Spatial distribution of an insular spotted owl population in relation to habitat type and availability in Southern California

Graduation Date

1995

Document Type

Thesis

Program

Other

Program

Thesis (M.S.)--Humboldt State University, Wildlife Management, 1995

Committee Chair Name

R.J. Gutierrez

Committee Chair Affiliation

HSU Faculty or Staff

Keywords

San Bernardino Mountains, Spotted owl-Geographic distribution, Strix occidentalis occidentalis, Spotted owl--Habitat, Humboldt State University -- Theses -- Wildlife Management, California

Abstract

I studied the spatial distribution of California Spotted Owls (Strix occidentalis occidentalis) with respect to habitat type and availability within the San Bernardino Mountains of southern California from May 1987 to November 1992. I located 130 unique owl territories within a 1,890 km² study area. I calculated a minimum crude density of 0.14 owls/km², and an ecological density of 0.40 owls/km². Ninety-five territories had at least one nest during the six years of study. I mapped cover types in the mountain range using spectral analysis of Landsat 5 Thematic Mapper imagery from 1988. I delineated 17 cover types to assess owl habitats. The distribution and density of owls were different among the habitats in which they occurred. Three general habitats occurred in the mountain range: canyon live oak (Ouercus chrysolepis)/big-cone Douglas fir (Pseudotsuga macrocarpa); mixed conifer/hardwood; and mixed conifer. I found 62, 27, and 41 owl territories in each of these habitat types, respectively. The densities of sites in each of the habitats were 0.43, 0.20 and 0.11 sites/km², respectively. The mean nearest neighbor distance of territory centers was 1,564 m with a minimum distance of 664 m. The spatial distribution of observed owl sites was significantly different than expected from a random distribution of sites (X² = 30.71, df = 5, P 0.001). I used multiple concentric plots (3ha, 20ha, 79ha, 177ha, 314ha, and 707ha) around owl nest sites, owl non-nest sites and random sites to test whether owls selected cover types differently than their availability. Both nesting and non-nesting owls used spatial habitat configurations that were different from that at available sites at 3ha, 20ha, 79ha, 177ha, 314ha scales and 3ha, 20ha, 79ha, 177ha, 314ha, and 707ha scales, respectively. However, owl nest sites differed from owl non-nest sites only at the level of 3ha plots. Fragmentation of suitable habitat was significantly greater at non-nesting owl sites and random sites than it was at nesting owl sites. Thus, management plans for the San Bernardino Mountains should include consideration of the distribution, proportions, and fragmentation of the habitats.

https://scholarworks.calstate.edu/concern/theses/1j92gb102

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