U.S. Department of Agriculture: Animal and Plant Health Inspection Service

 

Authors

Katie M. Dugger, Oregon State UniversityFollow
Eric D. Forsman, USDA Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, Corvallis, Oregon
Alan B. Franklin, USDA APHIS National Wildlife Research CenterFollow
Raymond J. Davis, USDA Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, Corvallis, Oregon
Gary C. White, Colorado State University - Fort CollinsFollow
Carl J. Schwarz, Simon Fraser University
Kenneth P. Burnham, Colorado State University
James D. Nichols, U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel, Maryland
James E. Hines, U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel, Maryland
Charles B. Yackulic, U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, Arizona
Paul F. Doherty Jr., Colorado State University
Larissa Bailey, Colorado State University
Darren A. Clark, Oregon State University
Steven H. Ackers, Oregon State University
Lawrence S. Andrews, Oregon State University
Benjamin Augustine, Virginia Tech
Brian L. Biswell, USDA Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, Olympia, Washington
Jennifer Blakesley, Rocky Mountain Bird Observatory, Fort Collins, Colorado
Peter C. Carlson, Colorado State University
Matthew J. Clement, U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel, Maryland
Lowell V. Diller, Green Diamond Resource Company, Korbel, California
Elizabeth M. Glenn, U.S. Fish and Wildlife Service, Portland, Oregon
Adam Green, Colorado State University
Scott A. Gremel, USDI National Park Service, Olympic National Park, Port Angeles, Washington
Dale R. Herter, Raedeke Associates, Seattle, Washington
J. Mark Higley, Hoopa Tribal Forestry, Hoopa, California
Jeremy Hobson, USDA Forest Service, Pacific Northwest Region, Springfield, Oregon
Rob B. Horn, USDI Bureau of Land Management, Roseburg District Office, Roseburg, Oregon
Kathryn P. Huyvaert, Colorado State University
Christopher McCafferty, Oregon State University
Trent McDonald, West, Inc., Laramie, Wyoming
Kevin McDonnell, Oregon State University
Gail S. Olson, Washington Department of Fish and Wildlife, Olympia, Washington
Janice A. Reid, USDA Forest Service, Pacific Northwest Research Station, Roseburg Field Station, Roseburg, Oregon
Jeremy Rockweit, Colorado State University
Viviana Ruiz, Colorado State University
Jessica Saenz, Oregon State University
Stan G. Sovern, Oregon State University

Date of this Version

2016

Citation

The Condor: Ornithological Applications 118:57–116

Comments

U.S. Government Work

Abstract

Estimates of species’ vital rates and an understanding of the factors affecting those parameters over time and space can provide crucial information for management and conservation. We used mark–recapture, reproductive output, and territory occupancy data collected during 1985–2013 to evaluate population processes of Northern Spotted Owls (Strix occidentalis caurina) in 11 study areas in Washington, Oregon, and northern California, USA. We estimated apparent survival, fecundity, recruitment, rate of population change, and local extinction and colonization rates, and investigated relationships between these parameters and the amount of suitable habitat, local and regional variation in meteorological conditions, and competition with Barred Owls (Strix varia). Data were analyzed for each area separately and in a meta-analysis of all areas combined, following a strict protocol for data collection, preparation, and analysis. We used mixed effects linear models for analyses of fecundity, Cormack-Jolly-Seber open population models for analyses of apparent annual survival (ɸ), and a reparameterization of the Jolly-Seber capture–recapture model (i.e. reverse Jolly-Seber; RJS) to estimate annual rates of population change (λRJS) and recruitment. We also modeled territory occupancy dynamics of Northern Spotted Owls and Barred Owls in each study area using 2-species occupancy models. Estimated mean annual rates of population change (λ) suggested that Spotted Owl populations declined from 1.2% to 8.4% per year depending on the study area. The weighted mean estimate of λ for all study areas was 0.962 (±0.019 SE; 95% CI: 0.925–0.999), indicating an estimated range-wide decline of 3.8% per year from 1985 to 2013. Variation in recruitment rates across the range of the Spotted Owl was best explained by an interaction between total winter precipitation and mean minimum winter temperature. Thus, recruitment rates were highest when both total precipitation (29 cm) and minimum winter temperature (-9.5˚C) were lowest. Barred Owl presence was associated with increased local extinction rates of Spotted Owl pairs for all 11 study areas. Habitat covariates were related to extinction rates for Spotted Owl pairs in 8 of 11 study areas, and a greater amount of suitable owl habitat was generally associated with decreased extinction rates. We observed negative effects of Barred Owl presence on colonization rates of Spotted Owl pairs in 5 of 11 study areas. The total amount of suitable Spotted Owl habitat was positively associated with colonization rates in 5 areas, and more habitat disturbance was associated with lower colonization rates in 2 areas. We observed strong declines in derived estimates of occupancy in all study areas. Mean fecundity of females was highest for adults (0.309 ± 0.027 SE), intermediate for 2-yr-olds (0.179 ± 0.040 SE), and lowest for 1-yr-olds (0.065 ± 0.022 SE). The presence of Barred Owls and habitat covariates explained little of the temporal variation in fecundity in most study areas. Climate covariates occurred in competitive fecundity models in 8 of 11 study areas, but support for these relationships was generally weak. The fecundity meta-analysis resulted in 6 competitive models, all of which included the additive effects of geographic region and annual time variation. The 2 top-ranked models also weakly supported the additive negative effects of the amount of suitable core area habitat, Barred Owl presence, and the amount of edge habitat on fecundity. We found strong support for a negative effect of Barred Owl presence on apparent survival of Spotted Owls in 10 of 11 study areas, but found few strong effects of habitat on survival at the study area scale. Climate covariates occurred in top or competitive survival models for 10 of 11 study areas, and in most cases the relationships were as predicted; however, there was little consistency among areas regarding the relative importance of specific climate covariates. In contrast, meta-analysis results suggested that Spotted Owl survival was higher across all study areas when the Pacific Decadal Oscillation (PDO) was in a warming phase and the Southern Oscillation Index (SOI) was negative, with a strongly negative SOI indicative of El Niño events. The best model that included the Barred Owl covariate (BO) was ranked 4th and also included the PDO covariate, but the BO effect was strongly negative. Our results indicated that Northern Spotted Owl populations were declining throughout the range of the subspecies and that annual rates of decline were accelerating in many areas. We observed strong evidence that Barred Owls negatively affected Spotted Owl populations, primarily by decreasing apparent survival and increasing local territory extinction rates. However, the amount of suitable owl habitat, local weather, and regional climatic patterns also were related to survival, occupancy (via colonization rate), recruitment, and, to a lesser extent, fecundity, although there was inconsistency in regard to which covariates were important for particular demographic parameters or across study areas. In the study areas where habitat was an important source of variation for Spotted Owl demographics, vital rates were generally positively associated with a greater amount of suitable owl habitat. However, Barred Owl densities may now be high enough across the range of the Northern Spotted Owl that, despite the continued management and conservation of suitable owl habitat on federal lands, the long-term prognosis for the persistence of Northern Spotted Owls may be in question without additional management intervention. Based on our study, the removal of Barred Owls from the Green Diamond Resources (GDR) study area had rapid, positive effects on Northern Spotted Owl survival and the rate of population change, supporting the hypothesis that, along with habitat conservation and management, Barred Owl removal may be able to slow or reverse Northern Spotted Owl population declines on at least a localized scale.

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