Graduate Thesis Or Dissertation
 

Local weather, regional climate, and population dynamics of northern spotted owls in Washington and Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/12579v05r

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  • Since the early 1990s, declines in northern spotted owl (Strix occidentalis caurina) populations have been documented through extensive field surveys and range-wide demographic analyses. Although loss of late-successional forest has been credited as the primary cause for spotted owl population declines, environmental variation has also been shown to influence vital rates of many avian species, including spotted owls. Weather and climate are often the most important sources of environmental variation for many species, and population processes can be affected by both large-scale climate fluctuations as well as by local variation in weather. My objectives were to identify associations between weather and climate and demographic rates of northern spotted owls using data collected from marked spotted owls on 6 long-term study areas in Washington and Oregon. I used an information-theoretic approach to rank statistical models representing a priori hypotheses regarding effects of weather and climate on annual survival, reproduction, and realized rate of population change. Annual survival was negatively associated with drier-than-normal conditions on a regional scale at 3 areas, but was also associated with local weather conditions at 3 areas. Number of young fledged per pair per year was negatively associated with cold, wet nesting seasons at 3 areas, although larger-scale weather patterns were associated with reproduction as well. Climate accounted for moderate to high amounts of temporal variation for both survival and reproduction, but little of the spatial variation. My analyses of realized rates of population change indicated continued declines in populations at the 6 study areas, with climate accounting for 3-85% of the temporal variation in lambda. My results suggest that spotted owl populations may face additional challenges if climate in the Pacific Northwest follows the current predictions of year-round warming with warmer, wetter winters and hotter, drier summers in the 21st century.
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