Effects of Barred Owl (Strix varia) Removal on Population Demography of Northern Spotted Owls (Strix occidentalis caurina) in Washington and Oregon, 2015–18

Open-File Report 2019-1074
By: , and 



Populations of Northern Spotted Owls (Strix occidentalis caurina; herineafter referred to as Spotted Owl) have declined throughout the subspecies’ geographic range. Evidence indicates that competition with invading Barred Owls (S. varia) has contributed significantly to 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 initiated a before-after-control-impact (BACI) experiment at three study areas in Oregon and Washington to determine if removal of Barred Owls can improve population trends of Spotted Owls. This report describes research accomplishments and initial results from the first 3.5 years of the study (March 2015–August 2018).

Suggested Citation

Wiens, J.D., Dugger, K.M., Lesmeister, D.B., Dilione, K.E., and Simon, D.C., 2019, Effects of Barred Owl (Strix varia) removal on population demography of Northern Spotted Owls (Strix occidentalis caurina) in Washington and Oregon, 2015–18: U.S. Geological Survey Open-File Report 2019-1074, 17 p., https://doi.org/10.3133/ofr20191074.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Background and Study Objectives
  • Study Areas
  • Methods
  • Preliminary Results, 2015–2018
  • Discussion
  • Acknowledgments
  • References Cited
  • Appendixes 1–2
Publication type Report
Publication Subtype USGS Numbered Series
Title Effects of experimental removal of Barred Owls on population Demography of Northern Spotted Owls in Washington and Oregon—2018 Progress Report
Series title Open-File Report
Series number 2019-1074
DOI 10.3133/ofr20191074
Year Published 2019
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Forest and Rangeland Ecosystem Science Center
Description vi, 17 p.
Country United States
State Oregon, Washington
City Cle Elum
Other Geospatial Oregon Coast Range
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details