Date of Award:
5-1-1995
Document Type:
Thesis
Degree Name:
Master of Science (MS)
Department:
Biology
Department name when degree awarded
Biology
Committee Chair(s)
Kimberly A. Sullivan
Committee
Kimberly A. Sullivan
Committee
Gary E. Belovsky
Committee
James A. Gessaman
Abstract
I conducted several habitat analyses that describe the striking similarity in habitat resource use of nesting Northern Goshawks, Accipiter gentilis atricapillus, and Northern Spotted Owls, Strix occidentalis caurina. The theoretical context of my work was the Compression Hypothesis described by Schoener in 1974, which proposed that the primary ecological dimension to show effects of competition in the first nonevolutionary stages of species overlap is habitat (vs. time and food dimensions). The study was conducted in the southern Cascades of northern California and southern Oregon, east of the Cascade crest. I conducted both understory and overstory analyses of forest structure. The openness of the understory was important in differentiating goshawk and owl sites. The overstory, which is biologically tied to the understory by growth dynamics, was in turn also expected to show variable differences in the goshawk and owl stands. The analyses led to the conclusion that the Northern Goshawk nests in stands with a more pronounced open understory and denser overstory in comparison to stands selected by Northern Spotted Owls. To assess the possible effects of competition on habitat use, forest stands where both species nested successfully were termed sympatric and compared to stands that supported only one species (termed allopatric). Although inconclusive from these analyses, the most parsimonious conclusion is that the Northern Spotted Owl has an included niche with respect to the Northern Goshawk. I also address management recommendations and suggest that although the Northern Goshawk is a species that can nest in stands typical of the type Northern Spotted Owls use, the goshawk is associated with a more open understory, typical of the structure of mixed-conifer stands before the advent of natural fire suppression. For this reason, the Northern Goshawk seems a better candidate as the indicator species of the southern Cascade forests, east of the Cascade crest
Recommended Citation
Rissler, Leslie J., "Habitat Structure Analyses of Northern Goshawk, Accipiter gentilis atricapillus, And Northern Spotted Owl, Strix occidentalis caurina, Nesting Stands in the Eastern Cascades" (1995). Biology. 618.
https://digitalcommons.usu.edu/etd_biology/618
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