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Variability in Vegetation Effects on Density and Nesting Success of Grassland Birds

Maiken Winter, Douglas H. Johnson, and Jill A. Shaffer


Abstract: The structure of vegetation in grassland systems, unlike that in forest systems, varies dramatically among years on the same sites, and among regions with similar vegetation. The role of this variation in vegetation structure on bird density and nesting success of grassland birds is poorly understood, primarily because few studies have included sufficiently large temporal and spatial scales to capture the variation in vegetation structure, bird density, or nesting success. To date, no large-scale study on grassland birds has been conducted to investigate whether grassland bird density and nesting success respond similarly to changes in vegetation structure. However, reliable management recommendations require investigations into the distribution and nesting success of grassland birds over larger temporal and spatial scales. In addition, studies need to examine whether bird density and nesting success respond similarly to changing environmental conditions. We investigated the effect of vegetation structure on the density and nesting success of 3 grassland-nesting birds: clay-colored sparrow (Spizella pallida), Savannah sparrow (Passerculus sandwichensis), and bobolink (Dolichonyx oryzivorus) in 3 regions of the northern tallgrass prairie in 1998–2001. Few vegetation features influenced the densities of our study species, and each species responded differently to those vegetation variables. We could identify only 1 variable that clearly influenced nesting success of 1 species: clay-colored sparrow nesting success increased with increasing percentage of nest cover from the surrounding vegetation. Because responses of avian density and nesting success to vegetation measures varied among regions, years, and species, land managers at all times need to provide grasslands with different types of vegetation structure. Management guidelines developed from small-scale, short-term studies may lead to misrepresentations of the needs of grassland-nesting birds.

Key words: Bobolink, clay-colored sparrow, density, Dolichonyx oryzivorus, nesting success, Passerculus sandwichensis, Savannah sparrow, Spizella pallida, tallgrass prairie, variability, vegetation structure.

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This resource is based on the following resource (Northern Prairie Publication 1442):

Winter, Maiken, Douglas H. Johnson, and Jill A. Shaffer.  2005.  Variability in vegetation effects on density and nesting success of grassland birds.  Journal of Wildlife Management 69(1):185-197.

This resource should be cited as:

Winter, Maiken, Douglas H. Johnson, and Jill A. Shaffer.  2005.  Variability in vegetation effects on density and nesting success of grassland birds.  Journal of Wildlife Management 69(1):185-197.  Jamestown, ND: Northern Prairie Wildlife Research Center Online.  http://www.npwrc.usgs.gov/resource/birds/gbvegvar/index.htm  (Version 24AUG2006).


Maiken Winter, State University of New York, College of Environmental Sciences and Forestry, 1 Forestry Drive, Syracuse, NY 13210, USA.  Present address: Lab of Ornithology, Cornell University, 159 Sapsucker Woods Road, Ithaca, NY 14850, USA.  E-mail: mw267@cornell.edu.
Douglas H. Johnson and Jill A. Shaffer, U.S. Geological Survey, Northern Prairie Wildlife Research Center, 8711 37th Street S.E., Jamestown, ND 58401, USA.

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