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Effects of Management Practices on Grassland Birds:

Bobolink

This resource is based on the following source:

  View the PDF version of this Species Account  (requires a PDF Reader, download free reader)

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Organization and Features of this Species Account

Information on the habitat requirements and effects of habitat management on grassland birds were summarized from information in more than 5,500 published and unpublished papers. A range map is provided to indicate the relative densities of the species in North America, based on Breeding Bird Survey (BBS) data. Although birds frequently are observed outside the breeding range indicated, the maps are intended to show areas where managers might concentrate their attention. It may be ineffectual to manage habitat at a site for a species that rarely occurs in an area. The species account begins with a brief capsule statement, which provides the fundamental components or keys to management for the species. A section on breeding range outlines the current breeding distribution of the species in North America, including areas that could not be mapped using BBS data. The suitable habitat section describes the breeding habitat and occasionally microhabitat characteristics of the species, especially those habitats that occur in the Great Plains. Details on habitat and microhabitat requirements often provide clues to how a species will respond to a particular management practice. A table near the end of the account complements the section on suitable habitat, and lists the specific habitat characteristics for the species by individual studies. A special section on prey habitat is included for those predatory species that have more specific prey requirements. The area requirements section provides details on territory and home range sizes, minimum area requirements, and the effects of patch size, edges, and other landscape and habitat features on abundance and productivity. It may be futile to manage a small block of suitable habitat for a species that has minimum area requirements that are larger than the area being managed. The Brown-headed Cowbird (Molothrus ater) is an obligate brood parasite of many grassland birds. The section on cowbird brood parasitism summarizes rates of cowbird parasitism, host responses to parasitism, and factors that influence parasitism, such as nest concealment and host density. The impact of management depends, in part, upon a species' nesting phenology and biology. The section on breeding-season phenology and site fidelity includes details on spring arrival and fall departure for migratory populations in the Great Plains, peak breeding periods, the tendency to renest after nest failure or success, and the propensity to return to a previous breeding site. The duration and timing of breeding varies among regions and years. Species' response to management summarizes the current knowledge and major findings in the literature on the effects of different management practices on the species. The section on management recommendations complements the previous section and summarizes specific recommendations for habitat management provided in the literature. If management recommendations differ in different portions of the species' breeding range, recommendations are given separately by region. The literature cited contains references to published and unpublished literature on the management effects and habitat requirements of the species. This section is not meant to be a complete bibliography; for a searchable, annotated bibliography of published and unpublished papers dealing with habitat needs of grassland birds and their responses to habitat management, use the Grassland and Wetland Birds Bibliography on the home page of this resource.

This report has been downloaded from the Northern Prairie Wildlife Research Center World-Wide Web site, http://www.npwrc.usgs.gov/resource/literatr/grasbird/. Please direct comments and suggestions to Douglas H. Johnson, Northern Prairie Wildlife Research Center, U.S. Geological Survey, 8711 37th Street SE, Jamestown, North Dakota 58401; telephone: 701-253-5539; fax: 701-253-5553; e-mail: Douglas_H_Johnson@usgs.gov.

Figure.  Breeding distribution of the Bobolink in the United States and southern Canada, based on Breeding Bird Survey data, 1985-1991. Scale represents average number of individuals detected per route per year. Map from Price, J., S. Droege, and A. Price. 1995. The summer atlas of North American birds. Academic Press, London, England. 364 pages.

Keys to management are providing large areas of suitable habitat (native and tame grasslands of moderate height and density, with adequate litter), controlling succession, and protecting nesting habitat from disturbance during the breeding season.

Breeding Range:

Suitable habitat:

In Nebraska, Bobolinks nested in wet prairie, alfalfa, upland native prairie, domestic hayland, and wheat (Faanes and Lingle 1995). Bobolinks in Iowa nested under or near native bluestem (Andropogon or Schizachyrium not specified) or Kentucky bluegrass (Kendeigh 1941). Bobolinks in Wisconsin nested at the bases of large forbs (Martin 1971). In Montana, Bobolinks nested in a wet-meadow pasture (Silloway 1904). In Ontario, Bobolinks nested in a weedy meadow near a wetland; nests were built in the litter layer, had a canopy of dead grasses, and were surrounded by living vegetation 33-41 cm tall (Boyer and Devitt 1961, Joyner 1978). Bobolinks have been found nesting in CRP fields in Iowa and Michigan (Best et al. 1997).

Bobolinks occasionally nest in cropland. In Iowa, Bobolinks nested at low densities in untilled fields of corn that were idle in the fall and spring and contained year-round crop residue, rather than in tilled fields or strip cover (Basore et al. 1986). In Wisconsin, a few Bobolinks were found in small-grain fields, but none were found in rowcrops (Sample 1989). The species was absent from cropland in Saskatchewan and Manitoba (Hartley 1994, Jones 1994). A table near the end of the account lists the specific habitat characteristics for Bobolinks by study.

Area requirements:

In Minnesota tallgrass prairie, nest depredation and Brown-headed Cowbird (Molothrus ater) brood parasitism decreased farther from woody edges, and nest depredation rates were lower on large (130-486 ha) than on small (16-32 ha) grasslands (Johnson and Temple 1990). Nest productivity in Minnesota was highest for nests in habitats far (>45 m) from a forest edge (Johnson and Temple 1986). In Nebraska, Bobolink abundance was lower near woody edges (<100 m) than far (>100 m) from woody edges (Helzer 1996). In Colorado, Bock et al. (1999) compared the abundance of Bobolinks between interior and edge locations. Edge was defined as the interface between suburban development and upland or lowland habitat, and interior locations were 200 m from edge. Bobolinks were significantly more abundant on interior plots than on edge plots.

Brown-headed Cowbird brood parasitism:

Breeding-season phenology and site fidelity:

Species' response to management:

In Nebraska, Bobolinks occurred more frequently in tallgrass hayland than tallgrass pasture (Helzer 1996). In North Dakota, Kantrud (1981) found the highest Bobolink densities in hayland mowed the previous year, with lightly grazed areas containing the second highest densities. In another North Dakota study, there was no difference in abundance in the year following haying between hayed and idled portions of CRP fields (Horn and Koford 2000). In Michigan and Wisconsin, Bobolinks were common in hayfields before mowing, but deserted these fields after the fields were mowed (Harrison 1974, Sample 1989). In Missouri, however, Skinner (1974) found that Bobolinks were present in hayfields before and after mowing. In Illinois, a decline in Bobolink abundance was significantly correlated with declines in the number of hectares of alfalfa, oats, and pasture in the northern one-third of the state from 1952 to 1992 (Herkert 1997). In Saskatchewan, Bobolinks were more abundant in emergency-mowed (mowed during drought years) tame hayfields than in native grassland, tame grassland, or annually mowed tame haylands (Dale 1992). Dale et al. (1997) found that Bobolink abundance in Saskatchewan was higher in annually or periodically (idle for 4-8 yr) mowed tame hayland than in idle native grassland. However, mowing during the breeding season can cause high rates of nest failure for Bobolinks; mowing accounted for 51% of Bobolink nest losses in a New York hayfield (Bollinger et al. 1990).

In the Great Plains, measures of abundance indicated that Bobolinks responded positively to moderate grazing in tallgrass, but negatively to heavy grazing in shortgrass (Bock et al. 1993). In southeastern North Dakota, Bobolinks occurred in grazed areas that had few shrubs and moderate to deep litter (Messmer 1990). Higher densities of Bobolinks were found in areas under a short-duration grazing treatment (involved a system of pastures rotated through a grazing schedule of about 1 wk grazed and 1 mo ungrazed) than in idle areas. In southwestern Wisconsin, Bobolinks were nearly equally abundant in rotationally grazed pastures, continuously grazed pastures, and ungrazed pastures (Temple et al. 1999). Ungrazed grasslands were neither mowed or grazed from 15 May to 1 July. Continuously grazed sites were grazed throughout the summer at levels of 2.5-4 animals/ha. Rotationally grazed pastures, stocked with 40-60 animals/ha, were grazed for 1-2 d and then left undisturbed for 10-15 d before being grazed again; pastures averaged 5 ha. All sites were composed of 50-75% cool-season grasses, 7-27% legumes, and 8-23% forbs. In southeastern South Dakota, Bobolinks preferred lightly grazed areas on typic ustoll soils (Kantrud and Kologiski 1982). In Missouri, Bobolinks were most abundant in lightly to moderately grazed tallgrass prairie and were not present in idle prairie (Skinner 1974, 1975). In Alberta, Bobolinks were found in tame pastures but not in native pastures (Prescott and Murphy 1996).

Bobolinks nested or were found in CRP fields in Iowa, Michigan, Minnesota, Montana, Nebraska, North Dakota, and South Dakota (Johnson and Schwartz 1993, Patterson and Best 1996, Best et al. 1997, Delisle and Savidge 1997). In North Dakota, higher densities of Bobolinks were found in DNC planted to alfalfa and wheatgrass (Agropyron spp.) than in idle mixed-grass prairie (Renken 1983, Renken and Dinsmore 1987). In CRP fields in Nebraska, Bobolink abundance was significantly higher in cool-season grasses than in warm-season grasses, possibly because of shorter vegetation in cool-season grasses (Delisle and Savidge 1997). King and Savidge (1995) found Bobolinks in tallgrass prairie and CRP planted to cool-season grasses but did not find them in CRP planted to warm-season grasses. In Minnesota and North Dakota, Koford (1999) reported that Bobolink abundance was equal or nearly equal between CRP fields and Waterfowl Production Areas (tracts of grassland and wetland managed by the U. S. Fish and Wildlife Service to provide nesting and brood-rearing habitat for waterfowl). In Manitoba and Saskatchewan, Bobolinks were found in native and tame DNC and in idle native grassland (Dhol et al. 1994, Hartley 1994); wheat fields were avoided (Hartley 1994). Bobolinks also were found in Permanent Cover Program lands in Canada (McMaster and Davis 1998). PCP was a Canadian program that paid farmers to seed highly erodible land to perennial grassland cover; it differed from CRP in the United States in that haying and grazing were allowed annually in PCP. In Canadian aspen parkland, Bobolinks occurred more frequently in PCP than in cropland (McMaster and Davis 1998). However, their frequency of occurrence did not differ between hay and pasture sites within the parkland PCP sites. In North Dakota, Bobolinks were present in areas seeded to native grasses 1 yr after seeding occurred (Higgins et al. 1984). In Wisconsin, Bobolinks occurred in a restored native tallgrass prairie site 3 yr following seeding (Volkert 1992).

In Maine, territory density of Bobolinks decreased for 2-5 yr following the application of the herbicide hexazinone at a rate of 4 kg/ha on lowbush blueberries (Vaccinium angustifolium) (Vickery 1993).

Management Recommendations:

Regardless of geographic location, avoid disturbing (e.g., haying, burning, moderately or heavily grazing) nesting habitat during the breeding season, approximately early May to mid-July (Bollinger 1991). Treatments can be done in early spring (several weeks prior to the arrival of adults on the breeding grounds) or in the fall after the breeding season (Martin and Gavin 1995). Recommendations follow for the Great Plains and for the East and Midwest.

Great Plains (based on studies from Nebraska, North Dakota, South Dakota, and Saskatchewan):

Create large patches of habitat and minimize woody edges whenever possible to increase Bobolink densities (Johnson and Temple 1990, Helzer 1996, O'Leary and Nyberg 2000). In Nebraska, minimum patch size requirement for wet meadows was >40 ha, and Bobolink abundance was lower near woody edges (<100 m) than far (>100 m) from woody edges (Helzer 1996). Shape, as well as area, of management units must be taken into consideration; perimeter-area ratio strongly influenced occurrence of Bobolinks in Nebraska (Helzer and Jelinski 1999).

Reduce amount of grassland edge near suburban interfaces (Bock et al. 1999).

Burn habitat once every 2-4 yr to prevent encroachment of woody vegetation and remove deep litter (Johnson and Temple 1990, Madden 1996, Johnson 1997, Madden et al. 1999).

Conduct controlled burns on CRP fields every 3-5 yr to reduce dense vegetation (King and Savidge 1995). In Nebraska, Bobolink abundance was negatively correlated with vertical density of vegetation (Delisle and Savidge 1997).

Burn large areas on a rotational basis, burning portions of the total area each year (Johnson 1997). Burn small areas periodically. Ensure that adjacent areas are burned in different years to create a variety of successional stages.

Provide hayland areas, and mow as late as possible. In Nebraska, Bobolinks occurred more frequently in native hayland than pastures (Helzer 1996). Kantrud (1981) found Bobolink densities to be highest in hayland mowed the previous year, with lightly grazed areas containing the second highest density. Dale et al. (1997) found that Bobolink abundance in Saskatchewan was higher in annually or periodically mowed tame hayland than in native grassland.

Delay mowing until after 15 July, by which time at least 70% of nestlings will have fledged in years of normal breeding phenology (Dale et al. 1997). To maintain dense cover in idle haylands, mow some fields in alternate years while leaving others idle for at least 3 yr. Divide large fields in half, with each half being mowed in alternate years, thus ensuring productivity of hay and of birds.

Lightly graze areas where Bobolinks have exhibited positive responses to this treatment; heavy or moderate grazing may negatively affect Bobolink populations (Kantrud 1981).

East and Midwest (based on studies from Illinois, Iowa, Michigan, Minnesota, Missouri, New York, and Wisconsin):

Delay treatments until late July or August to protect fledglings and late-nesting females (Bollinger 1991). Mowing accounted for 51% of Bobolink nest losses in a New York hayfield (Bollinger et al. 1990).

Create large habitat patches (>10-30 ha) and minimize woody edges whenever possible to decrease Brown-headed Cowbird brood parasitism (Bollinger and Gavin 1992).

Use a rotating treatment schedule on several nearby prairie fragments to make a variety of successional stages available (Herkert 1994b). Adjacent patches of alternative habitat provide refuge for fledglings to escape from mowed areas and for late-nesting females (Bollinger et al. 1990).

Create or maintain patches of relatively sparse, grass-dominated vegetation resembling old (>8 yr since planted) hayfields (Bollinger and Gavin 1992). Scattered forbs (e.g., clover [Trifolium spp.]) should be encouraged for nest-site cover. Bollinger (1988, 1995) found that a minimal forb component for nesting cover was beneficial, but Bobolinks preferred haylands with high grass-to-forb ratios and avoided haylands with high legume-to-grass ratios.

Burn large areas (>80 ha) using a rotational system. Subunits of ≥30 ha in area, or about 20-30% of the total area, should be treated in a year (Herkert 1994b). Johnson and Temple (1990) found lower rates of nest depredation on Bobolink nests in recently burned (≤3yr) areas in Minnesota.

In small, isolated prairie fragments, burn ≤50-60% of the total area at a time (Herkert 1994b).

Mow or burn patches every 2-3 yr to prevent excessive encroachment of woody vegetation (Bollinger and Gavin 1992, Herkert 1994a). In most years, delaying mowing until the end of June may allow young Bobolinks time to fledge (Harrison 1974).

Graze at moderate levels to provide diverse grass heights and densities in areas where the average height of vegetation is 20-30 cm (Skinner 1974, 1975). Graze using a rotational system of two or more grazing units (Skinner 1974). This will increase the variation in grass heights and densities within and between units. To maintain plant vigor, do not graze warm-season grasses in tallgrass prairie to a height of <25 cm during the growing season (Skinner 1975).

Table.  Bobolink habitat characteristics.

* In an effort to standardize terminology among studies, various descriptors were used to denote the management or type of habitat. "Idle" used as a modifier (e.g., idle tallgrass) denotes undisturbed or unmanaged (e.g., not burned, mowed, or grazed) areas. "Idle" by itself denotes unmanaged areas in which the plant species were not mentioned. Examples of "idle" habitats include weedy or fallow areas (e.g., oldfields), fencerows, grassed waterways, terraces, ditches, and road rights-of-way. "Tame" denotes introduced plant species (e.g., smooth brome [Bromus inermis]) that are not native to North American prairies. "Hayland" refers to any habitat that was mowed, regardless of whether the resulting cut vegetation was removed. "Burned" includes habitats that were burned intentionally or accidentally or those burned by natural forces (e.g., lightning). In situations where there are two or more descriptors (e.g., idle tame hayland), the first descriptor modifies the following descriptors. For example, idle tame hayland is habitat that is usually mowed annually but happened to be undisturbed during the year of the study.

Literature Cited