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Characteristics of Old-Growth Forests Associated with Northern Spotted Owls in Olympic National Park

L. Scott Mills, Richard J. Fredrickson and Bruce B. Moorhead
The Journal of Wildlife Management
Vol. 57, No. 2 (Apr., 1993), pp. 315-321
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3809428
Stable URL: http://www.jstor.org/stable/3809428
Page Count: 7
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Characteristics of Old-Growth Forests Associated with Northern Spotted Owls in Olympic National Park
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Abstract

The relationship between northern spotted owls (Strix occidentalis caurina) and old-growth forests is well established, but there are few studies indicating which particular characteristics of these forests are most important to spotted owls. Thus, we compared characteristics of forests at owl response and non-response sites across Olympic National Park to identify the specific features which best predict daytime presence of northern spotted owls in relatively pristine forest. At 32 owl response sites and 230 non-response sites we measured 9 structural and species composition variables thought to be important to spotted owls. Based on these variables, we used stepwise logistic regression to develop models predicting the presence or absence of spotted owls. The accuracy of classifying a given site as a response or non-response site was quite high: 57% and 80% better than chance alone for the eastern and western sides of the Park, respectively. Spotted owls tended to roost and/or nest in stands with high vertical canopy layering; snag diameter also was related to spotted owl occurrence. We conclude that managers should focus increased attention on canopy layering and snag diameter as predictors of spotted owl presence in unharvested forests.

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