Year of Award

2023

Document Type

Dissertation

Degree Type

Doctor of Philosophy (PhD)

Degree Name

Fish and Wildlife Biology

Department or School/College

Wildlife Biology Program

Committee Chair

Victoria J. Dreitz

Commitee Members

Lorelle I. Berkeley, John S. Kimball, Angela Luis, Paul M. Lukacs

Keywords

grazing, greater sage-grouse, habitat selection, nest success, population

Publisher

University of Montana

Abstract

Greater sage-grouse (Centrocercus urophasianus) abundance has declined across the species’ range due to habitat loss, degradation, and fragmentation. To address this decline, information is needed to guide habitat conservation priorities and population management efforts. This includes information about patterns of habitat selection at multiple spatial scales, habitat and land use variables that affect demographic rates, and population trend estimates. We collected ten years of data (2011-2020) on sage-grouse demographic rates and habitat selection, as well as on vegetation and livestock grazing patterns, to address these topics. We were specifically interested in the effects of a rotational grazing system implemented through the United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) Sage Grouse Initiative (SGI). In Chapter 1, we investigated whether sage-grouse hens select seasonal home ranges based on topographic, grazing, and vegetation variables. We found that hens select for shrub cover across all seasons, with seasonal differences in other variables. We also found that sage-grouse located within livestock pastures select for areas with higher used animal unit months (“used AUMs,” or a measure of the amount of forage grazed) in addition to shrub cover. In Chapter 2, we evaluated the effects of the SGI rotational grazing system on sage-grouse nest success. We found that neither SGI rotational grazing systems nor other indices of livestock use had measurable effects on nest success, but we saw a very minor positive effect of senesced grass height. The majority of interand intra-annual variation in nest success was unexplained by grazing-related variables. Taken together, these results suggest that the patterns of land use and livestock management observed during the study are not affecting sage-grouse in this study area, as there is no evidence for a negative effect of livestock grazing on estimated demographic rates or habitat selection. We note that sagebrush shrublands should remain a key component of sage-grouse conservation strategies, as this land cover type was selected by sage-grouse across seasons and spatial scales. In Chapter 3, we compared two methods of estimating sage-grouse population growth rate, using two different datasets. We found that the population growth rate from annual lek counts was more variable than the growth rate estimated using a matrix model. The population growth rate from the matrix model suggested a 10% decrease over the 10-year study, whereas the lek count estimator suggested a 16% increase over the same period. We suggest that growth rates derived from raw lek counts are interpreted with caution, as they may overestimate population trends relative to other methods due at least in part to observation error.

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