Date of Award

12-1-2010

Degree Name

Doctor of Philosophy

Department

Zoology

First Advisor

Sparling, Donald

Abstract

Northern bobwhite (hereafter, bobwhite; Colinus virginianus) have experienced long-term declines in population abundance throughout most of their breeding range. In 2004, the United States Department of Agriculture (USDA) authorized mid-contract management (MCM) to restore early successional plant communities in aging Conservation Reserve Program (CRP) fields. I evaluated the effects of 3 MCM regimes, including fall strip disking, fall herbicide spraying (hereafter, spray), and fall herbicide spraying in combination with spring legume interseeding (hereafter, spray-seed) on nearly 650 ha of tall fescue (Schedonorus phoenix [Scop]. Holub; nomenclature follows USDA plants database; see USDA 2010b) CRP in south-central Illinois, USA, during 2005-2008. The objectives of this study were to: 1) evaluate the compositional and structural responses of the vegetation community to MCM, 2) determine the structural vegetation and landscape composition variables that influenced adult bobwhite relative densities and brood presence in CRP, and 3) assess foraging rates and arthropod prey selection of bobwhite chicks relative to MCM. Spray and spray-seed treatments were more effective than disking at reducing tall fescue cover, increasing plant species diversity, and enhancing the structural characteristics of the plant community that are essential for nesting and brood-rearing bobwhite. Spray-seed and disked treatments increased the percentage of bare ground by burying the dead and dying vegetative biomass beneath the soil surface. However, spraying alone left large amounts of litter accumulation on the soil surface that resulted in a delay in the timing of some annual forbs to recolonize. Plant species composition in sprayed and spray-seeded fields changed from a dense, monoculture of tall fescue to a diverse assemblage of perennial grasses, annual forbs, and legumes that provided habitat for nesting and brood-rearing bobwhite. Adult bobwhite and broods responded positively to spray and spray-seed treatments in this study. Adult relative densities (i.e., number of adult bobwhite observed / ha) were higher in sprayed and spray-seeded fields than in disked and controls. The probability of higher relative densities was greater in fields with higher plant species diversity, and percentages of bare ground and legumes. Conversely, relative densities were negatively associated with higher percentages of grass cover. At the landscape scale, relative densities were positively correlated higher percentages of cropland and pastureland within a 250 m buffer of CRP fields. Sprayed and spray-seeded fields were 39.6% more likely to have broods present than control fields. Whereas disked fields were only 10.0% more likely to have broods than controls. Brood presence was positively correlated with higher percentages of bare ground and negatively correlated with higher percentages of grass cover. Human-imprinted bobwhite chicks consumed a higher abundance and biomass of arthropods in sprayed and spray-seeded fields than in disked and controls, although the abundance of arthropods available was generally highest in control and disked fields. This suggests, therefore, that bobwhite chicks foraging rates are not limited by arthropod availability, but rather, by the structure of the vegetative community and the ability of the chicks to access the food resources. Chicks consumed a higher proportion of hymenopterans, isopods, and lepidopterans than expected from nonrandom feeding indicating that they were actively selecting for particular prey. This research has added to the understanding of restoring bobwhite habitat to tall fescue CRP, and could assist USDA-Natural Resource Conservation Service personnel and other land managers in restoring and maintaining marginally diverse grassland ecosystems in CRP fields for nesting and brood-rearing bobwhite.

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