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Effects of Management Practices on Grassland Birds:

American Bittern

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and effects of habitat management on grassland birds were summarized from information in more than 5,500 published and unpublished papers.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 American Bittern 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 include protecting wetlands and adjacent uplands and maintaining idle upland habitat.

Breeding Range:

Suitable habitat:

Within wetlands and wet meadows, American Bitterns nest in rush (Juncus), sedge (Carex spp.), bulrush (Schoenoplectus spp.), prairie cordgrass (Spartina pectinata), sprangletop (Scolochloa festucacea), tall mannagrass (Glyceria grandis), common reed (Phragmites australis), reed canary grass (Phalaris arundinacea), bur-reed (Sparganium eurycarpum), or cattail (Typha) (Gabrielson 1914, Lewis 1930, Mousley 1939, Vesall 1940, Provost 1947, Middleton 1949, Boyer and Devitt 1961, Bent 1963, Stewart 1975, Duebbert and Lokemoen 1977, Faanes 1981, Manci and Rusch 1988, Brininger 1996, Azure 1998). Bitterns nest on floating platforms in shallow (3-91 cm) water (Provost 1947, Middleton 1949, Bent 1963, Stewart 1975, Brininger 1996). The average vegetation height above water within 1-10 m of wetland nests in northwestern Minnesota was 126 cm (Brininger 1996). Water depths within 1-10 m of wetland nests ranged from 8 to 65 cm (Brininger 1996, Azure 1998). Territories in Minnesota were characterized by average values of 10 cm water depth, 1.4 m vegetation height, 8.7% vegetation cover, 114 stems/m² grass density, and 4 stems/m² forb density (Hanowski and Niemi 1986). Two nests in a Minnesota wet meadow were located 61 m and 107 m from water (Vesall 1940). In northwestern Iowa, American Bitterns nested in 2- and 4-yr-old restored wetlands (VanRees-Siewert 1993, VanRees-Siewert and Dinsmore 1996). A significant positive relationship was found between the age of restored wetlands and the occurrence of American Bitterns.

Within uplands, American Bitterns nest in both grassland and shrubland (Duebbert and Lokemoen 1977, Knapton 1979, Kantrud and Higgins 1992, Svedarsky 1992). In Manitoba, Montana, North Dakota, and South Dakota, American Bitterns nested in mid to tall (30-99 cm), dense, idle grasslands where the average maximum height of the leaf canopy (effective vegetation height) was >60 cm, 100% vertical visual obstruction was usually >50 cm, and litter cover was >50% (Kantrud and Higgins 1992). They avoided nesting in areas where vegetation height or 100% vertical visual obstruction values were <30 cm or where the total cover contained >10% dead vegetation. Dominant plant species around nests were smooth brome (Bromus inermis), wheatgrass (Agropyron), alfalfa (Medicago sativa), and big bluestem (Andropogon gerardii) (Duebbert and Lokemoen 1977, Kantrud and Higgins 1992). Nests were partially or completely concealed by vegetation on the side, but partially or completely exposed on top, and no nests were found in cover <30 cm tall (Duebbert and Lokemoen 1977). Dominant plant species around grassland nests in northwestern Minnesota were smooth brome, reed canary grass, timothy (Phleum pratense), redtop (Agrostis stolonifera), quackgrass (Agropyron repens), switchgrass (Panicum virgatum), sweet clover (Melilotus spp.), and big bluestem (Svedarsky 1992, Brininger 1996, Azure 1998). Average vegetation height within 1-10 m of grassland nests was about 73 cm (Brininger 1996). Average vertical visual obstruction values of vegetation ranged from 44 to 99 cm around nests in North Dakota and Minnesota (Messmer 1985, Svedarsky 1992, Azure 1998). Nests were located in tall (>60 cm) vegetation (Svedarsky 1992). An American Bittern nested successfully in an interstate road right-of-way in southcentral North Dakota (Oetting and Cassel 1971). In Saskatchewan, nests were located in hayfields and dense western snowberry (Symphoricarpos occidentalis) 80-100 m from water (Knapton 1979). In Manitoba, adult behaviors indicative of breeding (territorial male present, breeding pair present, nest building activity, egg laying, egg incubation, or distraction display) were recorded in native grassland and hayland, but not in cropland or woodland (Jones 1994).

During molt, American Bitterns move away from their breeding territories to isolated areas, such as islands (Brininger 1996). Azure (1998) documented American Bitterns molting in dense stands of cattail. A table near the end of the account lists the specific habitat characteristics for American Bitterns by study.

Area requirements:

Brown-headed Cowbird brood parasitism:

Breeding-season phenology and site fidelity:

Species' response to management:

Management Recommendations:

Protect wetlands from drainage through conservation easements, land purchases, tax incentives, management agreements, continuation of the Wetland Reserve Program, and enforcement of wetland-protection regulations (Brown and Dinsmore 1986, Hands et al. 1989, Gibbs et al. 1992, Daub 1993).

Maintain a complex of wetlands of sufficient size (wetlands 20-30 ha in size up to 180 ha) to provide habitats at various stages of succession (Brown and Dinsmore 1986, Hands et al. 1989). American Bitterns occurred in wetlands ranging in size from 3 to 182 ha (Brown and Dinsmore 1986, Daub 1993).

Protect wetlands from siltation, eutrophication, chemical contamination, and other forms of pollution (Gibbs et al. 1992).

Maintain water levels at <61 cm throughout the breeding season (April-August) (Hands et al. 1989, Azure 1998). Avoid complete drawdowns before mid-August (Azure 1998). During molting, bitterns need relatively deep, stable waters to provide adequate food and protection from predators (Azure 1998). Use slow drawdowns to mimic natural wetland succession (Fredrickson and Reid 1986).

If stock ponds are a part of a management plan, manage for growth of emergent vegetation (Weber 1978). In South Dakota, American Bitterns most often were located in semipermanent wetlands or wetlands with open water in the center, a band of emergent vegetation around the periphery, and idle grassland in the adjacent uplands (Weber 1978, Weber et al. 1982).

Maintain a wide vegetative margin around wetlands to protect breeding habitat and to deter nest predators (Daub 1993).

To maintain tall, dense, upland vegetation, disturbance (e.g., mowing, burning, and grazing) should not occur more often than every 2-5 yr (Duebbert and Lokemoen 1977).

Although American Bitterns nested only in idle grasslands, the twice-over deferred rotation grazing system may be the best grazing system in terms of providing overall bird nesting cover in uplands (Messmer 1985). Encourage adoption of no-tillage or minimum-tillage practices instead of conventional-tillage (annual) practices, so that breeding habitat is undisturbed during the nesting season (Kantrud and Higgins 1992).

Table.  American Bittern 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