Barred owls and forest fragmentation in Oregon Coast range spotted owl sites Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_projects/s4655h33w

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  • Little information is available on northern barred owl (Strix varia varia) life history in the Pacific Northwest but their invasion into northern spotted owl habitat (Strix occidentalis caurina) appears to be significant and detrimental to conservation of the latter species. Forest fragmentation has been suggested as a possible factor in barred owl expansion and competitive advantage over spotted owls but until now, this hypothesis has not been evaluated. Forest fragmentation, elevation, and distance to water was measured in 60 spotted owl nest sites in the Siuslaw National Forest using satellite imagery and a Geographic Information System (GIS). Comparisons were made between sites with and without barred owl detection within 0.8 km and between sites with and without spotted owl displacement by barred owls. Comparison of forest fragmentation between owl sites and 74 random sites within the study area were also made to evaluate performance of the methodology. Total habitat and mean nearest-neighbor distance to habitat were the metrics used to estimate forest fragmentation. Measurements were made in 400, 800, and 1600-meter radius plots around each owl site to investigate effects of scale. Logistic regression was used to draw inferences on the effect of forest fragmentation, elevation, and distance to water on the odds of barred owl detection and spotted owl displacement. These variables were found to have no effect on the odds of detection and displacement in all three plot sizes. This suggests that macrohabitat resource partitioning is not yet occurring and this has implications for the longterm survival of the northern spotted owl.
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