Northern Prairie Wildlife Research Center
Land Management Practices
Many management practices can be beneficial to grassland bird habitats. Because of the importance of idle grassland habitat it is generally important to rotate management through a given tract or area so that no more than approximately one-third of the land area is disturbed by any management technique or techniques in a given year (Herkert et al. 1996). Rotation of disturbancessuch as mowing, grazing, harvesting, and burningthrough subunits within a habitat block helps assure that some residual vegetation is always available for those species that require it. Rotation, especially in native grassland remnants, also provides refugia for potentially fire-vulnerable invertebrates and other fauna. It appears that a management subunit (i.e., the portion of a grassland block disturbed by management) may need to be at least 75 acres in size to maximize benefits for grassland birds (Herkert et al. 1996). In Wisconsin, most blocks of grassland habitat are not currently large enough to allow for subunits this size.
On private lands used for production agriculture, there are few recommendations that are currently both feasible to the farmer and beneficial to grassland birds. For example, delaying mowing until after 15 July is not likely to be considered by many dairy farmerseven with compensationunless they are willing to let some fields go for use as feed for dry cows or other animals that do not require high-quality forage or if they want to let legumes re-seed themselves. One suggestion that has some merit is to cut hayfields from the inside out to allow escape routes for fledglings (Figure 7). In addition, locating idle nesting coversuch as old fields or set-aside landsadjacent to hayfields provides alternate habitat for species that renest after mowing-induced failure of first nest attempts (Warner and Etter 1989).
On public and private lands managed for wildlife conservation purposes, it is advisable to delay mowing until after 15 July. Mowing after this date will allow most species a chance to raise at least one brood. However, in cases where late-nesting species such as dickcissels and sedge wrens are being managed for, mowing should be delayed until early August. If more than one mowing is conducted or if mowing is required after the breeding season for some other purpose, the last mowing of the year should generally be early enough to promote some fall regrowth, which provides residual vegetation cover the following spring. This means mowing should be done by early September (for cool-season grasses) or early August (for warm-season grasses) in most years.
Grassland birds respond to mowing in various ways:
Early spring (March and April) burning affects grassland bird species in different ways. In the breeding season immediately following the burn, some species do very well in burned areas, while others do not:
Over time, short spring burning rotations (every 1-2 years) reduce or remove woody vegetation and therefore lower the quality of habitat for species requiring shrubs or small trees. As shown above, one-year rotations also discourage species that require residual vegetation in the spring. Rotations of at least five years and longer tend to favor and maintain a woody component, such as upland shrub communities, and residual vegetation. Bird species that do not have significant requirements for litter or standing residual vegetation in spring will likely do well under short rotations, and most species appear adapted to moderate-length (3-5 year) burning rotations (Herkert et al. 1996).
Native warm-season grass pastures can provide good habitat for a variety of grassland bird species (Skinner et al. 1984) and have the advantage of being left ungrazed until relatively late in the nesting season, when the forage quality of cool-season grass pastures has declined. However, warm-season pastures may require special management to maintain the warm-season grasses over time, such as by limiting the period of intense grazing in summer and by burning in late April or early May (R. Henderson, personal communication).
Fall grazing should be stopped by early- to mid-September for cool-season grasses or early August for warm-season grasses, to allow for vegetation regrowth before dormancy sets in. The presence of several scattered shrubs or small trees, especially thorn-bearing species, increases the value of pastures as potential loggerhead shrike habitat.
As a general rule, bird species that prefer short vegetation occur in heavily grazed pastures, just as species preferring moderate and tall vegetation inhabit moderately and lightly grazed pastures, respectively. However, because pastures are often not grazed evenly, there is a likelihood that several ranges of vegetation height-density will be represented in a single pasture, especially large ones. The following are generalizations about species' responses to grazing from research in Wisconsin and the midwest:
Herbicides are typically used in wildlife management for controlling noxious or aggressive weeds and woody vegetation. These chemicals can cause changes in vegetation structure, which, as described above, affect habitat suitability for birds. Chemicals that biodegrade quickly should be used in preference to those that do not. See also "Conventional Cropping Practices," below.
Planting and Restoration
It is difficult to describe a seed mixture or seeding rate that guarantees a certain type of vegetation structure, because of variability in soil type and moisture, establishment techniques, and annual variation in precipitation. However, a general approach to lower vegetation height and density and to increase structural diversity is to lower seeding rates:
It is also important to establish forbs in managed grasslands because they diversify structure and invertebrate resources. Several bird species such as dickcissel and savannah sparrow are most abundant in fields with a strong forb component. Reducing grass seeding rates, along with mowing or burning occasionally in the summer or fall, also helps encourage the forb component of a planting. Moreover, enough forb seed should be added to most mixes to result in at least 10% forb cover. In most cases, 10,000-20,000 forb seeds per acre should result in a noticeable forb component, as long as grass seeding rates do not exceed those recommended above (R. Henderson, personal communication). Forb seeds vary greatly in size and weight; therefore, an average seeding rate cannot be provided. For more detailed information on seed mixes and seeding rates for native grasses and forbs under differing soil moisture conditions, see Henderson (1995).
Planting a mix of grass species is preferable to planting monocultures, and native grasses are generally preferable to non-native cool-season grasses, although birds do not require them. Native grasses and forbs are also better than non-native species for prairie invertebrates (Henderson and Sample 1995). However, there may be specific cases where monocultures can be used, such as targeting habitat for sedge wren or Henslow's sparrow.
Restorations of native grasslands should be targeted for areas in the state that were grasslands in presettlement times (Henderson and Sample 1995).
Conventional Cropping Practices
The most valuable agricultural habitats for grassland birds are old fields, lightly to moderately grazed pastures, fallow fields, wet meadows (undisturbed or periodically cropped or grazed fields), and late-cut grass hay and mixed grass and legume hay. None of these habitats is as common as those described above.
Cropping systems that reduce pesticide and inorganic fertilizer usesuch as through integrated pest management and measuring soil requirements, respectivelyare preferred over systems that depend heavily on these chemicals. Both inorganic fertilizers and pesticides reduce the invertebrate food base and may negatively affect young or adult birds. Pesticides can also simplify the vegetation structure and plant species composition in crop fields (Rodenhouse et al. 1995).
Alternative Cropping Practices
Conservation tillage. Conservation tillage has been shown to provide better nesting habitat for more grassland bird species than conventionally tilled fields (Warburton and Klimstra 1984, Basore et al. 1986). The presence of crop residue on the soil surface also supports higher numbers of invertebrates than conventionally tilled fields, therefore increasing food resources. However, increased mechanical cultivation and possibly pesticide use for weed control in conservation tillage fields may cause them to be ecological traps (Best 1986). Conservation tillage systems that reduce the need for additional pesticide use, such as ridge-till or the use of integrated pest management, are preferred for row crop grassland bird habitat.
Intensive rotational grazing. This increasingly popular practice (Undersander et al. 1991) is not beneficial to most grassland bird species because of intensive trampling from cattle and short rest periods between grazing events (Paine et al. 1996a, Temple et al. n.d,). However, when incorporated into farms with adjacent grasslands that are not cut or grazed until after the peak breeding season, rotational grazing may boost overall grassland bird productivity above that of conventional farms (Temple et al. n.d.).
Alternative Crops. At present, few alternative crops have been produced in large enough areas in Wisconsin to assess their value as grassland bird habitat. In Iowa, experimental strip intercropping of corn, soybeans, oats, and legumes produces higher bird abundance than conventional row crops but may function as an ecological trap by attracting birds to settle in a habitat with a low rate of nest success (Stallman and Best 1996). Native warm-season grasses grown as biomass energy crops can improve grassland bird diversity compared to conventional row crops (Paine et al. 1996b). Research on other crops and cropping practices that are both beneficial to farmers and birds is currently being conducted.
Annual set-asides. Annual set-asides, such as Acreage Conservation Reserve (ACR) fields enrolled in the now-defunct USDA Feed Grain Program, received moderate use from grassland birds of management concern (Sample 1995) and provided higher quality habitat than row crops. Some set-aside fields such as those planted to small grains suffered because regulations allowed for late planting during the breeding season, while others such as grass and legume mixtures suffered from early mowing. Although annual set-aside programs are currently being phased out, grassland birds will benefit in the future more from multi-year programs that encourage diverse plantings of grasses and forbs and that do not release such plantings for cutting before 15 July. Bird communities in annual set-asides are similar to those listed in Appendix E and Table 1, under alfalfa hay, small grains, and fallow fields.
Long-term set-asides. Habitat established under programs such as the CRP has proven to be valuable to grassland birds in Wisconsin. In CRP fields in the southern part of the state, several species of management concern, including dickcissel, vesper and grasshopper sparrow, bobolink, and western meadowlark have been found in similar densities to those in other preferred habitats (Sample 1995). Early release of CRP fields for haying due to drought conditions during the bird breeding season and emphasis on seed mixtures aimed at the creation of tall, dense cover, however, have limited the CRP's value for grassland birds. We make the following recommendations for improving habitat quality in long-term set asides such as CRP land:
Cut-overs. Recently clearcut or burned-over forest land provides habitat for many grassland speciesmainly those that require cover of shrubs or other low woody vegetation (see Appendix E and Table 1). If blocks of cut-over habitat are big enough, they may provide habitat for sharp-tailed grouse. Cut-overs remain suitable for some grassland and shrub-grassland species until most of the regenerating trees become taller than 10 ft and exceed roughly 50% cover. Large blocks of short-rotation, even-aged forestry can be targeted for stands at the edges of open, diverse, and brush prairie barrens, firebreaks, or other grassland openings to increase the effective size of grassland habitat (Mossman et al. 1991).
Firebreaks. Wide (440 yd), herbaceous (or heath-dominated) firebreaks in the northern forest provide grassland bird habitat and may even serve as important corridors between grassland openings, such as in the barrens area of northwestern Wisconsin. Many grassland species, including sharp-tailed grouse, use such firebreaks (Gregg 1987, Niemuth 1995).
Conifer plantations. Young conifer plantations are most useful to grassland bird populations when the trees are less than 10 ft tall. Avoid locating these plantations in open grassland landscapes. Typical bird communities of young conifer plantations are listed in Table 1.
agricultural habitats are subject to farming-related disturbances during
the breeding season that may lower grassland bird nesting success. The
conservation of undisturbed or idle habitats is therefore important.
is generally important to rotate disturbance through a managed field so
that no less than two-thirds of the land area remains idle in a given
of vegetation structure and cover types should be promoted at a variety
is important to establish forbs in managed grasslands because they diversify
structure and invertebrate resources.
most valuable agricultural habitats for grassland birds are old fields,
lightly to moderately grazed pastures, fallow fields, wet meadows, and