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Several species of small , cavity -nesting owls occur in the Sierra Nevada , including in areas impacted by human activities . The owls typically use standing dead trees (snags ) for nest sites . Although descriptive studies exist regarding habitats associations around nest and roost sites , few studies have examined habitat associations at larger spatial scales or relative to certain snag characteristics (e .g . , density , decay class ) . To improve our understanding of the habitat associations of these owls , I compared habitat characteristics at 2 spatial scales around areas of owl detection and non -detection . I also examined distances between conspecifics and heterospecifics to determine if clustering of conspecifics or avoidance of predators occurred . I conducted owl broadcast surveys and snag sampling during the spring and summer of 2006 and 2007 in the Lake Tahoe Basin of central Sierra Nevada . I measured additional habitat variables (e .g . , vegetation cover , distance to roadways ) from pre -existing geographical information system layers . I used stepwise logistic regression to ascertain which variables were influential in predicting owl occurrence . The northern saw -whet owl (Aegolius acadicus ) was the only species detected in sufficient numbers for statistical analysis , with a detection probability of 0 .25 . I detected saw -whets in a wide range of conditions and it appeared that few factors influenced their distribution in the basin . Areas dominated by white fir , however , were correlated with the absence of saw -whets at both the macrohabitat and microhabitat scales . White fir -dominated areas tend to occur on the west side of the basin and it is possible white fir was acting as a proxy for other factors not measured in this study , such as microclimate conditions or prey availability . I was also more likely to find a saw -whet within 1000 m of another saw -whet than within 1000 m of a non -use point , indicating clustering of conspecifics in the basin . While it appears saw -whet needs are being met in the basin , restoration projects are ongoing to decrease both the number of snags and relative abundance of white fir . Continued monitoring of the species is essential to understand potential effects of restoration activities . Suggestions are provided for appropriate timing and effort of future surveys . |
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