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Management of Agricultural Landscapes for the Conservation of Neotropical Migratory Birds

Conservation Strategies

Specific Recommendations

Rodenhouse et al. (1993) made the insightful observation that farming might develop along two tracks. Small, owner-operated farms would predominate close to urban centers where farm families could obtain supplemental income. These farms would provide habitat for many NTMBs because expensive inputs (large machinery, fuel, inorganic fertilizer, and pesticides) would be minimized and farming would be diversified. Large, externally owned farms would exist in rural areas with the most productive soil. These would be intensively managed and provide little non-crop habitat. These tracks certainly seem reasonable, considering current economic conditions in the Midwest.

Agricultural practices on larger farms may best be influenced by modifying agricultural programs and policies. These farms can be expected to attract species nesting in cultivated fields: horned larks, vesper sparrows, and killdeer. Although these species are not common in cropland (Table 1), their cropland habitat is very extensive. Populations of these species large. Monitoring of population trends of these species should continue. As long as their populations are relatively stable (Johnson and Schwartz 1993b), these species should not receive high conservation priority. Vesper sparrow populations have declined recently in parts of the Midwest, according to data from the North American Breeding Bird Survey, and had low nest success in Iowa (Perritt and Best 1989).

Smaller farms should be encouraged to enhance the attractiveness of their land to NTMBs, especially grassland birds that have declined in recent decades, such as grasshopper sparrows and bobolinks. Long-term set-aside, such as the CRP, provide much of the grassland habitat in the Midwest today and should be encouraged. A wide variety of other species, including woodland species, also can benefit from farmland (Table 1). The following recommendations are organized by agricultural practice, as covered above.

Cultivation. Tillage should be minimized. Rodenhouse et al. (1993) recommended that crop residue be retained on the soil surface, which could be done by reducing the number of times a field is cultivated annually and by using subsurface tillage where appropriate. A greater variety of NTMBs may be attracted by increasing the diversity of crops grown, especially if the structure of the vegetation is quite different. Crop diversity also will contribute to sustainable agriculture (Barrett et al. 1990).

Grazing. Grazing is not incompatible with a diverse avifauna. Moderate grazing of pastures may enhance local habitat diversity. It has been suggested, however, that public grasslands managed for wildlife should benefit species that prefer habitat that is in relatively short supply, that is, grassland that is not frequently grazed or hayed (Kirsch et al. 1978). This recommendation could be extended to private land in the Midwest. Each grassland species has a particular kind of preferred vegetaion for nesting (Owens and Myres 1973, Skinner et al. 1984), facilitating management for particular groups of species. Further grazing recommendations are in Herkert et al. (1996).

Haying. Haying appears to be a major problem for NTMBs because hayfields have low nest success (Frawley 1989, Bollinger et al. 1990). They are highly attractive to certain species, but the cutting interval is usually too short to allow complete nesting cycles. Rodenhouse et al. (1993) recommended that spring mowing be delayed as long as possible, nighttime mowing be avoided, and the intervals between mowing be as long as possible. Additionally, hayfields with warm-season grasses should be encouraged because they would be cut later in the year than alfalfa. Further recommendations are in Herkert et al. (1996).

Idling cropland. Idled cropland would seem to require relatively little management because it already attracts a variety of species. Practices such as mowing or burning, however, could modify many areas and change the composition of the avifauna. Mowing during the nesting season can lower nest success substantially. It may be possible to enhance bird reproduction and survival by changing the amount and configuration of idle land; nest success may be higher in block habitats than in linear ones with proportionately more edge habitat. In a Minnesota study, nest success was lower near woody edges of tall-grass-prairie remnants than it was farther from such edges (Johnson and Temple 1990). Finally, if certain kinds or configurations of idled cropland are found to be source habitats, they should be strongly encouraged to counteract the many apparent sinks in agricultural landscapes.

Patterson and Best (1996) examined bird use of CRP fields that differed in structure and composition of vegetation and made recommendations aimed at benefiting grassland birds. The species composition of the vegetation should be based in part on vegetational attributes that attract birds. A wider variety of planted species than has been used in the past would enhance bird use. Mowing of weeds should be done after the peak of the nesting season. Some large tracts of habitat should be maintained for the benefit of area-sensitive species. Other recommendations could be added to their list. Grazing may enhance species richness if the structural diversity of the habitat is increased. Prescribed burning, every few years, is often recommended for other grassland habitats to maintain attractive nesting cover, and presumably would benefit birds using CRP fields. Multiple-year programs, such as the CRP, appear to offer many more benefits to NTMBs than annual set-aside programs. Grassland cover that is at least a year old is established well enough in the spring, when migratory birds arrive, to attract breeding pairs. After a few years, vegetative and sexual reproduction by plants fills in gaps from the initial seeding, increasing the height and density of vegetative cover.

Maintaining strip cover. Recommendations for strip cover depend on whether management is intended to favor grassland species or edge species. Management for the former should favor herbaceous cover. The benefits to NTMBs of permanent herbaceous cover can be enhanced by changing common practices. Timing of mowing of grassed waterways should be considered. Because peak nesting in grassed waterways occurred in July in Iowa, Bryan and Best (1991) recommended that mowing in waterways be deferred until the end of August or early September. Fall mowing is not recommended because residual cover would be reduced in the subsequent winter and spring, and annual mowing is discouraged (Bryan and Best 1994).

Beck (unpubl. data) found several factors that decreased wildlife use of grassed-backslope terraces, such as backslope steepness, poor grass stands, narrow width, grazing, and herbicide drift. He suggested that improved management might involve flattening backslopes, improving grass stands, improving grazing management, and planting alternative vegetation.

If herbaceous vegetation on roadsides is mowed, it should be mowed in mid-to-late August (Camp and Best 1993). Also recommended is prescribed burning in the spring every 3-5 years. Both mowing and burning should be conducted in blocks to ensure that some portions of roadsides are undisturbed at any time. Fencelines should be retained along roadsides because roadsides with fencelines are less susceptible to agricultural encroachment and fencelines provide singing perches for birds. Mowing roadside shoulders provides nesting habitat for some species, but mowing should be restricted to early spring and late summer to reduce nest losses.

An adoption model for roadside (and other) habitat management involves farm operator attitudes and perceptions (Warner 1983). Warner (1992) made the following roadside management recommendations for grassland birds: (1) fescue and bluegrass (Poa) sods should be seeded to brome-alfalfa and/or native grasses and forbs, (2) mowing should be delayed until after 1 August, (3) widths of roadside tracts should be maximized where possible, and (4) the establishment and protection of woody plants should be encouraged. In areas where brown-headed cowbirds are abundant, of course, the effect of woody plants on frequency of brood parasitism will have to be considered carefully. The prescribed burning recommended by Camp and Best (1993), which would slow the establishment of woody plants, could be used in areas where woody plants were not desired. They also noted that bird use of roadsides with well-established native vegetation has not been evaluated. Such roadsides may become more abundant in the future as the agencies charged with managing roadside vegetation seek methods that will benefit wildlife and minimize invasion of weeds.

Managing for breeding, edge species should be focused on providing diverse habitat in which nest success can potentially be high. Fencerows should be >3m wide, according to the recommendation of Shalaway (1985), who worked in Michigan. This would allow for greater shrub/tree growth and potentially reduce the likelihood of nest predation. Farther west, where brown-headed cowbirds are more abundant, the possible enhancement of habitat for this species would have to be considered. Shalaway (1985) also suggested that selective mowing and woodcutting in fencerows can create a mosaic of vegetation types attractive to a variety of birds. He also recommended retaining or creating at least 1-2 large snags per km of fencerow. Artificial nest-boxes may attract eastern bluebirds and tree swallows (Robertson et al. 1992), both NTMBs.

Management recommendations for shelterbelts, given by Yahner (1983a), include: establish shelterbelts at least 0.6 ha in area and 8 rows in width, consider proper spacing within and between rows, use a diversity of plantings, discourage livestock grazing, discontinue mowing and cultivation after the shelterbelt becomes established, and retain snags as nesting and foraging sites.

General. Our final recommendation is that biologists and managers strive to improve their working relationships with private landowners and the organizations that represent them. The concept of benefiting NTMBs in agricultural landscapes is different from much of traditional wildlife management, which has focused on managing land controlled by state and federal governments. Those seeking to benefit NTMBs can learn from those who have sought to benefit ducks and upland game species, most of which occur on private land. Many game managers have learned the value of education, outreach, and attention to landowner concerns. Progress may require compromise and consideration of large-scale solutions, such as influencing agricultural policy. The recent efforts to renew the CRP brought together many wildlife and farming organizations that shared a common interest. Serious consideration has been given to the major effects of agricultural policies on wildlife in agricultural landscapes (Risley et al. 1995). With enhanced communication, sound science, and a common conservation strategy, we are confident that farmers and wildlife can continue to coexist in the Midwest.

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