Influence of Disturbance on Avian Communities in Agricultural Conservation Buffers in Mississippi, USA

Introduction: Periodic disturbance of agricultural conservation buffers is required to maintain early successional plant communities for grassland birds. However, a disturbance may temporarily reduce the availability of vegetation cover, food, and nesting sites in a buffer. Objective: Our objective was to determine how the type of disturbance (i.e., prescribed burning, light disking) and time since the last disturbance event in agricultural conservation buffers influence the grassland bird community. Methods: Data collected during line-transect surveys conducted in 46 agricultural conservation buffers in northeast Mississippi during the 2007-2009 breeding seasons (May-early August) demonstrate periodic disturbance through prescribed burning and light disking does not influence breeding bird diversity or density in the buffers. Results: Density of Dickcissels (Spiza americana), Red-winged Blackbirds (Agelaius phoeniceus), and Indigo Buntings (Passerina cyanea) did not differ in the buffers regardless of the type of or time since disturbance. Conclusion: Large effect sizes, however, indicate a potential type two error resulting from this conclusion. Thus, based on relative effect sizes, avian density in undisturbed buffers may be greater than in buffers during their first growing season post-disturbance. Relative effect sizes among estimates also indicate disturbance, namely prescribed burning, may lead to greater densities of breeding birds in agricultural conservation buffers. Though disturbance may initially reduce avian density, it is necessary to maintain long-term early-successional herbaceous habitat in agricultural conservation buffers.

Edge Effects on Avian Diversity and Density of Native Grass Conservation Buffers

Conservation Reserve Program Conservation Practice 33 (CP33: Conservation Buffers for Upland Birds) provides habitat for grassland birds in agriculture-dominated landscapes. However, landscape context and adjacency of other land covers may influence colonization, occupancy, and reproductive performance of breeding grassland birds in buffers. Our objective was to determine how edge effects influence diversity and density of breeding grassland birds in CP33 buffers. Data collected during transect surveys in CP33 buffers at a privately-owned farm in Clay County, Mississippi, USA during the 2007􀀁2009 breeding seasons indicated that buffers with a woody edge had the least diversity and density of grassland and facultative grassland birds. Dickcissels (Spiza americana), the most abundant grassland bird species detected in buffers, had a lower density in woodland-bordered buffers than in grassland-bordered buffers. Red-winged Blackbirds (Agelaius phoeniceus) had a lower density in buffers adjacent to woodlands than buffers adjacent to developed areas and those bordered on both sides by crop fields. Conversely, Indigo Buntings, (Passerina cyanea) a woodland edge species, had the greatest density in woodland-bordered buffers when compared to buffers adjacent to grassland and developed areas. These results demonstrate that adjacency influences colonization processes and conservation design should explicitly incorporate local landscape context in field and farm-scale conservation plans. Where conservation of obligate grassland birds is a primary objective of native grass conservation buffers, avoidance of buffer establishment adjacent to woodlands may maximize environmental services as measured by grassland bird diversity and density.