| Conservation Planning
and Monitoring Avian Habitat Daniel J. Twedt 1 and Charles R. Loesch 2
INTRODUCTION Arresting declining populations of Neotropical migratory birds will, in many cases, require migratory bird conservation plans that include regional and local management actions. Bird conservation plans developed for physiographic areas or smaller local areas will likely focus on maintaining or increasing populations of specific bird species (Mueller et al, this volume). Progress toward population goals set by these bird conservation plans, however, will be difficult to evaluate. In some cases, established population goals, especially those for migratory birds, may be unreachable by actions undertaken solely within the geographic boundaries covered by the conservation plan. For example, factors outside established boundaries may adversely impact some species. Even when population goals can be attained by conservation efforts within defined geographic boundaries, assessing progress toward population goals may be difficult. Monitoring bird populations and their demographics over large geographic areas and over extended time periods can be a Herculean task in terms of personnel and financial resources (Sherry and Holmes, this volume). Fortunately, many species of concern to managers are closely linked to specific habitat types (Hamel 1992, Hunter et al. 1993). Often, behavioral and spatial relationships exist which allow quantifiable breeding bird populations to be associated with specified areas of designated habitat types. We recommend that bird conservation plans establish habitat objectives that enhance the likelihood of achieving avian population goals. To be effective, habitat objectives must be achievable regardless of external impacts on bird populations. Once established, habitat objectives provide benchmarks that usually can be measured, evaluated, and achieved more easily than population goals. DETERMINING BASELINE HABITAT DATA After habitats critical to migratory bird species of concern within a planning unit have been identified, the availability of these habitats should be assessed. At landscape scales, this assessment can be achieved through remote sensing technologies such as satellite imagery. Remotely sensed data can be obtained at scales from 1 km to less than 10 m using panchromatic, multispectral, infrared, or radar sensors. Choice of scale and sensor often are dictated by cost and the extent and location of desired coverage. Planners should consult with experts in remote sensing or geographic information systems (GIS) to ascertain the advantages of different imaging systems. Managers planning at local scales have additional options for assessing avian habitats, including aerial photography and videography. When available, archived and current management records might provide accurate and detailed descriptions of habitats. Finally, ground reconnaissance should be used to delineate habitats or to verify habitat assessments from other sources. Whether at landscape or local scales, information about avian habitats must be organized in a format that is conducive to planning and ultimately to monitoring. A GIS format is appropriate because remotely sensed data are available in digital form and can be imported directly . Additionally, these digital data must represent habitat types that are derived via computerized classification procedures. Other habitat data, such as photographs, management records, and ground reconnaissance, can be entered into a GIS by scanning or by digitizing maps. For example, in the Mississippi Alluvial Valley, the extent and distribution of bottomland hardwood forest (critical habitat for avian species of concern in the Mississippi Valley [Mueller et al, this volume]) were classified from Thematic Mapper imagery (Fig. 1). We suggest using this type of data on avian habitats as baseline data from which to establish habitat objectives. In many states, digital habitat data derived from Thematic Mapper imagery are currently or soon will be available for wildlife conservation planning through statewide “Gap analysis” projects (Scott et al. 1993). Figure 1. Distribution of forested habitat within the Mississippi “Delta,” that portion of the Mississippi Alluvial Valley between Vicksburg, Mississippi, and Memphis, Tennessee, circa 1992, circa 1976, and circa 1957.
ESTABLISHING HABITAT OBJECTIVES The area and distribution of habitat objectives can be established from a direct assessment of hypothesized habitat needs (Mueller et al. this volume) or indirectly based on the needs of previously identified population goals (Loesch et al. 1994, Loesch et al. this volume). Regardless of how established, habitat objectives can be categorized as: maintaining existing habitats, restoring former habitats, or creating new or alternative habitats. All categories should be considered when formulating habitat objectives. For example, to ensure continuation of extant habitats, management plans may suggest maintaining current habitat conditions (e.g., uneven-aged timber harvest) or they may compensate for habitat change by replacing existing habitat with habitat at other sites (e.g., even-aged, rotational timber harvest). Even maintaining existing habitats may be a significant challenge in areas where urban encroachment is fragmenting existing avian habitats. Before restoring habitat, examining the historical distribution of habitats is useful. Although remotely sensed data are available for only about the past 30 years, cartographic data may be obtained for much earlier periods. Historical land surveys, topographic maps, or aerial photographs might reveal dramatic changes in avian habitats compared to current conditions. When conservation plans include restoring former habitats, historical information can be an important guide to developing logical and achievable restoration objectives. Other factors also may indicate where restoring habitat is practical. For example, soil type often determines what plant communities will thrive, thereby defining avian habitats. Similarly, water-control projects (i.e., dams and levees) have altered the hydrology of many ecosystems to the extent that restoration of historical habitats is not feasible. Thus, inclusion of soil type and hydrologic data in a GIS will provide important ancillary information for identifying areas for habitat restoration. In areas where maintaining and restoring endemic avian habitat are not feasible, creating new habitat, establishing alternative habitat, or implementing management practices that promote avian use of existing habitats may be practical solutions. For example, in the Mississippi Alluvial Valley, replacing conventional row crops with short-rotation agroforestry provides breeding, migration, and wintering habitat for migratory forest birds while continuing to provide income for landowners. Another alternative incorporates water-control structures within existing agricultural fields to retain water on harvested croplands, thereby providing foraging habitat for wintering waterfowl without restricting farm operations during the growing season. MONITORING PROGRESS TOWARD HABITAT OBJECTIVES After habitat objectives have been established, data added to the GIS will aid in monitoring progress toward these objectives. On a landscape scale, for example, the areas of public land ownership (e.g., National Wildlife Refuges, State Wildlife Management Areas, National Forests, State Parks, etc.) and management (e.g., natural areas, wildlife management, multipurpose management, etc.) can be incorporated into the GIS (Fig 2). Similarly, private lands enrolled in conservation easements (e.g., Ducks Unlimited), in government programs (e.g., Conservation Reserve or Wetland Reserve), or maintained for long-term economic return (e.g., corporate timber holdings and private grazing land) can be added to the GIS (Fig 3). The area and location of these dedicated conservation lands, in relation to habitat objectives, directly affects our ability to maintain existing avian habitats. Additionally, these lands provide opportunities to restore former habitats and can serve as areas to focus habitat restoration. Figure 2. Location of
public lands within the Mississippi “Delta,” that portion of the Mississippi
Alluvial Valley between Vicksburg, Mississippi, and Memphis, Tennessee.
Projects to restore habitats often are part of larger conservation efforts; therefore managers should ensure that the areas influenced by their restoration project are accurately delineated on georeferenced maps or geocoded (e.g., by global positioning systems). When private landowners restore habitat, they should be encouraged or assisted in geocoding the area impacted, and these data should be incorporated into the habitat-monitoring database. When alternate land management or conservation enhancements are developed, such as installation of water-control structures, the lands affected should also be incorporated into the GIS (Fig. 3). Figure 3. Lands enrolled
in the Wetland Reserve Program and private lands under cooperative agreements (e.g.,
Mississippi Partners projects) to manage wildlife within the Mississippi
“Delta,” that portion of the Mississippi Alluvial Valley between Vicksburg,
Mississippi, and Memphis, Tennessee.
On a local scale, similar data can be incorporated into migratory bird conservation plans for wildlife management areas or other management units (Fig. 4). Habitat objectives within the management unit can be established in concert with habitat objectives set at a landscape scale and restored or modified habitat can be added to the GIS (Fig. 5). Figure 4. Four forest classes derived from 1992 Thematic Mapper imagery of the northern portion of Tensas River National Wildlife Refuge, Louisiana. Black line depicts refuge boundary.
Figure 5. Areas of reforestation, areas of timber harvest, and areas of unmanaged forest on the northern portion of Tensas River National Wildlife Refuge, Louisiana.
Identification of public and private managed lands, inclusion of restoration areas, and identification of areas under alternative management may be sufficient to monitor progress toward achieving migratory bird habitat objectives at local scales. However, to monitor progress toward habitat objectives at landscape scales, we recommend using remote sensing to periodically update habitat data. ACKNOWLEDGMENTS We thank S. E. Mott, C. K. Baxter, and K. J. Reinecke for stimulating discussions in formulating this paper. J. Sauer, B. Varin, and D. Rassa provided editorial reviews. LITERATURE CITED
1 USGS
Patuxent Wildlife Research Center 2 Habitat and Population Team |
