Spotted owl foraging patterns following fuels treatments, Sierra Nevada, California

Abstract

Western dry conifer forests continue to experience increased severe, stand-replacing wildfire that is outside of historical precedent. Fuels treatments, landscape-scale modifications of forest fuels and structure, are likely to remain a management tool to modify fire behavior and restore ecological resilience. The impacts of fuels treatments to listed species such as spotted owls (Strix occidentalis) remain uncertain and are contested because of limited available information. To evaluate spotted owl foraging habitat selection in a landscape recently modified by forest fuels-reduction treatments, we radio-marked and tracked 10 California spotted owls (S. o. occidentalis) for 2 years immediately following fuels treatment installation in the northern Sierra Nevada, California, USA. We categorized fuels treatments into 3 types: mechanical thin, installed within the study area as landscape-scale fire breaks characterized by even tree spacing, open understory, and low canopy cover, or group selections; understory thin, a hand-removal of small trees and shrubs; and understory thin followed by underburn, a controlled surface-fuel burn that left the overstory intact. We described post-treatment habitat using forest structural metrics derived from a Light Detection and Ranging (LiDAR) dataset that was collected 1 year after fuels treatments were completed. We collected 436 spotted owl foraging locations during 2 breeding seasons and evaluated breeding season home range size and composition using a resource selection function. We assessed possible contributors to owl foraging patterns by comparing a priori hypotheses in an information-theoretic approach and using randomly generated points that estimated available habitat. Spotted owl breeding season home ranges contained fuels treatments in proportion to their availability on the landscape and averaged 17.1% treated area. Within the home range, owl foraging locations in the post-treatment landscape were best predicted by lower proportions of gaps than anticipated at random, steeper slopes, and minimized distance from the owl's site center. Our results suggest that moderate to high proportions of gaps, typically a feature of forest fuels reduction and restoration treatments, may reduce the probability of spotted owl foraging. Ó 2018 The Wildlife Society.

Elevational gradients strongly mediate habitat selection patterns in a nocturnal predator

“…Spotted owl nocturnal habitat selection patterns at higher elevations in this study were generally consistent with the results presented in previous studies (Gutiérrez et al 1992, 2017, Irwin et al 2007, Atuo et al 2019, Blakey et al 2019, Gallagher et al 2019). However, habitat selection at lower elevations exhibited a different pattern and was consistent with our hypothesis of elevation‐dependent habitat selection.…”

Managing emerging threats to spotted owls

“…First, 2 recent reports on managing the California spotted owl in the Sierra Nevada Forests (Roberts and North , Gutiérrez et al ) cited multiple northern spotted owl papers to describe the potential negative effects of barred owls on spotted owls (Kroll et al ; Dugger et al ; Yackulic et al , ; Wiens et al ). Second, the recovery plan for the Mexican spotted owl (USDI ) cited northern spotted owl and California spotted owl papers on fire effects extensively (Franklin et al , Lee and Irwin , Ager et al , Bond et al , Clark et al ), and extrapolated information on response to forest treatments from studies on the northern spotted owl and the California spotted owl (Meiman et al , Seamans and Gutiérrez , Gallagher , Dugger et al , Stephens et al ). In all cases this extrapolation of information among subspecies was caused by a lack of information specific to the focal subspecies.…”

Review of the effects of barred owls on spotted owls

“…Also, for territories in which ≥20 ha of mature coniferous forest was altered, California spotted owls experienced a 2.5% decline in occupancy probability. In the northern Sierra Nevada in eastern California, Gallagher () assessed home range sizes of 8 California spotted owls in areas altered by recent fuels treatments, and reported that home range area increased, a sign of declining habitat quality, as the total area of fuels treatments within the home range increased. These fuels treatments, called defensible fire protection zones (DFPZs), reduced canopy cover, tree density, and ladder fuels.…”