Patch-and landscape-scale effects on area sensitivity of grassland birds in Iowa

The Iowa landscape has been drastically transformed due to agricultural practices, causing population declines in many grassland bird species. Of greatest concern are bird species that are considered to be area sensitive. The Iowa State Preserve System is composed of tracts of prairies, wetlands, and woodlands that can provide habitat for many grassland bird species. This study provides an inventory of the bird species found in 15 Iowa State Preserves that have a prairie component, focusing on area-sensitive grassland bird species. We examined the hypothesis that area and a combination of area and shape are good predictors of the use of the state preserves by grassland birds. We compared whether area or perimeter-to-area ratio was a better predictor of both individual species presence and overall species richness. Preserve area and perimeter-to-area ratio were not an important predictor for the total number of species found in the preserves (P > 0.05). Area was a better predictor than perimeter-to-area ratio for total number of area-sensitive species. As area increased, the total number of grassland area-sensitive species also increased (R = 0.25, P =0.04). Both area and perimeter-to-area ratio models, when plotted against number of grassland areasensitive species, were significant. The data supported the hypothesis that perimeter-to-area ratio, which reflects both area and shape of the preserves, is a better predictor of the number of area-sensitive grassland bird species found in the preserves (R = 0.32), than just area (R = 0.28). As perimeter-to-area ratio decreases, the number of grassland area-sensitive species