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Nest Structures and Habitats of the Northern Spotted Owl in Three Ecological Subregions of British Columbia

Author(s) or contact(s): F.L. Waterhouse, I.A. Manley, A.S. Harestad, and P.K. Ott
Source: Coast Forest Region
Series: Technical Report
Other details:  Published 2012. Hardcopy is available.


Fourteen nest sites of the endangered Northern Spotted Owl (Strix occidentalis caurina) in British Columbia were sampled in 2003 and 2004. Nests were located in three broad ecosystem types: the maritime (n = 1), submaritime (n = 6), and continental (n = 7) ecological subregions. Spotted Owls exhibited flexibility in their use of different types of nest structures across their broad ecological distribution. Most nests occurred in chimney top or side cavities of large diameter (average 98 cm dbh) trees and snags (79%) with fewer found on platform type structures (21%). Although a variety of tree species provided nest structures, the largest proportion were Douglas-fir (Pseudotsuga menziesii; 79%). There was little evidence that Spotted Owls selected for particular habitat attributes in the immediate area surrounding the nest (patch-level selectivity) within the nest stands, except for higher densities of small trees (< 10 cm dbh) and lower densities of mid-size snags (30-50 cm dbh). Older forest stands (> 140 years old) adjacent to the nest stand were defined as the local landscape. Stand-level selectivity within the local landscape was indicated because nest stands had significantly taller trees than adjacent stands. Nest stands were not uniformly distributed across available aspects (10-290); most (92%) were on southerly and or eastern aspects, but the importance of aspect within the broader regional landscape is unknown. Findings from our study using a small sample of Northern Spotted Owl nest sites in British Columbia appear consistent with those from studies in the United States. The findings of our study support provisioning for nesting habitat over the long term, as undertaken in the current Spotted Owl Management Plan (SOMP2).

Keywords: Northern Spotted Owl, Strix occidentalis caurina, nest site, nest structure, nest habitat, British Columbia, Spotted Owl Management Plan

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Updated March 30, 2012