Habitat selection and space use by the California spotted owl (Strix occidentalisoccidentalis): New insights from high resolution GPS tracking data

Background/Question/Methods

1. The California Spotted Owl (Strix occidentalis occidentalis) is declining across much of its range and may be threatened with extinction. Whereas habitat requirements of this species have been previously studied, scientists have only recently had access to technologies and analysis tools needed to characterize individual owls’ movements at high resolution and multiple spatial scales.
2. We investigated movement of California spotted owls using GPS loggers that automated observations of movements at multiple temporal and spatial scales. We used > 17,000 locations from 22 owl seasons to characterize summer home range size, distance from nest, roosting habitat selection, and foraging habitat selection at three spatio-temporal scales. We then used a model selection approach to test whether sex or breeding status influenced home range size, distance travelled from the nest or habitat selection.

Results/Conclusions

3. We found that home range size, distance travelled from the nest and foraging habitat selection were all influenced by sex and breeding status. Home ranges of female owls were triple the size of males, and distances travelled from the nest were 1.3 times farther for females than males, with non-breeding females traveling furthest and visiting up to four other owl territories during the course of a season. Roosting and foraging owls both selected for high canopy cover and stands with large trees with foraging owls showing strongest selection at the largest (landscape) scale. Non-breeding owls were more likely to select open areas than breeding owls at the home range and nightly scales.
4. Our findings support existing literature concerning the importance of old growth forest attributes for both roosting and foraging California Spotted Owls. We have shown that non-breeding females travel large distances from the nest and are likely to visit multiple owl territories within one breeding season. Given the long distances travelled by owls and the importance of old growth attributes for roosting and foraging across multiple scales, connectivity of California Spotted Owl habitat in the landscape is likely to be important for this species.