Dugger K.M.,U.S. Geological Survey |
Forsman E.D.,U.S. Department of Agriculture |
Franklin A.B.,U.S. Department of Agriculture |
Davis R.J.,U.S. Department of Agriculture |
And 33 more authors.
Condor | Year: 2015
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 estimatedapparent 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 variationin 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, andanalysis. We used mixed effects linear models for analyses of fecundity, Cormack-Jolly-Seber open population models for analyses of apparent annual survival (φ), 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 occupancymodels. 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 (60.019 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 totalprecipitation (29 cm) and minimum winter temperature (-9.58C) 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 extinctionrates 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 ratesof 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 2areas. 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 supportfor 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 weaklysupported 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 onapparent 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 inmost 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 Owlsurvival 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 modelthat 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 rangeof 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 increasinglocal 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 Owldemographics, 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 thecontinued 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 ourstudy, 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 habitatconservation and management, Barred Owl removal may be able to slow or reverse Northern Spotted Owl population declines on at least a localized scale. © 2016 Cooper Ornithological Society.
Diller L.V.,Green Diamond Resource Company |
Dumbacher J.P.,California Academy of Sciences |
Bosch R.P.,U.S. Fish and Wildlife Service |
Bown R.R.,U.S. Fish and Wildlife Service |
Gutierrez R.J.,University of Minnesota
Wildlife Society Bulletin | Year: 2014
The barred owl (Strix varia) has invaded the range of the northern spotted owl (S. occidentalis caurina) over the past century. The Northern Spotted Owl Recovery Plan recommended removal experiments to assess both the effect of barred owls on spotted owls and the feasibility of initiating some form of barred owl control to enhance recovery of the northern spotted owl. Concern has been raised that such experiments will be neither feasible nor cost-effective. To assess these and other concerns, we conducted lethal removal of barred owls within 3 areas totaling 85,205 ha in northern California, USA. We collected 73 of 81 territorial barred owls detected from 2009 to 2012 during 122 field visits. It took an average of 2 hr 23 min to collect each barred owl from the time of arrival at a site to the time a collected bird was completely processed for field data. Most barred owls were collected within one-half hour of arrival at a site. Lethal removal of barred owls was rapid, technically feasible, and cost-effective. We provide recommendations for techniques we found to be effective. © 2013 The Wildlife Society.
Lewicki K.E.,Colorado State University |
Huyvaert K.P.,Colorado State University |
Piaggio A.J.,U.S. Department of Agriculture |
Diller L.V.,Green Diamond Resource Company |
Franklin A.B.,U.S. Department of Agriculture
Biological Invasions | Year: 2015
The range of the barred owl (Strix varia) has expanded westward over the past century and now entirely overlaps the range of the federally threatened northern spotted owl (S. occidentalis caurina) in the Pacific Northwest. We compared Haemoproteus blood parasite assemblages among northern spotted owls in their native range and barred owls in both their native and invasive ranges to evaluate predictions of five hypotheses about parasites and biological invasions: (1) Enemy Release, where hosts benefit from a loss of parasites in their invasive range, (2) Enemy of My Enemy, where invasive hosts introduce parasites to naïve native hosts, (3) Parasite Spillback, where invasive hosts act as a new reservoir to native parasites, (4) Increased Susceptibility, where native hosts introduce parasites to naïve invasive hosts, and (5) Dilution Effect, where invasive species act as poor hosts to native parasites and decrease the density of potential hosts in their invasive range. We used haplotype network analyses to identify one haplotype common to both owl species throughout North America, three more haplotypes that appeared to be isolated to the barred owl’s historic range, and a fifth haplotype that was only found in California. Based on infection status and parasite diversity in eastern and western barred owl populations, we found strong support for the Enemy Release Hypothesis. Northern spotted owls had higher parasite diversity and probability of infection than sympatric barred owls, offering some support for the Parasite Spillback and Dilution Effect Hypotheses. Overall, this study demonstrates the complexity of host-parasite relationships and highlights some of the ways in which species’ range expansions may alter such relationships among both invasive and native hosts. © 2014, Springer International Publishing Switzerland (outside the USA).
Olson D.H.,U.S. Department of Agriculture |
Kluber M.R.,Oregon State University |
Kluber M.R.,Green Diamond Resource Company
Herpetological Conservation and Biology | Year: 2014
We examined terrestrial amphibians in managed headwater forest stands in western Oregon from 1998 to 2009. We assessed: (1) temporal and spatial patterns of species capture rates, and movement patterns with distance from streams and forest management treatments of alternative riparian buffer widths and upland thinning; (2) species survival and recapture probabilities; and (3) artificial cover object (ACO) sampling utility. We captured over 1,300 animals, primarily Ensatina eschscholtzii, Plethodon vehiculum, and P. dunni. We found spatial and temporal variation in capture rates over time for P. vehiculum, but these patterns appeared unrelated to forest management treatments. Although captures were evenly distributed between near-stream (< 15 m from stream edge) and upland (> 15 m) ACO arrays, species distributions differed with distance from stream. Most movements were short (< 10 m), near streams, and between adjacent ACOs. Using markrecapture methods (2006−2009) we found no difference in apparent survival among the three species. ACOs were effective, but we offer caveats on their utility. Our results suggest that riparian corridors are highly used by both semi-aquatic and upland salamanders, and movements among surface cover objects occur on the order of a few meters. Headwater riparian areas may act as habitat ‘funnels’ for these animals, where movements are concentrated within and along narrow stream-side zones. Positioning of upland down wood in ‘chains’ extending out from riparian area funnels is proposed to facilitate overland habitat connectivity for salamander dispersal. At larger spatial scales, landscape chains of connectivity may be designed with log links connecting riparian and upland areas. © 2013. Deanna Olson. All Rights Reserved.