Incorporating landscape attributes into models for migratory grassland bird conservation

摘要

We evaluated the influence of local and landscape attributes on the occurrence and density of seven passerine species in grasslands (n = 380) throughout eastern South Dakota ( U. S. A.). Landscape composition and land cover were quantified at three spatial scales: 400-, 800-, and 1600- m radii from the transect center. Separate habitat models were generated for mixed-grass and tallgrass prairie regions to depict the way birds respond to geographic variation in local and landscape structure. Sedge Wrens ( Cistothorus platensis) and Clay-colored Sparrows ( Spizella pallida) in the mixed-grass and tallgrass regions used both large and small patches if they were embedded in a landscape with a high proportion of grassland habitat. Occupancy rates for these species were higher in small patches within landscapes with high grassland abundance than in large patches within low grassland landscapes. Grasshopper Sparrows ( Ammodramus savannarum) and Dick-cissels ( Spiza americana) in the mixed-grass region and Savannah Sparrows ( Passerculus sandwichensis) in the tallgrass region were area-sensitive species that used large grassland patches regardless of landscape configuration. The occurrence of Savannah Sparrows in both regions and Sedge Wrens, Grasshopper Sparrows, and Western Meadowlarks (Sturnella neglecta) in the mixed-grass region was negatively associated with an increase in patch edges with trees. Explained variation in density estimates was associated only with local patch and vegetation variables. Individual species demonstrated scale-dependent differences in the way they perceived habitat and in their response to regional landscape structure. These findings provide evidence that results from one region may not be extrapolated to others because they may vary with species distribution, vegetation structure, and landscape composition. Assessments of regional grassland bird habitat must be conducted at multiple scales because some species respond only to local conditions within grasslands, whereas others respond to habitat structure at landscape scales. [References: 33]