Skip to Main Content
Barred owl occupancy surveys within the range of the northern spotted owlAuthor(s): J. David Wiens; Robert G. Anthony; Eric D. Forsman
Source: The Journal of Wildlife Management. 75(3): 531-538
Publication Series: Scientific Journal (JRNL)
Station: Pacific Northwest Research Station
PDF: Download Publication (1.65 MB)
DescriptionThe range expansion by barred owls (Strix varia) into western North America has raised considerable concern regarding their potential effects on declining northern spotted owl (Strix occidentalis caurina) populations, yet most information on the occurrence of barred owls in the region is limited to incidental detections during surveys for spotted owls. To address this shortcoming we investigated response behavior, detection probabilities, and landscape occupancy patterns of barred owls in western Oregon, USA, during conspecific versus spotted owl call-broadcast surveys, Subtle differences in barred owl response behavior to conspecific versus spotted owl vocalizations combined with minor procedural differences between species-specific survey protocols led to a sizeable difference in estimated detection probabilities during conspecific (0.66, 95% CI = 0.61-0.71) versus spotted owl (0.48, 95% CI = 0.39-0.56) surveys. We identified 61 territorial pairs of barred owls during repeated surveys of a multi-ownership study area with the probability of occupancy being highest in the structurally diverse mixture of mature and old forests that occurred almost entirely on public lands. Our findings suggest that research and management strategies to address potential competitive interactions between spotted owls and barred owls will require carefully designed, species-specific survey methods that account for erratic response behaviors and imperfect detection of both species. Our sampling methods can be used by forest managers to determine the occurrence and distribution of barred owls with high confidence.
- Visit PNW's Publication Request Page to request a hard copy of this publication.
- We recommend that you also print this page and attach it to the printout of the article, to retain the full citation information.
- This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
CitationWiens, J. David; Anthony, Robert G.; Forsman, Eric D. 2011. Barred owl occupancy surveys within the range of the northern spotted owl. The Journal of Wildlife Management. 75(3): 531-538.
Keywordsbarred owl, detection probability, northern spotted owl, occupancy modeling, Oregon, Strix occidentalis caurina, Strix varia
- Modeling co-occurrence of northern spotted and barred owls: accounting for detection probability differences
- The effects of habitat, climate, and Barred Owls on long-term demography of Northern Spotted Owls
- Early detection of rapid Barred Owl population growth within the range of the California Spotted Owl advises the Precautionary Principle
XML: View XML