Year of Award

2016

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

College of Forestry and Conservation

Committee Chair

David E. Naugle

Commitee Members

Victoria J. Dreitz, Mark Hebblewhite, Paul M. Lukacs, Thomas E. Martin

Abstract

For imperiled species, the hierarchical nature of habitat selection suggests the need for a hierarchical approach to conservation: address threats to persistence operating at broad scales on populations before focusing on the quality of patches or availability of particular resources used by individuals. We apply this approach to conservation and management of habitat for greater sage-grouse (Centrocercus urophasianus) in the eastern portion of their range where cropland conversion continues to fragment sagebrush grasslands. Using locations of active leks in portions of Montana, Wyoming, North Dakota, and South Dakota as spatial indices of populations, we found sage-grouse distribution was highly sensitive to cropland fragmentation in a 12 mi2 landscape. A single square-mile parcel broken out into cropland can thus reduce population persistence within an area twelve times that size, emphasizing the need to conserve large, intact sagebrush landscapes. Simulated cropland buildout scenarios indicate 5-7% of the northern Great Plains population remains vulnerable to future cropland conversion. We demonstrate, however, that with a targeting scheme incorporating biological value, risk, and cost, a $100M investment in conservation easements could reduce potential losses by 80%. Next, using radio-marked birds to locate and monitor nests in a large-scale, replicated, natural grazing experiment in central Montana, we tested hypothesized relationships between livestock grazing and sage-grouse nest site selection and survival and evaluated effects of rest-rotation grazing systems on vegetation structure and nest survival. Surprisingly, we found no evidence that herbaceous vegetation structure affected choice of nest site or nest survival. Instead, females selected nest sites based on relatively static features such as sagebrush cover, terrain roughness, landscape fragmentation, and distance to major roads, while nest survival was affected primarily by severe weather. Rotational grazing systems had negligible effects on upland vegetation structure and no effect on sage-grouse nest survival. Finally, in light of recent research which demonstrated how commonly-used field methods can produce inflated or spurious inference on the relationship between vegetative concealment and nest survival, we reanalyze four independently collected sage-grouse nest datasets to test for relationships between grass height and nest survival. All four datasets indicated strong, positive effects of grass height on nest survival prior to correction for biased timing of vegetation measurement. Once this bias was accounted for, however, none of the datasets supported a positive effect, confirming that plant phenology is largely responsible for previouslyreported relationships between herbaceous hiding cover and nest success in sage-grouse.

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© Copyright 2016 Joseph Tyler Smith