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Agricultural Grasslands

Kennebunk Plains, Maine
Photo by Peter Vickery

Large Grasslands

Managing Large Grasslands for Grassland Birds

Introduction
Value of Large Grasslands to Wildlife
Management of Grasslands on Conservation Lands
   Grazed Grasslands
   Mowing Large Grasslands
   Burning Large Grasslands
Management of Grasslands at Airfields for Grassland Birds
Management of Capped Landfills for Grassland Birds
Grassland Restoration

Introduction

Large grasslands are disappearing rapidly in the Northeast. Once abundant in the 1800s when land was cleared for farming, they are now rapidly shrinking because of reversion of farms to forest, changes in agricultural technology, movement of farms to the West, and an increase in human population. Native grasslands along river floodplains and coastal New England are similarly threatened by agriculture and development. Large grasslands are home to a diversity of wildlife: mammals, butterflies, and birds-including some of our rarest grassland birds -- grasshopper sparrows, upland sandpipers, and northern harriers. These birds need large contiguous patches of grassland habitat for successful breeding. In some areas, airports and military bases provide the best remaining habitat.

The following information provides recommendations for organizations owning or managing grasslands on how to maintain those areas for the benefit of grassland birds and other wildlife. It also provides suggestions and management options for grasslands at airports, where management for grassland birds and wildlife is not the first priority but can be incorporated into routine maintenance.

Value of Large Grasslands to Wildlife

Short-Eared Owl
Photo by Roger S. Everett

Large grasslands provide crucial habitat for many species of grassland birds throughout the year. Bobolinks and eastern meadowlarks build nests, raise young, and forage in small and large hayfields, meadows, and pastures during the summer months. However, large grasslands, if appropriately managed, can provide habitat for rare grassland birds, such as upland sandpipers, grasshopper sparrows, and northern harriers (all listed as threatened or endangered in most Northeast states). These birds will only nest in large contiguous grasslands that contain a grassland mosaic, including mowed areas and meadows of tall grasses and wildflowers.

These areas are also important for birds of prey, such as American kestrels, northern harriers, and red-tailed hawks, that live in or near grasslands and rely on these habitats for hunting insects and small mammals.

In the fall, expansive grasslands provide food to attract migrating sparrows, larks, and warblers. Large flocks of waterfowl and shorebirds sometimes feed in flooded portions of fields during migration. Some songbirds that breed further north, such as snow buntings, feed in large flocks in these grasslands during the winter months. Large grasslands are beneficial to two rare species of owls, short-eared owls and snowy owls, during the winter.

Snowy owls regularly visit large airports and vast frozen wet meadows that provide the look of a tundra when frozen and offer plentiful mammals and songbirds for hunting. Short-eared owls once bred in larger numbers on coastal islands in the Northeast but have diminished to a few remaining pairs. However, many still settle in the Northeast's remaining large grasslands during the winter. Rough-legged hawks breed in the Arctic but move south in the winter and are often seen feeding in open fields and marshes in the Northeast.

In addition, grasslands provide habitat for a variety of other wildlife, including mammals and insects. Small mammals that inhabit fields, such as meadow voles and meadow jumping mice, are an important food source to many birds of prey. Larger mammals, such as white-tailed deer and red foxes, regularly visit grasslands for feeding. Butterflies, such as tiger swallowtails and monarchs, can be found in fields feeding on the nectar of wildflowers.

Two species of grassland birds, grasshopper sparrows and upland sandpipers, are declining rapidly in the Northeast. However, with increased conservation efforts and changes in some management practices, large grasslands in this region can provide breeding habitat for these rare birds.

Management of Grasslands on Conservation Lands

Grazed Grasslands

Cattle, sheep, and horses have different food preferences; their grazing has effects on the different vegetation structure of pastures. Many grassland birds in the Northeast tolerate and benefit from light grazing because it creates a mosaic of grass heights and structures, removes ground litter, and benefits bunch grasses. Light grazing also allows the development of wildflowers and scattered shrubs. However, intensive grazing leads to a loss of plant diversity and cover for wildlife. Large grasslands can be managed in a rotational system to benefit breeding birds.

Recommendations

In grazed pastures with nesting birds, keep approximately 40 percent of the vegetation cover at a minimum height of 8 to 12 inches or at "knee height" with scattered forbs until August 1. This can be achieved by rotational grazing. During the most critical nesting period (June 1 to July 15), keep cattle off fields with dense populations of grassland birds. Leave some pastures undisturbed in May and June when birds are arriving and setting up territories.

Avoid overgrazing fields. Overgrazing creates excessive bare ground that can cause erosion, reduce plant and invertebrate diversity, and lead to trampling of ground-nesting birds.

Experiment with different grazing regimes in your fields to determine what intensity of grazing and rotational system works best to provide wildlife habitat. This will vary from site to site depending on the type of vegetation, soil and moisture conditions, and the size of the livestock herd. Manipulating the intensity, frequency, and duration of grazing through fields preserves upland or wetland vegetation, protects stream bans from erosion, minimizes soil compaction, and benefits nesting grassland birds.

Mowing Large Grasslands

Photo by Peter D. Vickery

Hayfields and meadows support a rich diversity of grasses, wildflowers, and invertebrates that are important for breeding grassland birds. Old hayfields, not replanted for at least eight years, are favored by some birds (such as bobolinks) because of the developed ground cover and a greater variety of grasses and other plants. Mow every one to three years to maintain fields in grasses and prevent growth of woody vegetation.

Timing of mowing is crucial to the survival of nesting grassland birds. Early and frequent mowing destroys nests and young. Therefore, mowing after August 1 is recommended if increasing grassland bird habitat is a management goal.

Recently, many grasses native to the Northeast have been replaced by fast-growing grasses that can be harvested several times during the summer to provide high-quality hay for livestock. This increased production, plus the use of fertilizers and modern machinery, has created grasslands with little diversity. Switching grass varieties or altering mowing practices can benefit breeding grassland birds.

Recommendations

Avoid mowing areas with ground-nesting birds before August 1. It is common to see young birds in fields by late June, but cutting should be avoided because some species, such as eastern meadowlarks and grasshopper sparrows, raise a second brood later in the season, and the young fledge in late July.

Be aware of where grassland birds are nesting in fields. If mowing is essential prior to August 1 (such as in fields leased to farmers for hay), try to avoid areas where birds are frequently seen or leave small patches such as edges or strips unmowed as nesting areas. Even when young birds appear to have left the nest, small unmowed patches are still needed to provide cover and feeding areas for the remainder of the summer until they migrate south.

Limit mowing to every one to three years in fields not harvested for high-quality hay. It is not necessary to mow every year for grassland birds. Not mowing a field in a given year or delaying mowing until late August will allow development of late-blooming wildflowers and will benefit butterflies.

Maintain some areas of fields with patches of bare ground. Killdeers and horned larks, for example, require patches of bare ground for nesting and feeding. This can simply be in areas where grass growth is poor due to soil conditions, or in small areas with intensive grazing. Bare ground can also be exposed by removing hay from fields where thatch (compressed dead grass) becomes thicker than two inches.

Choose fields that are not used for hay production for wildlife habitat. Mowing high-quality hayfields in early June will discourage birds from nesting in those areas. Birds that do attempt to nest in these fields will probably fail due to mowing activities. In time, birds are not likely to return to fields where their nests were destroyed. However, if adjacent unmowed fields are available, birds can shift from high production hayfields to those areas and renest. Fields mowed frequently can still provide important feeding areas for upland sandpipers and other birds that nest in adjacent unmowed fields.

Use conservative mowing practices where possible. These may include practices such as raising mower blades to six inches or more (may prevent the destruction of some nests and young in early mowing); avoiding night mowing because this often kills or injures roosting birds and young; using flushing bars on haying equipment to move birds hiding in the grass.

Manage multiple contiguous fields for conservation. Four adjacent fields are better than four isolated fields. Multiple adjacent small fields can provide the "look" of a large grassland, especially if hedgerows are removed and planted in grasses. This continuous landscape is necessary for grasshopper sparrows and upland sandpipers, which require large grasslands. Multiple contiguous fields can be managed through rotational mowing and/or burning to provide a mosaic of grassland types and, therefore, to attract a greater diversity and abundance of grassland birds.

Burning Large Grasslands

Burning reduces buildup of dead vegetation, adds nutrients to the soil, rejuvenates plant growth, and helps prevent the spread of woody vegetation. Hayfields that develop a thick layer of thatch are usually not used by nesting birds because they cannot effectively run on the ground to escape predators or forage for food. Burning is particularly beneficial on large grasslands, where burns can be rotated over smaller patches each year, leaving some areas unburned to provide nesting habitat for breeding birds. Most grassland birds will reoccupy burned areas within one or two years following a burn.

Recommendations

Burning every two to six years provides the best habitat for grassland birds. Do not burn more than 50 percent of a grassland within a year (ideally 20 to 40 percent annually), or, if possible, provide adjacent unburned grassland habitat for nesting birds during the burn year.

Burning in early spring (before the arrival of birds in mid-May) is most beneficial to vegetation and nesting birds.

Careful planning is necessary before burning. Most grassland burns occur between mid-March and the end of April, after snow melt and before greening and bird nesting. The timing of the burn must also be done with consideration of relative humidity, wind conditions and direction, air temperature, and fuel conditions. Burn designs must incorporate existing firebreaks (roads, lakes, and streams), or firebreaks must be designed. Adjacent landowners should be notified prior to burning.

Contact your local fire department for guidance and permits before burning a field. "Burn bosses," individuals trained and certified in prescribed fires, from local universities or conservation organizations (see Table 4 for list of local Audubon/conservation societies) can be contracted to consult and manage prescribed burns.

On areas larger than 100 acres, rotate burning on 20 to 40 percent of the area annually to provide a mosaic of grass heights and structure.

Management of Grasslands at Airfields for Grassland Birds

Grassland at an Airfield
Photo by Andrea Jones Caption

Mowing is essential in grasslands surrounding airfields to prevent growth of woody vegetation and comply with airport safety regulations. However, mowing can be manipulated to reduce mowing costs and benefit grassland birds. Ground-nesting birds found nesting at airfields should not pose a threat to aircraft because of their small size and low direct flight; in addition, managing for these species by leaving some areas unmowed during the summer can help discourage large flocking birds that prefer fields of very short grass, such as gulls, crows, and Canada geese, and are more likely to damage aircraft.

Recommendations

Restrict mowing during the breeding season. (May 1 to July 31) on portions of airfields not directly adjacent to runways and taxiways.

Maintain 50-foot mowed strips along taxiways and runways throughout the breeding season to discourage birds from nesting in these areas. Short grasses along runways can also help reduce insect populations that can cause problems to aircraft. Other mowed strips, such as along roadways, are used by upland sandpipers and other birds for feeding.

Minimize training activities during the breeding season in nesting and brood-rearing fields.

Observe and mark locations of nesting birds and avoid mowing those areas until birds have fledged. This may be achieved by grounds maintenance personnel, or, if this is not feasible, contact local Audubon society biologists (see Table 4, Agencies or Organizations Specializing in Agricultural Land Management Issues for list of Audubon/conservation societies) to survey and mark airfields for nesting birds.

Burning grasslands at airfields can be used as a management tool to benefit nesting birds. Taxiways and access roads at airports provide ideal firebreaks. See section above for specific recommendations on burning.

Management of Capped Landfills for Grassland Birds

As landfills are closing and becoming capped throughout the Northeast, there is the potential to create substantial new grassland habitat. Landfills are capped by plastic liners, topped with one to two feet of topsoil, and then planted with grasses. Landfills must be kept in grass in order to prevent deep-rooted trees and shrubs from puncturing the plastic liner. These areas often create nesting habitat for grassland birds. Ideally, landfills larger than 30 acres will provide habitat for the greatest diversity of birds. Although landfills five acres or smaller are not likely to be attractive to nesting grassland birds, they can provide habitat for butterflies and other invertebrates and feeding areas for migrating birds.

Recommendations

When planting a newly capped landfill, use native warm-season grasses or native grass/wildflower mixes available from nurseries. (See Table 2, Native Grasses/Sedges Recommended for Grassland Bird Habitat and Table 3, Nurseries Specializing in Native Grasses and/or Wildflowers for list of grasses and supplying nurseries.)

Mowing is necessary at capped landfills to prevent growth of woody vegetation. Plan to mow after August 1 to allow grassland birds to nest and fledge their young. If possible, delay mowing to every one to three years. This will reduce maintenance costs and create better habitat for grassland birds.

Protect wetlands surrounding landfills with a buffer of natural vegetation. See "Wetlands protection" below for specific information on buffer size.

Education can enhance a capped landfill to provide for both wildlife habitat and public recreation. Educational displays can show birds, butterflies, and mammals that may be observed at these sites. Displays can illustrate how a landfill becomes wildlife habitat. Provide observation areas to increase public awareness and appreciation of these interesting habitats. Protect known nesting areas from human disturbance during the breeding season by placing "Grassland Bird Nesting Area" signs in the grasslands and by providing clearly identified mowed paths along field edges for public use.

Grassland Restoration

Areas that have been neglected, invaded with woody vegetation, overgrazed, or planted with alfalfa or row crops can be restored into grasslands that will provide habitat for grassland birds.

Size: Grassland restoration aimed at attracting area-sensitive grassland birds should be at least 125 acres and preferably larger than 250 acres.

Protection from overgrazing: Follow the previous guidelines under "Mowing" and "Grazing" to restore a grassland to a more natural and diverse system and to provide improved habitat for grassland birds.

Grassland design: Plant grassland planting to minimize the amount of edge. Square plots are preferred to long rectangular plots or plots with irregular borders. This will maximize the amount of interior habitat available and minimize nest predation, which is most frequent along edges.

Edge habitat: Preferably, land adjacent to areas being restored should be open and not bordered by tall fence lines or trees. Open pastures, hayfields, grain fields, row crops, and grassed waterways are ideal adjacent habitat.

Wetlands protection: Wetlands adjacent to fields are especially important for wildlife habitat, and surrounding buffers aid in the breakdown of pollutants from agricultural runoff. Runoff includes nutrients in fertilizers and harmful bacteria and viruses in manure. The wider the buffer of natural vegetation, the greater will be the reduction of pollutants. In fields that are in agricultural use, and where cultivation already occurs close to a wetland, a buffer zone of 20 feet provides some water quality benefits. However, a buffer of 60 feet or more will make a greater contribution to controlling pollutants and should be the minimum wherever possible.

For maintaining good wildlife habitat in a wetland, as well as controlling pollutants, a buffer of 300 feet is preferable. Decisions of buffer size will depend on the type and degree of pollution, slope, soil type, vegetation, and value of the wetland as wildlife habitat.

Removal of woody vegetation: Woody vegetation can be removed along field edges, particularly those dividing fields, and in grasslands that have become overgrown with woody vegetation. This will help create the look of a larger grassland, ideal for area-sensitive species. Removal of woody vegetation can be achieved by a variety of means: mechanically, chemically, or by burning. Removal should be avoided during the nesting season to minimize disturbance to nesting birds. These areas can be burned and/or cut to restore grass dominance. An intensive spring fire regime for several years will help kill shrubs and encourage growth of native species. Once shrub growth is retarded, burning can be reduced to a light burn every two to six years to maintain grasses. Cutting and burning may be necessary in areas invaded by stubborn woody plants. Spot treatment is often used to help remove particularly stubborn shrubs and trees. Some herbicides may be applied directly to the newly cut shrub stems. Read herbicide labels carefully and consult your local Cooperative Extension Service office regarding use of herbicides (see Table 4, Agencies or Organizations Specializing in Agricultural Land Management Issues).

Replanting with warm-season grasses: Areas void of vegetation should be disked and plowed in the fall, and disked again in the spring and seeded with native warm-season grasses. Attention should be paid to soil type, moisture content, slope, and site preparation to successfully seed a grassland. Providing firmly packed soil and a weed-free seedbed is necessary to successfully seed a field. After substantial growth, periodic rejuvenation, such as burning, will maintain a healthy stand of grass. Consult soils maps, available from state Natural Resources Conservation Service offices (see Table 4, Agencies or Organizations Specializing in Agricultural Land Management Issues), to determine what types of grasses will grow best on your soil type. (See Table 3, Nurseries Specializing in Native Grasses and/or Wildflowers for a list of nurseries specializing in native grass seeds.) Include native wildflowers in grass seed mixture if possible to create a more diverse grassland and provide food and habitat for other songbirds and butterflies.

Use of pesticides: If you are restoring a site formerly in crop production, attention should be paid to former use of pesticides and herbicides. If cropland was recently treated with certain chemicals, planted grasses may not grow. Consult your local Natural Resources Conservation Service office (see Table 4, Agencies or Organizations Specializing in Agricultural Land Management Issues) to determine the best way to proceed.

Planting fields in warm-season grasses, in addition to the more commonly planted cool-season grasses, can benefit both the farmer and wildlife. The differences between the two grass types are described in Table 5, Warm Season vs. Cool Season Grasses.