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UBC Theses and Dissertations

Integrated management of flammulated owl breeding habitat and timber harvest in British Columbia Woudenberg , Astrid Michele van


The Flammulated owl (Otus flammeolus-) is an insectivorous, secondary cavitynester which breeds in old-growth, montane forests of western North America. It is migratory and has been listed as vulnerable by the Committee on the Status of Endangered Wildlife in Canada. The Flammulated owl inhabits mixed pine and Douglasfir (Psuedotsuga menziesii) stands at elevations upwards of 850 meters. The study site was Wheeler Mountain, a 1,600 ha area 10 km north of Kamloops, British Columbia, near the species' northern limit. The area has the largest known population of Flammulated owls in Canada and potential impacts of forest harvesting on its breeding habitat were unknown. A logging moratorium was therefore initiated by the Ministry of Environment after Wheeler Mountain was scheduled for timber harvest by the B.C. Ministry of Forests. This study documented foraging and nesting habitat to develop forest management recommendations that would maintain a Flammulated owl breeding population. Conservative estimates from census work suggest there may up to 24 birds on the study site during migration. Nesting density was recorded at 0.1 pairs per 40 ha. Twelve nest sites were found in both Ponderosa pine (Pinus ponderosa) and Douglas-fir snags and trees (mean DBH 61 cm, range = 33 - 82, SD = 15.8). Data suggest that Ponderosa pine may be preferred for nesting. Radio-telemetry indicated that thickets of dense, regenerating Douglas-fir adjacent to open spaces were critical for foraging habitat and were a smaller component of nesting habitat. Stand structure of foraging habitat was characterized by a range of 22 - 559 stems per 500 m2 and canopy cover less than 15% for the same area. A broad inverse relation between stem density and canopy cover resulted from high stem density and defoliation by Western Spruce Budworm (Choristoneura occidentalis) in lower canopy layers. Windfall and previous selective timber harvests had created openings in foraging areas. The results suggest that stand structure is critical for foraging habitat and that once foraging areas are located by the Flammulated owl, a suitable nesting cavity is sought nearby. The northern aspect of Wheeler Mtn. was used more frequently for nesting. Denser thickets of Douglas-fir on the northern aspect apparently provided greater foraging opportunities because of the higher abundance of Western Spruce Budworm. The denser stand structure also provided security cover for the Flammulated owl from the Barred owl (Strix varia), which was more common on the north aspect. Open stands with no budworm defoliation were not used by Flammulated owls. Uneven-aged management is recommended to maintain the existing stand structure. A selective harvest of Douglas-fir only, scheduled both temporally and spatially, will sustain the heterogeneous stand structure. Small openings that allow regeneration of Douglas-fir thickets (up to 1 ha) and Ponderosa pine trees (2 ha) also will enhance both foraging and nesting habitats. Nesting and foraging habitats should be contiguous and include security cover. Any snags or mature trees of Douglas-fir and Ponderosa pine with existing cavities must be retained. Patches of mature and mid-seral trees should be retained where they occur in densities of 5 or more stems per 500 m2 for future suitable nest-cavities. Habitat for primary cavity-excavators must also be maintained. Suitable nest sites may be limiting the breeding population of the Flammulated owl on Wheeler Mountain.

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