The past and future roles of competition and habitat in the range-wide occupancy dynamics of Northern Spotted Owls

Slow ecological processes challenge conservation. Short-term variability can obscure the importance of slower processes that may ultimately determine the state of a system. Furthermore, management actions with slow responses can be hard to justify. One response to slow processes is to explicitly concentrate analysis on state dynamics. Here, we focus on identifying drivers of Northern Spotted Owl (Strix occidentalis caurina) territorial occupancy dynamics across 11 study areas spanning their geographic range and forecasting response to potential management actions. Competition with Barred Owls (Strix varia) has increased Spotted Owl territory extinction probabilities across all study areas and driven recent declines in Spotted Owl populations. Without management intervention, the Northern Spotted Owl subspecies will be extirpated from parts of its current range within decades. In the short term, Barred Owl removal can be effective. Over longer time spans, however, maintaining or improving habitat conditions can help promote the persistence of northern spotted owl populations. In most study areas, habitat effects on expected Northern Spotted Owl territorial occupancy are actually greater than the effects of competition from Barred Owls. This study suggests how intensive management actions (removal of a competitor) with rapid results can complement a slower management action (i.e., promoting forest succession)

Range-wide sources of variation in reproductive rates of northern spotted owls

We conducted a range-wide investigation of the dynamics of site-level reproductive rate of northern spotted owls using survey data from 11 study areas across the subspecies geographic range collected during 1993–2018. Our analytical approach accounted for imperfect detection of owl pairs and misclassification of successful reproduction (i.e., at least one young fledged) and contributed further insights into northern spotted owl population ecology and dynamics. Both nondetection and state misclassification were important, especially because factors affecting these sources of error also affected focal ecological parameters. Annual probabilities of site occupancy were greatest at sites with successful reproduction in the previous year and lowest for sites not occupied by a pair in the previous year. Site-specific occupancy transition probabilities declined over time and were negatively affected by barred owl presence. Overall, the site-specific probability of successful reproduction showed substantial year-to-year fluctuations and was similar for occupied sites that did or did not experience successful reproduction the previous year. Site-specific probabilities for successful reproduction were very small for sites that were unoccupied the previous year. Barred owl presence negatively affected the probability of successful reproduction by northern spotted owls in Washington and California, as predicted, but the effect in Oregon was mixed. The proportions of sites occupied by northern spotted owl pairs showed steep, near-monotonic declines over the study period, with all study areas showing the lowest observed levels of occupancy to date. If trends continue it is likely that northern spotted owls will become extirpated throughout large portions of their range in the coming decades

The past and future roles of competition and habitat in the range-wide occupancy dynamics of Northern Spotted Owls

Slow ecological processes challenge conservation. Short-term variability can obscure the importance of slower processes that may ultimately determine the state of a system. Furthermore, management actions with slow responses can be hard to justify. One response to slow processes is to explicitly concentrate analysis on state dynamics. Here, we focus on identifying drivers of Northern Spotted Owl (Strix occidentalis caurina) territorial occupancy dynamics across 11 study areas spanning their geographic range and forecasting response to potential management actions. Competition with Barred Owls (Strix varia) has increased Spotted Owl territory extinction probabilities across all study areas and driven recent declines in Spotted Owl populations. Without management intervention, the Northern Spotted Owl subspecies will be extirpated from parts of its current range within decades. In the short term, Barred Owl removal can be effective. Over longer time spans, however, maintaining or improving habitat conditions can help promote the persistence of northern spotted owl populations. In most study areas, habitat effects on expected Northern Spotted Owl territorial occupancy are actually greater than the effects of competition from Barred Owls. This study suggests how intensive management actions (removal of a competitor) with rapid results can complement a slower management action (i.e., promoting forest succession)

The effects of habitat, climate, and Barred Owls on long-term demography of Northern Spotted Owls

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

Range-wide declines of northern spotted owl populations in the Pacific Northwest: A meta-analysis

The northern spotted owl (Strix occidentalis caurina) inhabits older coniferous forests in the Pacific Northwest and has been at the center of forest management issues in this region. The immediate threats to this federally listed species include habitat loss and competition with barred owls (Strix varia), which invaded from eastern North America. We conducted a prospective meta-analysis to assess population trends and factors affecting those trends in northern spotted owls using 26 years of survey and capture-recapture data from 11 study areas across the owls\u27 geographic range to analyze demographic traits, rates of population change, and occupancy parameters for spotted owl territories. We found that northern spotted owl populations experienced significant declines of 6–9% annually on 6 study areas and 2–5% annually on 5 other study areas. Annual declines translated to ≤35% of the populations remaining on 7 study areas since 1995. Barred owl presence on spotted owl territories was the primary factor negatively affecting apparent survival, recruitment, and ultimately, rates of population change. Analysis of spotted and barred owl detections in an occupancy framework corroborated the capture-recapture analyses with barred owl presence increasing territorial extinction and decreasing territorial colonization of spotted owls. While landscape habitat components reduced the effect of barred owls on these rates of decline, they did not reverse the negative trend. Our analyses indicated that northern spotted owl populations potentially face extirpation if the negative effects of barred owls are not ameliorated while maintaining northern spotted owl habitat across their range

Northern spotted owl reproductive rates

These datasets were used in the prospective meta-analysis of northern spotted owl reproductive rates over 25 years across 11 study areas located throughout the range of the owl. A multi-state occupancy file was created by collapsing site-specific information on owl reproductive status into bimonthly (2 per month) survey occasions. These data were then analyzed to estimate annual reproductive rates, defined as: number of owls successfully reproducing/number of owl pairs, while accounting for variation in survey effort by accounting for imperfect detection of owls and potential misclassification of reproductive status. Covariates describing the probability of barred owl presence, habitat conditions, and climate were also included to explain variation in reproductive rates. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Data included here were analyzed and interpreted in the following manuscript in review: Rockweit, J. T. et al. 2021. Sources of Variation in Reproductive Rates of Northern Spotted Owls Across Their Range: A Prospective Meta-Analysis.The datasets associated with this readme file include all relevant script files needed for the multi-state occupancy analysis of northern spotted owl reproduction. For specific file information see the readme files in this record. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan

Estimating Northern Spotted Owl (\u3ci\u3eStrix occidentalis caurina\u3c/i\u3e) Pair Detection Probabilities Based on Call-Back Surveys Associated with Long-Term Mark-Recapture Studies, 1993–2018

The northern spotted owl (Strix occidentalis caurina; hereinafter NSO) was listed as “threatened” under the Endangered Species Act in 1990 and population declines have continued since that listing. Given the species’ protected status, any proposed activities on Federal lands that might impact NSO require consultation with U.S. Fish and Wildlife Service and part of that consultation often includes surveys to determine presence and occupancy status of the species in the proposed activity area. The objective of this report is to present study-area specific estimates of the probability of detection for NSO pairs from twelve 2-week seasonal survey periods using data from a recent range-wide meta-analysis. These estimates were a by-product of pair occupancy modeling but might provide insight into potential changes in the effect of the invasive barred owl on NSO detection rates. We used two-species multi-season occupancy models to estimate the probability of detection for NSOs on each of 11 study areas for each 2-week survey period and relative to the range-wide effect of barred owl presence or absence. Detection probabilities within the season generally increased from the earliest surveys in March through mid-season, decreasing again in the late season on five study areas. For three other study areas, detection rates were highest during the earliest survey periods in late March or early April. Estimates of cumulative seasonal detection of NSO (across a maximum of six within-season surveys) were less than 0.90 when barred owls (BO) were present on all but one study area, regardless of when surveys were conducted within a season. However, despite low detection rates, the probability that a territory was occupied when an NSO pair was not detected over six within-season surveys was also very low. When BO are not present on a territory, a six-survey protocol had a high probability of detecting an NSO pair at least once during the season on all study areas, except for the very lowest per-survey estimates. Conducting most surveys earlier in the season, when the probability of detecting pairs is highest (through May on most areas) could improve seasonal detection rates. However, alternative methods of population monitoring—such as the use of passive acoustic recorders—may be needed to continue monitoring NSO for research and management

Northern spotted owl reproductive rates (version 2)

These datasets were used in the prospective meta-analysis of northern spotted owl reproductive rates over 25 years across 11 study areas located throughout the range of the owl. A multi-state occupancy file was created by collapsing site-specific information on owl reproductive status into bimonthly (2 per month) survey occasions. These data were then analyzed to estimate annual reproductive rates, defined as: number of owls successfully reproducing/number of owl pairs, while accounting for variation in survey effort by accounting for imperfect detection of owls and potential misclassification of reproductive status. Covariates describing the probability of barred owl presence, habitat conditions, and climate were also included to explain variation in reproductive rates. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Data included here were analyzed and interpreted in the following manuscript in review: Rockweit, J. T. et al. 2021. Sources of Variation in Reproductive Rates of Northern Spotted Owls Across Their Range: A Prospective Meta-Analysis. The datasets associated with this readme file include all relevant script files needed for the multi-state occupancy analysis of northern spotted owl reproduction. For specific file information see the readme files in this record. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Version 2 has the same information as version 1, plus a table of ranked model results that includes all models tested and compared analyzing range-wide sources of variation in northern spotted owl reproductive rates

Northern spotted owl reproductive rates (version 3)

These datasets were used in the prospective meta-analysis of northern spotted owl reproductive rates over 25 years across 11 study areas located throughout the range of the owl. A multi-state occupancy file was created by collapsing site-specific information on owl reproductive status into bimonthly (2 per month) survey occasions. These data were then analyzed to estimate annual reproductive rates, defined as: number of owls successfully reproducing/number of owl pairs, while accounting for variation in survey effort by accounting for imperfect detection of owls and potential misclassification of reproductive status. Covariates describing the probability of barred owl presence, habitat conditions, and climate were also included to explain variation in reproductive rates. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Data included here were analyzed and interpreted in the following manuscript in review: Rockweit, J. T. et al. 2021. Sources of Variation in Reproductive Rates of Northern Spotted Owls Across Their Range: A Prospective Meta-Analysis. The datasets associated with this readme file include all relevant script files needed for the multi-state occupancy analysis of northern spotted owl reproduction. For specific file information see the readme files in this record. These data were collected as part of the long-term demographic monitoring of northern spotted owls in association with the Effectiveness Monitoring Plan of the Northwest Forest Plan. Version 2 has the same information as version 1, plus a table of ranked model results that includes all models tested and compared analyzing range-wide sources of variation in northern spotted owl reproductive rates.Version 2 has the same information as version 1, plus a table of ranked model results that includes all models tested and compared analyzing range-wide sources of variation in northern spotted owl reproductive rates.Version 3 has the same information as version 3, with the following changes: (1) Updated full list of models .csv to reflect updated analysis. (2) Updated the data files (.pao and seascov.csv) for the COA study area – all other study areas have not changed