Graduate Thesis Or Dissertation


The Role of Grazing and Weather in Nest Predator-Prey Dynamics and Reproductive Success of Sagebrush-obligate Songbirds Public Deposited

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  • Livestock grazing occurs worldwide, spanning over 25% of land globally. Effective conservation of biodiversity relies upon understanding the interactions of agricultural management practices and increasingly variable weather associated with climate change. I evaluated grazing, weather and predator-prey interactions within a grazing experiment in the sagebrush ecosystem of southeastern Oregon. I studied key weather variables, nest predator activity and the nest success rates of two species of sagebrush-obligate songbirds, Brewer’s sparrow (Spizella breweri) and sagebrush sparrow (Artemisiospiza nevadensis) under dormant season grazing, rotational grazing and a no-graze control. I found that while weather was an important factor explaining nest success for both songbird species, nest success for sagebrush sparrows increased in grazed pastures relative to no grazing. Grazing influenced the nest predator community of these songbirds and was likely one mechanism explaining the increase in sagebrush sparrow nest success relative to a no-graze control. Nest predator activity was lower for most predators in rotationally grazed pastures relative to no grazing, and lower rodent and badger activity was associated with higher songbird nest success. Ten species, predominately birds and snakes, were documented on camera depredating failed Brewer’s sparrow and sagebrush sparrow nests. My results suggest that reductions in screening cover caused by grazing within the range of reductions observed in my study do not present a threat to these birds, and conservation should focus on management to mitigate the negative effects of extreme weather on the sagebrush ecosystem and associated wildlife. Grazing can have unexpected indirect effects on wildlife population dynamics, and it is important for managers to understand the mechanisms behind grazing effects. Effective conservation will also rely on understanding how land management interacts with other ecosystem issues such as predator-prey dynamics and increasingly variable weather associated with climate change.
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  • My research was funded by the US Fish and Wildlife Service, Bureau of Land Management and Oregon Beef Council. I also received project and travel support from Oregon State University Extension Service and Eastern Oregon Agricultural Research Center.
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