Cooperative Fish and Wildlife Research Units Program: Oregon
Education, Research and Technical Assistance for Managing Our Natural Resources

Oregon Project

The demography of Northern Spotted Owls in Oregon and Washington

April 2010 - June 2024

Personnel

Participating Agencies

  • Pacific Northwest Research Station
  • US Fish and Wildlife Service
  • U.S. Fish and Wildlife Service
  • Rogue-Siskiyou National Forest
  • USDA Forest Service

The Northern Spotted Owl (Strix occidentalis caurina) is listed as Threatened under the Endangered Species Act, primarily because of the loss of old growth forest habitat due to timber harvest. The Northwest Forest Plan was developed in the mid-1990's to conserve the owl and other old growth species, while allowing greatly reduced levels of commercial timber harvest on federal land. The Plan required the implementation of a regional effectiveness monitoring program for the spotted owl. This research project collects and analyzes data from 5 of the 7 spotted owl effectiveness monitoring program study areas across the owl's range. Data from this work is used to regularly evaluate population trends of spotted owls, as well as increase our understanding of owl ecology, including dispersal, diet, nest site selection, behavior, genetics, and response to a recent, congeneric invader, the Barred Owl (Strix varia).

Research Publications Publication Date
Yackulic, CB, LL Bailey, KM Dugger, RJ Davis, AB Franklin, ED Forsman, SH Ackers, LS Andrews, LV Diller, SA Gremel, KA, Hamm, DR Herter, JM Higley, RB Horn, C McCafferty, JA Reid, JT Rockweit, and, SG Sovern. 2019. The past and future roles of competition and habitat in the range-wide occupancy dynamics of northern spotted owls: Ecological Applications, 29(3) e01861, doi.org/10.1002/eap.1861. April 2019
Sovern, S.G., E.D. Forsman, K.M. Dugger, and M.Taylor. 2015. Habitat use by northern spotted owls during natal dispersal. Journal of Wildlife Management 79:254-262. January 2015
Sovern, S.G., D.B. Lesmeister, K.M. Dugger, M.S. Pruett, R.J. Davis, and J.M. Jenkins. 2019. Activity Center Selection by Northern Spotted Owls. Journal of Wildlife Management 83:714-727; https://doi.org/10.1002/jwmg.21632 January 2019
Schilling, J.W., K.M. Dugger and R.G. Anthony. 2013. Survival and home-range size of northern spotted owls in southwestern Oregon. Journal of Raptor Research 47:1-14. March 2013
Rockweit, JT, KM Dugger, DB Lesmeister, RJ Davis, AB Franklin, and JM Highley. 2024. Changing Fire Regimes and Nuanced Impacts on a Critically Imperiled Species. Biological Conservation 296 (2024) 110701, DOI:10.1016/j.biocon.2024.110701. | Download July 2024
Olson, GS, RG Anthony, ED Forsman, SH Ackers, PJ Loschl, JA Reid, KM Dugger, EM Glenn, and WJ Ripple. 2005. Modeling of site occupancy dynamics of northern spotted owls in Oregon, including the effects of barred owl encroachment. Journal of Wildlife Management 69:918-932. October 2005
Miller, M.P., Haig, S.M., Forsman, E.D., Anthony, R.G., Diller, L., Dugger, K.M., Franklin, A.B., Gremel, S.A., Lesmeister, D.B., Higley, M., Herter, D.R., Sovern, S.G., 2018, Variation in inbreeding rates across the range of Northern Spotted Owls (Strix occidentalis caurina)- insights from over 30 years of monitoring data: The Auk: Ornithological Advances, v. 135, no. 4, p. 821-833, https://doi.org/10.1642/AUK-18-1.1. July 2018
Jenkins, JMA, DB. Lesmeister, ED Forsman, KM Dugger, SH Ackers, LS Andrews, CE McCafferty, MS Pruett, JA Reid, SG Sovern, RB Horn, SA Gremel, JD Wiens, and Z Yang. 2019. Social status, forest disturbance, and barred owls shape long-term trends in breeding dispersal distance of Northern Spotted Owls. The Condor 121:1–17, DOI: 10.1093/condor/duz055 December 2019
Forsman, ED, RG Anthony, KM Dugger, EM Glenn, AB Franklin, GC White, CJ Schwarz, KP Burnham, DR Anderson, JD Nichols, JE Hines, JB Lint, RJ Davis, SH Ackers, LS Andrews, BL Biswell, PC Carlson, LV Diller, SA Gremel, DR Herter, JM Higley, RB Horn, JA Reid, J Rockweit, J Schaberel, TJ Snetsinger, and SG Sovern. 2011. Population demography of northern spotted owls. Studies in Avian Biology 40. September 2011
Dugger, KM, RG Anthony, and LS Andrews. 2011. Transient dynamics of invasive competition: barred owls, spotted owls and the demons of competition present. Ecological Applications 21:2459-2468. October 2011
Dugger, KM, FF Wagner, RG Anthony, GS Olson. 2005. The relationship between habitat characteristics and demographic performance of Northern Spotted Owls in southern Oregon. Condor 107:865-880. October 2005
Dugger, K. M., E. D. Forsman, A. B. Franklin, R. J. Davis, G. C. White, C. J. Schwarz, K. P. Burnham, J. D. Nichols, J. E. Hines, C. B. Yackulic, P. F. Doherty, Jr., L. Bailey, D. A. Clark, S. H. Ackers, L. S. Andrews, B. Augustine, B. L. Biswell, J. Blakesley, P. C. Carlson, Matthew J. Clement, L. V. Diller, E. M. Glenn, A. Green, S. A. Gremel, D. R. Herter, J. M. Higley, J. Hobson, R. B. Horn, K. P. Huyvaert, C. McCafferty, T. McDonald, K. McDonnell, G. S. Olson, J. A. Reid, J. Rockweit, V. Ruiz, J. Saenz, S. G. Sovern. 2016. The effects of habitat, climate and Barred Owls on long-term demography of Northern Spotted Owls. The Condor: Ornithological Applications Volume 118:57–116, DOI: 10.1650/CONDOR-15-24.1 February 2016
Duchac, L.S., D.B. Lesmeister, K.M. Dugger, Z.J. Ruff, and R.J. Davis. 2020. Passive acoustic monitoring effectively detects Northern Spotted Owls and Barred Owls over a range of forest conditions. The Condor 122: 1–22, DOI: 10.1093/condor/duaa017. April 2020
Diller, L, K Hamm, D Early, D Lamphear, K Dugger, C Yackulic, C Schwarz, P. Carlson, and T McDonald. 2016. Demographic response of Northern Spotted Owls to Barred Owl removal in Coastal Northern California. Journal of Wildlife Management 80:691-707, DOI: 10.1002/jwmg.1046. April 2016
Davis, RJ, and KM Dugger. 2011. Northwest forest plan–the first 15 years (1994–2008): status and trends of Northern Spotted Owl populations and habitat. USDA Forest Service General Technical Report PNW-GTR-850. October 2011
Anthony, RG, ED Forsman, AB Franklin, DR Anderson, KP Burnham, GC White, CJ Schwarz, JD Nichols, JE Hines, GS Olson, SH Ackers, S Andrews, BL Biswell, PC Carlson, LV Diller, KM Dugger, KE Fehring, TL Fleming, RP Gerhardt, SA Gremel, RJ Gutiérrez, PJ Happe, DR Herter, JM Higley, RB Horn, LL Irwin, PJ Loschl, JA Reid, SS Sovern. 2006. Status and trends in demography of Northern Spotted Owls, 1985-2003. Wildlife Monographs 163:1-47. October 2006
Ackers, S.H., R.J. Davis, K.A. Olsen, and K.M. Dugger. 2014. The evolution of mapping habitat for northern spotted owls (Strix occidentalis caurina): a comparison of photo-interpreted, Landsat, and LiDAR based habitat maps. Remote Sensing of Environment 156:361-373. October 2014
Technical Publications Publication Date
Dugger, KM, S. Ackers, et al. 2016. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 52pp. December 2016
Dugger, KM, S Andrews, et al. 2022. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 30pp. December 2022
Dugger, KM, S Andrews, et al. 2021. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 30pp. December 2021
Dugger, KM, S Andrews, et al. 2019. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 27p. February 2020
Dugger, KM, S Andrews, et al. 2018. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 28p. March 2019
Dugger, KM, S Andrews, et al. 2017. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 33p. January 2018
Dugger, KM, S Andrews, et al. 2016. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 33p. December 2016
Dugger, KM, S Andrews, et al. 2015. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 33p. December 2015
Dugger, KM, S Andrews, et al. 2014. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 24p. December 2014
Dugger, KM, S Andrews, et al. 2013. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 23p. December 2013
Dugger, KM, S Andrews, et al. 2012. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report. 25p. December 2012
Dugger, KM, S Andrews et al. 2011. Demographic Characteristics and Ecology of Spotted Owls (Strix occidentalis caurina) in the Southern Oregon Cascades. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. 30p. January 2011
Dugger, KM, S Ackers, et al. 2022. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 68pp. December 2022
Dugger, KM, S Ackers, et al. 2021. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 68pp. December 2021
Dugger, KM, S Ackers, et al. 2019. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 66pp. December 2019
Dugger, KM, S Ackers, et al. 2018. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 59pp. October 2018
Dugger, KM, S Ackers, et al. 2017. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 59pp. January 2018
Dugger, KM, S Ackers, et al. 2014. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 51pp. December 2014
Dugger, KM, S Ackers, et al. 2013. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 51pp. December 2013
Dugger, KM, S Ackers, et al. 2012. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 55pp. December 2012
Dugger, KM, S Ackers et al. 2015. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. Annual Progress Report, 52pp. December 2015
Dugger, KM, S Ackers et al. 2011. The Demography of Northern Spotted Owls (Strix occidentalis caurina) on the Willamette National Forest, Oregon. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. 51p. January 2011
Dugger, KM, RG Anthony, and LS Lawrence. 2008. Site occupancy dynamics of Northern Spotted Owls relative to Barred Owl occurrence and forest habitat characteristics in the southern Cascades of Oregon. 40pp. Unpublished report on file with: Oregon Cooperative Fish and Wildlife Research Unit, Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331. July 2008
Dugger, KM, RG Anthony, and E Forsman. 2009. Estimating Northern Spotted Owl Detection Probabilities: Updating the USFWS Northern Spotted Owl Survey Protocol. Department of Fisheries and Wildlife, Oregon Cooperative Fish and Wildlife Research Unit, Corvallis, OR October 2009
Dugger, KM, RG Anthony, S Andrews, and F Wagner. 2006. Modeling apparent survival and reproductive success of Northern Spotted Owls relative to forest habitat in the southern Cascades of Oregon. Oregon Cooperative Fish and Wildlife Research Unit, Corvallis, OR. May 2006
Dugger, KM, F Wagner, and RG Anthony. 2005. Identification and evaluation of northern spotted owl habitat in managed forests of southwestern Oregon and the development of silvicultural systems for managing such habitat. Report on Step 3: Predicting northern spotted owl survival and reproductive success from habitat characteristics of managed forests of southwestern Oregon. Oregon Cooperative Fish and Wildlife Research Unit, Corvallis, OR. January 2005
Dugger KM, and LS Andrews. 2017. Apparent occupancy and the reproductive rates of Northern Spotted Owls in the Ashland Watershed, Siskiyou Mountains, southern Oregon 1993-1997, 2005-2016. Annual Report. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. 20pp. May 2017
Dugger KM, and LS Andrews. 2016. Apparent occupancy and the reproductive rates of Northern Spotted Owls in the Ashland Watershed, Siskiyou Mountains, southern Oregon 1993-1997, 2005-2015. Annual Report. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. 17pp. May 2016
Dugger KM, T Tippin, and LS Andrews. 2015. Apparent occupancy and the reproductive rates of Northern Spotted Owls in the Ashland Watershed, Siskiyou Mountains, southern Oregon 1993-1997, 2005-2014. Annual Report. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. 17pp. July 2015
Dugger KM, LS Andrews, et al. 2018. Apparent occupancy and the reproductive rates of Northern Spotted Owls in the Ashland Watershed, Siskiyou Mountains, southern Oregon 1993-1997, 2005-2017. Annual Report. Oregon Cooperative Fish and Wildlife Research Unit (OCFWRU), Department of Fisheries and Wildlife, Oregon State University, Corvallis, Oregon. 19pp. July 2018
Dugger KM, JW Schilling, RG Anthony, and LS Andrews. 2011. Apparent occupancy and the reproductive rates of Northern Spotted Owls in the Ashland Watershed, Siskiyou Mountains, southern Oregon 1993-1997, 2005-2011. Department of Fisheries and Wildlife, Oregon Cooperative Fish and Wildlife Research Unit, Corvallis, OR December 2011
Anthony, RG, FF Wagner, K Dugger, and G Olson. 2002. Identification and evaluation of northern spotted owl habitat in managed forests of southwestern Oregon and the development of silvicultural systems for managing such habitat: Report on Step 2: Analysis of habitat characteristics and owl demography on three density study areas. Oregon Cooperative Fish and Wildlife Research Unit, Corvallis, OR. September 2002
Anthony, RG, ED Forsman, AB Franklin, DR Anderson, KP Burnham, GC White, CJ Schwarz, JD Nichols, JE Hines, GS Olson, SH Ackers, S Andrews, BL Biswell, PC Carlson, LV Diller, KM Dugger, KE Fehring, TL Fleming, RP Gerhardt, SA Gremel, RJ Gutiérrez, PJ Happe, DR Herter, JM Higley, RB Horn, LL Irwin, PJ Loschl, JA Reid, SS Sovern. 2004. Status and trends in demography of Northern Spotted Owls, 1985-2003. Final Report to Interagency Regional Monitoring Program, Portland, OR (peer-reviewed by 4 ESA members). Oregon Cooperative Fish and Wildlife Research Unit, Corvallis, OR. April 2004
Presentations Presentation Date
Rockweit, JT, MA Krawchuk, DM Bell, DB Lesmeister, and KM Dugger. 2025. Old Forest Resilience Increases with Repeated Wildfire. 2025 Joint Meeting of the Oregon Chapter of The Wildlife Society and Oregon Society of American Forester, February 5-7, 2025, Salem, OR. February 2025
Rockweit, JT, KM Dugger, DB Lesmeister, RJ Davis, AB Franklin, and JM Higley. 2024. Nuanced Impact of Wildfire on a Critically Imperiled, Old-forest Species. Annual Conference of the Oregon Chapter of The Wildlife Society, February 14-16, 2024, Hood River, OR. February 2024
Rockweit, JT, KM Dugger, DB Lesmeister, RJ Davis, AB Franklin, and JM Higley. 2024. Changing Fire Regimes and Nuanced Impacts to Northern Spotted Owls. 31st Annual Meeting of The Wildlife Society, October 19-23, 2024, Baltimore, MD. October 2024
Theses and Dissertations Publication Date
Schilling, J.W. 2009. Demography, Home Range, and Habitat Selection of Northern Spotted Owls in the Ashland Watershed. M.S. Thesis, Oregon State University, Corvallis, OR. 129pp. June 2009
Mangan, Anna O. 2018. Effects of habitat characteristics, weather and presence of Barred Owls (Strix varia) on occupancy dynamics and breeding propensity of Northern Spotted Owls (S. occidentalis caurina) in Mount Rainier National Park. M.S. Thesis, Oregon State University, Corvallis, Oregon. 79 pp. June 2018
Lawes, T.J. Homing and Habitat Selection of Experimentally Translocated Pygmy Rabbits in Southeastern Oregon. M.S. Thesis, Oregon State University, Corvallis OR. October 2009
Duchac, Leila S. 2019. Passive acoustic monitoring of owls: two studies in forested landscapes of the Pacific Northwest. M.S. Thesis, Oregon State University, Corvallis, Oregon. 171 pp. August 2019