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  • Field Studies
    Recent Field Studies
    Completed Field Studies
    Pollock, M. 2009.  Effects of sheep grazing and habitat composition on Brewer's sparrow and vesper sparrow habitat selection and breeding success in mountain big sagebrush steppe. Master

    Abstract:  Livestock grazing is the most common use of sagebrush steppe, which is one of the highest priority habitats for conservation in the United States. The role that grazing may play in influencing habitat quality for grassland and shrubland birds is not well understood. We experimentally implemented various intensities of sheep grazing in mountain big sagebrush steppe in Idaho in 2007 and 2008, and modeled the effects of grazing and vegetation characteristics on two songbird species.

    Brewer’s sparrows (Spizelli breweri) are an abundant sagebrush steppe songbird, but their populations are significantly declining throughout their range. We modeled their nest site selection, nest survival, and clutch size. Models indicated greater nest site selection and larger clutch sizes in lightly grazed patches than either ungrazed or heavily grazed patches. Nest survival models suggested a similar but weaker grazing response. All three demographic measures showed a tolerance for heavier grazing in 2008, following a deep snowpack, than in the drought year of 2007. An apparent preference for nesting in areas with greater herbaceous biomass, as well as greater shrub biomass, suggest that long term grazing related increases in shrub cover may have benefited Brewer’s sparrows, but reduction of herbaceous cover by heavy grazing may reduce suitability of nesting sites.

    Vesper sparrows (Pooecetes gramineus) are a ground nesting grassland songbird often abundant in sagebrush steppe. Demographic responses measured included foraging patch selection, nest site selection, nest survival, and clutch size. Relative to availability within territories, moderately grazed areas were selected more for foraging, whereas nests were most often placed in ungrazed patches. Nest site selection was also associated with greater herbaceous biomass and more forb cover. Nest survival was positively correlated with grazing and negatively correlated with herbaceous biomass and forb cover, suggesting a decoupling of selection and fitness consequence at least at a localized scale. Clutch size did not appear to be affected by grazing.
       
    Our results demonstrate the potential for grazing to have differing effects on various aspects of a species’ demography, as well as the potential influence of weather in outcomes of short term studies. The often inconsistent results among grazing studies may result from the complicating effects of climatic variation, as well as the potential for immediate grazing effects to differ from long term effects. We suggest that fine tuned habitat management for species in grazed ecosystems requires a detailed understanding of the way grazing affects different ecological resources at local and landscape scales. Given the predominance of grazing in habitat critical to declining songbirds such as Brewer’s sparrows, further research on the immediate and long term effects of grazing on songbird productivity and survival in various habitats will have important management implications.

    Recent Field Studies

    Ecological Assessments and Research Supported by the Lava Lake Institute:

    Bradley, B. 2007. Short term impacts of changing grazing regime in central Idaho detected with remote sensing. Princeton University. Princeton, NJ.
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    Bunting, S. and E. Strand. 2008 Enhancing spatial heterogeneity of grazed landscapes: implications to the fire fuel matrix. University of Idaho. Moscow, ID.
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    Carlisle, J. 2007. Analysis of riparian bird population changes in the Pioneer Mountain Foothills at Lava Lake Ranch from 2001-2007. Boise, ID.
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    Caselton Lowe, C. 2008. An examination of insect communities and their response to changes in vegetation structure with emphasis on Coleoptera and Hymenoptera in a sagebrush steppe habitat in south-central Idaho. Master
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    Karl, J, K. Colson, A.R. Sands, and B. Unnasch. 2008. The Landscape Toolbox: Integrating Tools and Methods for Effective Rangeland Management at Multiple Spatial Scales. The Nature Conservancy, Boise, ID.
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    O'Sullivan, M.T., K. Murray, and S. Bergen. 2009. Maintaining Connectivity for Wide-Ranging Species: Pronghorn Migration Routes and Crucial Habitat in the Lost River Sinks Landscape. Hailey, ID.
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    . . . . . . . . . . . . . . . . . . . . . . .  Abstract at left . . . . . . . . . . . . . . . . . . . . . . .

    Pollock, M. 2009.  Effects of sheep grazing and habitat composition on Brewer's sparrow and vesper sparrow habitat selection and breeding success in mountain big sagebrush steppe. Master
    Read abstract >

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    Strand, E., S. Bunting, and M.T. O'Sullivan. 2008. Change detection in quaking aspen using current and historical aerial photography. University of Idaho. Moscow, ID.
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    Wijayrante, U.C. and D. A. Pyke. 2007. Investigating seed longevity of Mountain and Wyoming Big Sagebrush. Forest and Rangeland ecosystem Science Center, USGS. Corvallis, OR.
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    Zaroban, D. 2008. Distribution, habitat use, ranging behavior, and disturbances influencing the Wood River sculpin. Department of Environmental Quality. Boise, ID.
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    P. O. Box 2249 • Hailey, Idaho 83333 • Phone 208.788.1378 • Fax 208.788.1264 • info@lavalakeinstitute.org
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