Thesis

Habitat Use of Juvenile California Spotted Owls (Strix occidentalis occidentalis) During The Post-Fledging Dependency Period In Northeastern California

ABSTRACT HABITAT USE OF JUVENILE CALIFORNIA SPOTTED OWLS (STRIX OCCIDENTALIS OCCIDENTALIS) DURING THE POST-FLEDGING DEPENDENCY PERIOD IN NORTHEASTERN CALIFORNIA by Master of Science in Biological Sciences California State University, Chico Spring 2009 Habitat components of adult spotted owl nest and roost sites have been extensively studied, however few data exist on the habitat requirements for juvenile spotted owls. I examined habitat use and movements of juvenile California spotted owls during the post-fledging dependency period in 2003 and 2004 in northeastern California. I used radio-telemetry to track fourteen juvenile owls to their roost locations used prior to dispersal. I analyzed movement patterns by mapping all locations and estimating the minimum convex polygon (MCP). The owls used a mean area of 194 ha during this time period, with a mean distance of 220 m between successive locations. I conducted vegetation surveys to measure several habitat variables at 141 juvenile roost sites and at 70 random sites within the nest stands. Using logistic regression, I compared habitat data between used and available areas to test whether the owls selected areas with specific structural components within the nest area. The final model demonstrated that juveniles roosted at sites with higher snag densities and higher canopy closure than at random sites. Dense canopy closure may be important to meet thermoregulatory requirements and to provide protection from predators, while higher snag density may contribute to higher prey densities. High canopy cover (> 70%) should be retained within and near protected activity centers (PACs) to suit the habitat needs of juvenile California spotted owls during this critical life stage.

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