An evaluation of habitat use and requirements for grassland bird species of greatest conservation need in central and western South Dakota

Tall and mixed-grass prairies are being urbanized or converted to cropland at an accelerated rate. Nationwide, these losses total 99.9% for tall-grass and 70-80% for mixed-grass prairies. Previous research has shown that local vegetation structure affects habitat use by grassland birds. In addition, patch size and landscape composition affect the presence, density, and nesting success of some, but not all, grassland obligate bird species. Current trends in grassland conversion, fragmentation due to these conversions and man-made shelterbelts and degradation by exotic plant species have made grassland birds one of the fastest declining guilds in North America. Little research has been conducted on grassland birds of the mixed-grass prairie, and for many of these species, South Dakota constitutes area of highest abundance or the central portion of their breeding range.;Objectives of this study were to identify: (1) local habitat characteristics, (2) habitat associations, and (3) patch and landscape level habitat requirements for grassland birds in the mixed-grass prairies of South Dakota. These objectives evaluated and determined the distribution and habitat use as related to historical ecosystem diversity for grassland birds of the mixed-grass prairie in South Dakota.;I used fixed-width belt transects to survey birds on 288 native sod sites in 29 counties within central and western South Dakota during the breeding seasons of 2007 and 2008. Vegetation structure and composition were surveyed at 50m increments along each bird survey transect. Arc-GIS, aerial photographs, and the National Land Cover Database (2001) were used to calculate grassland patch size, amount of woody edge and amount of grassland habitat within concentric buffers (400m, 800m, 1600m and 3200m) around the survey points.;Grasshopper sparrows (N=203) were the most common bird detected within our transects. Of the study species, Chestnut-collared longspurs had the highest male density (124 males/100ha) followed by the grasshopper sparrow (107males/100ha). I found that occurrence and density of grassland obligate bird species were influenced by numerous habitat characteristics and at multiple scales. These models showed a large variation in local vegetation characteristics being selected for by grassland bird species. Increasing coverage of grasslands by exotic plant species had a negative effect on four (chestnut-collared longspur, western meadowlark, grasshopper sparrow and lark bunting) of my focus species occurrence and/or densities, while having a positive effect on the bobolink.;At the patch level, chestnut-collared longspur, Sprague's pipit, grasshopper sparrow, savannah sparrow, and western meadowlark occurrences and/or densities were negatively affected by the increasing presence of patch edge surrounded by woody species. Western meadowlarks and grasshopper sparrows were classified as area sensitive, having lower densities in small versus large grassland patches.;Increasing amounts of grassland at the landscape scale positively influenced the occurrence and/or densities of Baird's sparrows, chestnut-collared longspurs, dickcissels, grasshopper sparrows, lark buntings, savannah sparrows, and Sprague's pipits. Bobolinks were the only species whose occurrence and density had a negative association to the amount of grass in the surrounding landscape. There was not only variability in the effect the landscape variables had but also at what level they were still important. Baird's and grasshopper sparrow occurrence and densities showed positive associations at the 400m or 800m levels while occurrence and densities of bobolinks, chestnut-collared longspurs, lark buntings, savannah sparrows and Sprague's pipits were influenced up to the 1600m or 3200m levels.;These models supply baseline data to managers for preservation and restoration of grassland habitat to help maintain populations of grassland obligate bird species. To maintain current populations and species diversity, it is critical that managers preserve as much native grassland as possible. Due to the diverse habitat requirements of these species of concern grasslands should be under varying management regimes ranging from idle to heavily grazed or mowed. Reduction and removal of exotic plant species should be a key element in establishing habitat for grassland obligate species as many were negatively affected by increases in exotic plant coverage. Preserved patches should be large in size as some species were area sensitive and preferred patches .250-1600ha. Grassland patches should also have little to no woody edge. Finally, these patches should be located in close proximity to one another, or in areas of little fragmentation, to help increase the amount of grassland habitat in the landscape, as many of these grassland bird species were positively associated with the landscape variables, some up to 3200m.