Graduate Thesis Or Dissertation
 

Comparison of Common Ravens in Sage-grouse Core and Non-Core Areas: Assessing Predator Densities Related to Anthropogenic Features

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/t148fq43s

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  • Greater sage-grouse (Centrocercus urophasianus: hereafter sage-grouse) abundance and distribution in North America has declined over the last century. Many factors have contributed to this decline, including habitat loss and fragmentation from human development with an associated potential for increased predation. While human development has been connected to lower sage-grouse demographic rates and their avoidance of anthropogenic features, it also provides an increased number of perch and nesting structures used by avian predators. Development has also been attributed to increases in generalist predator abundance because they thrive in human-influenced environments. Wyoming’s Sage-grouse Core Areas (Core Areas) were developed to add protections to important sage-grouse habitat by reducing development and associated impacts to sage-grouse within these Core Areas. Core Areas have maintained higher sage-grouse trends and numbers of birds compared to Non-Core Areas in Wyoming, which could be partially explained by reduced risk to predation in Core Areas that have lower levels of development. However, we lack a study comparing actual reduction in predation risk, such as predator abundance, within and outside Core Areas. In total, I performed 2,157 avian point counts along 380 8.05-km transects throughout the Wyoming Basin within Wyoming during the summers of 2017 and 2018. During these surveys, I noted all human structures at each survey location, which were added to human disturbance data from available GIS data. I conducted a distance sampling analysis with an N-mixture model to evaluate how anthropogenic features influenced raven density across the Wyoming Basin, setup as a Negative Binomial regression (count model) that simultaneously assessed detection probability as a binomial logistic regression. In addition to assessing how raven density was influenced by anthropogenic features, I further categorized existing Core and Non-Core Areas boundaries based on 1) defined sage-grouse breeding habitat, 2) areas of high relative sage-grouse abundance, and 3) actual development related to disturbance known to negatively influence sage-grouse. I found several anthropogenic features were positively related raven density, including density of agricultural lands, communication towers, roads, and landfills My results also indicated that raven density was lower in undeveloped Core and Non-Core Areas compared to developed Non-Core Areas, where less protections are afforded to sage-grouse. These policy related results in combination with higher raven density around anthropogenic features suggests that Core Areas in the Wyoming Basin currently serve as effective predator management and likely help reduce predation risk on sage-grouse. Human features can have direct effects on how predators utilize the landscape and associated resources. It is important for managers and policy makers to understand the mechanism behind continued sage-grouse population decline and how sage-grouse predators interact with human development. Effective conservation policy related to protected areas relies on how land management interacts with stakeholder land use and understanding how those demands influence the protected species, including predator-prey dynamics.
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  • Pending Publication
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  • 2021-07-02 to 2023-08-03

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