Spotted Owl Home Range and Habitat Use in Southern Oregon Coast Ranges

Abstract

We radiotracked 9 adult spotted owls (Strix occidentalis) in the southern Oregon Coast Ranges for 6-12 months. Owls selected home ranges that emphasized old growth within the landscape. Minimum convex polygon home ranges of 4 pairs were 1,153-3,945 ha and contained 726-1,062 ha of old growth. The percentages of. the home ranges in old growth were 25-73%. Home-range size expanded significantly (P < 0.05) with decreasing proportions of old growth (r = -0.83). The amount of old growth in the pair home ranges was less variable than was home-range size. Old growth was selected by the owls for foraging and roosting (P < 0.05); clearcuts and other nonforested areas were not used. Early to middle stages of forest development were used either less than or in proportion to their availability within the home ranges, even where old growth was scarce. J. WILDL. MANAGE. 54(1):11-17 _____________________________________________________________________________________________ Spotted owl management in the Pacific Northwest is controversial because it involves a mix of biological, economic, political, and social issues (Heinrichs 1983, Strong 1987). Spotted owls are associated with commercially valuable old-growth, coniferous forests (Carey 1985). Habitat management rests primarily on 3 telemetry studies of habitat use and home-range sizes (Forsman et al. 1984, Gutierrez et al. 1984, Forsman and Meslow 1985) and various unpublished reports (see Marcot and Holthausen 1987). Only 1 study (Forsman et al. 1984 as supplemented by Forsman and Meslow 1985) is reported in detail. Dawson et al. (1987) conclude that precise information on the owl's habitat needs will be necessary to resolve the controversy over the preservation of the species. Forsman et al. (1984) and Forsman and Meslow (1985) report habitat use, home-range sizes, and the composition of home ranges of 8 adult owls radiotracked for 9-12 months in the central Oregon Cascade Range and 6 adult owls tracked for 4 months in the central Oregon Coast Ranges. Gutierrez et al. (1984) tracked 8 owls for up to 1 year in the North Coast Range of California; they provide only an overview of their study. Our objectives were to determine the home-range sizes, home-range composition, habitat use, and response to forest fragmentation of spotted owls across a large landscape, the southern Oregon Coast Ranges. We wanted to assess if the results reported by Forsman and Meslow (1985) could be generalized and to determine possible geographic differences in the habitat of spotted owls in the Western Hemlock Zone of Oregon, as described by Franklin and Dyrness (1973). A. Strassler and P. Christgau provided field assistance; P. Carson was especially helpful in mapping owl home ranges. R. Bown, J. Lint, J. Mires, F. Oliver, J. Witt, and numerous other employees of the Roseburg District of the Bureau of Land Management provided invaluable assistance. Funding was provided by the Oregon State Office of the Bureau of Land Management in cooperation with the U.S. Forest Service’s Old Growth Wildlife Habitat Program. This is contribution 97 of the Old Growth Program. E. Forsman, M. Fuller, G. Gould, N. Green, R. Gutierrez, J. Lint, B. Mannan, C. Meslow, G. Miller, N. Tilghman, R. Reynolds, and J. Verner reviewed earlier draft manuscripts.