Date of Award
Master of Science
Agricultural grasslands have replaced native Midwestern prairies in the form of pasture, idle cropland and conservation fields. The condition of these cover types directly and indirectly influences the distribution, variety and productivity of avian populations within these landscapes. CP33 habitat buffers are an incentive-based conservation practice specifically designed to increase upland bird habitat and productivity. Landowners are encouraged to remove row crops from production and return them to early successional grassland habitat along the margin of agricultural fields. However, buffers exhibit a high perimeter-to-area ratio, which may increase negative edge effects, thereby creating sink populations. During the 2013 and 2014 breeding seasons, I assessed grassland bird response to CP33 habitat buffers in southern Illinois. Focal species included the northern bobwhite (Colinus virginianus), dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), field sparrow (Spizella pusilla), indigo bunting (Passerina cyanea), and red-winged blackbird (Agelaius phoeniceus). I used a hierarchical multiscale framework to examine the influence of habitat variables at multiple scales on avian abundance, species richness, and occupancy. I also used this same framework, and logistic exposure modeling, to examine daily survival rates of nests found within CP33 habitat buffers. Multiscale occupancy and logistic exposure models consistently performed better than single-scale models for focal bird species; however, relative importance of local variables and landscape variables differed considerably among focal species. Nest survival rate was not strongly affected by edge effects or edge type. Microhabitat variables were much more influential in predicting nest survival. In my study area, CP33 habitat buffers are unlikely to support source populations for most of the focal grassland bird species I studied. To increase nest survival rates within established CP33 habitat buffers, managers should focus on microhabitat vegetation characteristics. To increase bird occupancy of CP33 habitat buffers in southern Illinois, managers should increase the size of CP33 habitat buffers within a landscape having adequate grassland cover. However, managers should not consider CP33 habitat buffers a panacea for most grassland avian species.
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