Effects of Barred Owl (Strix varia) Removal on Population Demography of Northern Spotted Owls (Strix occidentalis caurina) in Washington and Oregon—2019 Annual Report

Open-File Report 2020-1089
Prepared in cooperation with the U.S. Fish and Wildlife Service, Bureau of Land Management, and U.S. Forest Service
By: , and 

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Abstract

Strix occidentalis caurina (northern spotted owl; hereinafter referred to as spotted owl) have rapidly declined throughout the subspecies’ geographic range. Competition with invading Strix varia (barred owl) has been identified as an immediate cause of those declines. A pilot study in California showed that removal of barred owls coupled with conservation of suitable habitat conditions can slow or even reverse population declines of spotted owls. It is unknown, however, whether similar results can be obtained in areas with different forest conditions, greater densities of barred owls, and fewer remaining spotted owls. We used a before-after-control-impact experimental design on three study areas with long-term demographic information on spotted owls to determine if removal of barred owls can improve population trends of spotted owls. This report summarizes research accomplishments and initial results from the first 4.5 years (from March 2015 to August 2019) of implementing barred owl removal experiments in Washington and Oregon.

Suggested Citation

Wiens, J.D., Dugger, K.M., Lesmeister, D.B., Dilione, K.E., and Simon, D.C., 2020, Effects of barred owl (Strix varia) removal on population demography of northern spotted owls (Strix occidentalis caurina) in Washington and Oregon—2019 annual report: U.S. Geological Survey Open-File Report 2020–1089, 19 p., https://doi.org/10.3133/ofr20201089.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Study Areas
  • Methods
  • Results
  • Discussion
  • Summary
  • Acknowledgments
  • References Cited
  • Appendix 1. Disposition of Barred Owl Specimens
  • Appendix 2. Multi-Season Occupancy Models Used to Characterize Occupancy Dynamics of Barred Owls
  • Appendix 3. Post-Removal Extinction and Colonization Rates of Barred Owls

Additional publication details

Publication type Report
Publication Subtype USGS Numbered Series
Title Effects of barred owl (Strix varia) removal on population demography of northern spotted owls (Strix occidentalis caurina) in Washington and Oregon—2019 annual report
Series title Open-File Report
Series number 2020-1089
DOI 10.3133/ofr20201089
Year Published 2020
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Forest and Rangeland Ecosys Science Center
Description iv, 19 p.
Country United States
State Oregon, Washington
Online Only (Y/N) Y
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