Multi-scale associations of grassland birds in response to cost-share management of conservation reserve program fields in Illinois

Abstract

The Illinois State Wildlife Action Plan targeted the Conservation Reserve Program (CRP) as important improvable acres for grassland and grassland-successional bird species of greatest need for conservation. A large portion of CRP grasslands in Illinois and elsewhere lack floristic and structural diversity because of the absence of management and the extensive planting of monotypic grasses such as tall fescue (Schedonorus phoenix). The 2006 Farm Bill included the mid-contract management (MCM) provision requiring landowners with new CRP enrollments to provide habitat improvement midway through the 10–15-year contract duration. We compared the effects of 3 approved MCM regimes (i.e., fall strip disking, fall glyphosate spraying, fall glyphosate spraying followed by spring legume drill-seeding) on grassland bird communities in 60 tall fescue-dominated CRP fields in south-central Illinois during 2006–2008. We modeled relative density of dickcissels (Spiza americana), Henslow's sparrows (Ammodramus henslowii), and eastern meadowlarks (Sturnella magna) as a function of microhabitat, patch-level patterns, and landscape composition using a multi-scale assessment approach. We detected 10 grassland-associated bird species (e.g., Henslow's sparrow, northern bobwhite [Colinus virginianus], sedge wren [Cistothrus platensis], Savannah sparrow [Passerculus sandwichensis], grasshopper sparrow [Ammodramus savannarum]) that are recognized as species of greatest need for conservation under the Illinois State Wildlife Action Plan. Mean total bird densities and species richness were greater in glyphosate-sprayed fields (5.0 birds/ha; 11.5 species) and glyphosate drill-seeded fields (4.4 bird/ha; 12.4 species) than in disked (3.4 birds/ha; 8.7 species) and reference (3.1 birds/ha; 7.5 species) fields. The avian conservation value of glyphosate sprayed and glyphosate drill-seeded fields increased 34.2% and 32.6% post-management, respectively, but we did not detect change in disked and reference fields. Our models indicate that density of each of the focal species is likely associated with changes in plant species diversity and habitat structure resulting from management actions but is also influenced by landscape composition. Despite an overall positive response of the grassland bird communities to glyphosate-based treatment regimes in tall fescue CRP fields in south-central Illinois, the response of Henslow's sparrow density to glyphosate was not consistently positive. © 2013 The Wildlife Society.