Kristel K. Bakker

Area Sensitivity in North American Grassland Birds: Patterns and Processes

Grassland birds have declined more than other bird groups in North America in the past 35–40 years (Vickery and Herkert 2001, Sauer et al. 2008), prompting a wide variety of research aimed at understanding these declines, as well as conservation programs trying to reverse the declines (Askins et al. 2007). Area sensitivity, whereby the pattern of a species’ occurrence and density increases with patch area (Robbins et al. 1989), has been invoked as an important issue in grassland-bird conservation, and understanding the processes that drive area sensitivity in grassland birds is a major conservation need (Vickery and Herkert 2001). Here, we review the literature on North American grassland bird species that is relevant to the following questions. (1) What is the

Planted Grasslands and Native Sod Prairie: Equivalent Habitat for Grassland Birds?

ABSTRACT. Little is known about how avian relationships to tracts of native sod prairie compare with avian relationships to single and multiple species of cool- and warm-season grassland plantings. We compared grassland bird species richness and density in 5 grassland cover types (n = 97) in the tallgrass prairie region of eastern South Dakota and western Minnesota, 2001–2004. Grassland bird species richness was significantly higher in native sod prairies than it was in all planted cover types except warm-season mixes. Grasslands dominated by exotic species did not support as many grassland bird species or have species densities as high as grasslands containing native species. Intermediate wheatgrass monotypes and cool-season mixes comprised of exotic species contained 40%–60% fewer grassland bird species than native sod prairie. Bobolink (Dolichonyx oryzivorus) density was 68% and 51% lower in intermediate wheatgrass monotypes and cool-season mixes, respectively, than it was in switchgrass monotypes. Clay-colored Sparrow (Spizella pallida) density was 75%–91% higher in native sod prairies than it was in any other cover type. Savannah Sparrow (Passerculus sandwichensis) density was 72% higher in native prairie than it was in grasslands dominated by exotic species. We recommend incorporating a diversity of native plant species into grassland plantings for biomass fuels or wildlife, rather than using monotypes or exotic species, to provide habitat for grassland birds. Although replacing croplands with planted grasslands would benefit grassland bird populations, we caution that replacing existing native sod tracts with planted grasslands would be detrimental to populations of several grassland bird species.

Planting Trees in Prairie Landscapes: Do the Ecological Costs Outweigh the Benefits?

Abstract Tree plantings are striking landscape features that symbolize settlement of the West. Although grassland birds require large tracts of treeless grasslands, planting trees in prairie landscapes is still regarded by many as a positive management practice. We compared bird use of tree plantings (n=182) and natural riparian woodlands (n=37) to evaluate whether ecological costs of tree plantings to grassland birds is compensated for by the benefit they provide to forest birds of management concern. Findings indicate that ecological costs of tree plantings outweigh their benefits because they fail to provide habitat for forest birds of management concern. Thus, loss of native grassland bird communities is the currency in which we pay the ecological costs of plantings trees in prairie landscapes. We recommend that managers refrain from planting trees in or adjacent to grassland habitats. We further recommend that managers refocus their tree plantings efforts to restoration of riparian woodlands that maximize avian diversity in prairie landscapes.