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Habitat selection by northern spotted owls in mixed-coniferous forests

Authors

  • Larry L. Irwin,

    Corresponding author
    1. National Council for Air and Stream Improvement, Inc., 3816 Salish Trail, P.O. Box 68, Stevensville, MT 59870, USA
    Current affiliation:
    1. National Council for Air and Stream Improvement, Inc., P.O. Box 68, Stevensville, MT 59870, USA.
    • National Council for Air and Stream Improvement, Inc., 3816 Salish Trail, P.O. Box 68, Stevensville, MT 59870, USA.
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  • Dennis F. Rock,

    1. National Council for Air and Stream Improvement, Inc., 43613 NE 309th Ave., Amboy, WA 98601, USA
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  • Suzanne C. Rock

    1. National Council for Air and Stream Improvement, Inc., 43613 NE 309th Ave., Amboy, WA 98601, USA
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  • Associate Editor: David Euler.

Abstract

Conservation planning for the federally threatened northern spotted owl (Strix occidentalis caurina) requires an ability to predict their responses to existing and future habitat conditions. To inform such planning we modeled habitat selection by northern spotted owls based upon fine-scale (approx. 1.0 ha) characteristics within stands comprised primarily of mixed-aged, mixed coniferous forests of southwestern Oregon and north-central California. We sampled nocturnal (i.e., primarily foraging) habitat use by 71 radio-tagged spotted owls over 5 yr in 3 study areas and sampled vegetative and physical environmental conditions at inventory plots within 95% utilization distributions of each bird. We compared conditions at available forest patches, represented by the inventory plots, with those at patches used by owls using discrete-choice regressions, the coefficients from which were used to construct exponential resource selection functions (RSFs) for each study area and for all 3 areas combined. Cross-validation testing indicated that the combined RSF was reasonably robust to local variation in habitat availability. The relative probability that a fine-scale patch was selected decreased nonlinearly with distances from nests and streams; varied unimodally with increasing average diameter of coniferous trees and also with increasing basal area of Douglas-fir (Pseudotsuga menziesii) trees; increased linearly with increasing basal areas of sugar pine (Pinus lambertiana) and hardwood trees and with increasing density of understory shrubs. Large-diameter trees (>66 cm) appeared important <400 m from nest sites. The RSF can support comparative risk assessments of the short- versus long-term effects of silvicultural alternatives designed to integrate forest ecosystem restoration and habitat improvement for northern spotted owls. Results suggest fine-scale factors may influence population fitness among spotted owls. © 2011 The Wildlife Society.

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