTMBs specifically. Here we take the practical approach of recognizing that recommendations for farmland must be aimed at a broad audience that includes private landowners as well as professional wildlife managers. We offer three objectives that we believe will have broad support, review a general framework that likewise should have broad support, and summarize specific recommended modifications to current agricultural practices.
A primary objective of a conservation strategy for NTMBs in midwestern agricultural landscapes should be to conserve the remnants of prairie and savannah that still exist. Most of the prairie has been lost (Samson and Knopf 1994), increasing the value of the remnants. Although restoration of midwestern prairie and savannah ecosystems on a large scale is impractical, the remnants can be used for biological investigations, ecological education, and core areas for additional restoration. Although the persistence of grassland and open-woodland birds in the Midwest may not depend on these remnants, it is important for the conservation of biodiversity in general to save or restore representative natural ecosystems with a large proportion of their native flora and fauna. Of similar importance are the remnant woodlands, riparian areas, and wetlands required by a variety of bird species (Best et al. 1995, Table 1).
A second objective of a conservation strategy should be to ensure the population viability of species that are (1) listed under the Endangered Species Act (ESA), (2) listed by individual states, or (3) are of special concern to managers because their populations are declining or vulnerable (USFWS 1995). Forty-one of these might occur in midwestern farmland (Table 1). Investments that could prevent listing of additional species under the ESA may be economical in the long run, given the costs of listing, preparing recovery plans, etc. Beyond this practical reason, drastic population declines of rare species will result in loss of these species from some ecosystems, which may affect ecosystem functioning and be undesirable for other reasons (Wiens and Dyer 1975, Ehrlich and Mooney 1983, Saunders et al. 1991, Chapin et al. 1992, Baskin 1994).
A third objective should be to identify priority species or groups of species beyond those identified under the second objective. A different conservation strategy for these NTMBs might be called for, depending on whether the primary concern is for reversing population declines or for promoting biodiversity. Some species may require large blocks of grassland habitat (Herkert 1994), and others may benefit from increased availability of edge habitat in the form of strip cover. Ideally, management can benefit all groups (Tome et al. 1994).
Identification of sources and sinks (Wiens and Rotenberry 1981, Pulliam 1988) is an important step in implementing a conservation strategy for NTMBs in farmland (Rodenhouse et al. 1993). This step has been taken for forested habitats in the Midwest (Donovan et al. 1995). Many managers now understand that creating attractive habitat may not necessarily benefit target species if that new habitat is a sink for those species. The review by Rodenhouse et al. (1993) of nest success in farmland indicates that few species are known to be reproducing at levels sufficient to balance estimated mortality. Even the nest success estimates in CRP fields and moderately grazed pastures, reviewed in the "Idling cropland" section, are not encouraging.
After sources and sinks have been identified, habitat, land-use, and landscape features that distinguish them can be examined to determine which features contribute to differences in vital rates. Such analyses will lead to recommended practices that will change the attractiveness of sources and sinks or increase individual fitness in them. Simulation modeling can be useful in evaluating potential actions (e.g., Cowardin et al. 1983). Finally, after actions have been taken, the status and trends of target species or guilds should be monitored to evaluate the results. All of this can be done in the context of a comprehensive framework for conservation and management planning (Freemark et al. 1993, 1995). A major limitation of this process is our incomplete understanding of factors affecting population dynamics and ecosystem functions in agricultural ecosystems.