Douglas J. Tempel

Relation between Occupancy and Abundance for a Territorial Species, the California Spotted Owl

Land and resource managers often use detection-nondetection surveys to monitor the populations of species that may be affected by factors such as habitat alteration, climate change, and biological invasions. Relative to mark-recapture studies, using detection-nondetection surveys is more cost-effective, and recent advances in statistical analyses allow the incorporation of detection probability, covariates, and multiple seasons. We examined the efficacy of using detection-nondetection data (relative to mark-recapture data) for monitoring population trends of a territorial species, the California Spotted Owl (Strix occidentalis occidentalis). We estimated and compared the finite annual rates of population change (λt ) and the resulting realized population change (Δt ) from both occupancy and mark-recapture data collected over 18 years (1993-2010). We used multiseason, robust-design occupancy models to estimate that territory occupancy declined during our study (Δt = 0.702, 95% CI 0.552-0.852) due to increasing territory extinction rates (ε(1993) = 0.019 [SE 0.012]; ε(2009) = 0.134 [SE 0.043]) and decreasing colonization rates (γ(1993) = 0.323 [SE 0.124]; γ(2009) = 0.242 [SE 0.058]). We used Pradels temporal-symmetry model for mark-recapture data to estimate that the population trajectory closely matched the trends in territory occupancy (Δt = 0.725, 95% CI 0.445-1.004). Individual survival was constant during our study (φ(1993) = 0.816 [SE 0.020]; φ(2009) = 0.815 [SE 0.019]), whereas recruitment declined slightly (f(1993) = 0.195 [SE 0.032]; f(2009) = 0.160 [SE 0.023]). Thus, we concluded that detection-nondetection data can provide reliable inferences on population trends, especially when funds preclude more intensive mark-recapture studies.

Evaluating short- and long-term impacts of fuels treatments and simulated wildfire on an old-forest species

Fuels-reduction treatments are commonly implemented in the western U.S. to reduce the risk of high-severity fire, but they may have negative short-term impacts on species associated with older forests. Therefore, we modeled the effects of a completed fuels-reduction project on fire behavior and California Spotted Owl (Strix occidentalis occidentalis) habitat and demography in the Sierra Nevada to assess the potential short- and long-term trade-offs. We combined field-collected vegetation data and LiDAR data to develop detailed maps of forest structure needed to parameterize our fire and forest-growth models. We simulated wildfires under extreme weather conditions (both with and without fuels treatments), then simulated forest growth 30 years into the future under four combinations of treatment and fire: treated with fire, untreated with fire, treated without fire, and untreated without fire. We compared spotted owl habitat and population parameters under the four scenarios using a habitat suitability index developed from canopy cover and large-tree measurements at nest sites and from previously derived statistical relationships between forest structure and fitness (k) and equilibrium occupancy at the territory scale. Treatments had a positive effect on owl nesting habitat and demographic rates up to 30 years after simulated fire, but they had a persistently negative effect throughout the 30-year period in the absence of fire. We conclude that fuels-reduction treatments in the Sierra Nevada may provide long-term benefits to spotted owls if fire occurs under extreme weather conditions, but can have long-term negative effects on owls if fire does not occur. However, we only simulated one fire under the treated and untreated scenarios and therefore had no measures of variation and uncertainty. In addition, the net benefits of fuels treatments on spotted owl habitat and demography depends on the future probability that fire will occur under similar weather and ignition conditions, and such probabilities remain difficult to quantify. Therefore, we recommend a landscape approach that restricts timber harvest within territory core areas of use (;125 ha in size) that contain critical owl nesting and roosting habitat and locates fuels treatments in the surrounding areas to reduce the potential for high-severity fire in territory core areas.

Effects of forest management on California Spotted Owls: implications for reducing wildfire risk in fire-prone forests

Management of many North American forests is challenged by the need to balance the potentially competing objectives of reducing risks posed by high-severity wildfires and protecting threatened species. In the Sierra Nevada, California, concern about high-severity fires has increased in recent decades but uncertainty exists over the effects of fuel-reduction treatments on species associated with older forests, such as the California Spotted Owl (Strix occidentalis occidentalis). Here, we assessed the effects of forest conditions, fuel reductions, and wildfire on a declining population of Spotted Owls in the central Sierra Nevada using 20 years of demographic data collected at 74 Spotted Owl territories. Adult survival and territory colonization probabilities were relatively high, while territory extinction probability was relatively low, especially in territories that had relatively large amounts of high canopy cover (≥70%) forest. Reproduction was negatively associated with the area of medium-intensity timber harvests characteristic of proposed fuel treatments. Our results also suggested that the amount of edge between older forests and shrub/sapling vegetation and increased habitat heterogeneity may positively influence demographic rates of Spotted Owls. Finally, high-severity fire negatively influenced the probability of territory colonization. Despite correlations between owl demographic rates and several habitat variables, life stage simulation (sensitivity) analyses indicated that the amount of forest with high canopy cover was the primary driver of population growth and equilibrium occupancy at the scale of individual territories. Greater than 90% of medium-intensity harvests converted high-canopy-cover forests into lower-canopy-cover vegetation classes, suggesting that landscape-scale fuel treatments in such stands could have short-term negative impacts on populations of California Spotted Owls. Moreover, high-canopy-cover forests declined by an average of 7.4% across territories during our study, suggesting that habitat loss could have contributed to declines in abundance and territory occupancy. We recommend that managers consider the existing amount and spatial distribution of high-canopy forest before implementing fuel treatments within an owl territory, and that treatments be accompanied by a rigorous monitoring program.

Estimating population impacts via dynamic occupancy analysis of Before—After Control—Impact studies

Estimating environmental impacts on populations is one of the main goals of wildlife monitoring programs, which are often conducted in conjunction with management actions or following natural disturbances. In this study we investigate the statistical power of dynamic occupancy models to detect changes in local survival and colonization from detection-nondetection data, while accounting for imperfect detection probability, in a Before-After Control-Impact (BACI) framework. We simulated impacts on local survival and/or detection probabilities, and asked questions related to: (1) costs and benefits of different analysis models, (2) confounding changes in detection with changes in local survival, (3) sampling design trade-offs, and (4) species with low vs. high rates of turnover. Estimating seasonal effects on local survival and colonization, as opposed to estimating Before-After effects, had little effect on the power to detect changes in local survival. Estimating a parameter that accounted for pretreatment differences in local survival between Control and Impact sites decreased power by 50%, but it was critical to include when such differences existed. When the experimental treatment had a negative impact on species detectability but analysis assumed constant detection, the Type I error rates were dramatically inflated (0.20 0.33). In general, there was low power (< 0.5) to detect a 50% decrease in local survival for all combinations of sites (N = 50 vs. 100), seasons sampled (8 vs. 12), and visits per site per season (4 vs. 6). Unbalanced designs performed worse than balanced designs, with the exception of the case of treatments being implemented in different seasons at different sites. Adding more control sites improved the ability to detect changes in local survival. Surveying more seasons after impact resulted in modest power gains, but at least three seasons before impact were required to successfully implement BACI occupancy studies. Turnover rates had a low impact on power. Occupancy studies conducted in a BACI design offer the opportunity to detect environmental impacts on wildlife populations without the costs of intensive studies. However, given the low power to detect small changes (20%) in local survival, these studies should be used when researchers are confident that major treatment impacts will occur or very large sample sizes are obtainable.

FACTORS RELATED TO FECAL ESTROGENS AND FECAL TESTOSTERONE IN CALIFORNIA SPOTTED OWLS

Abstract We estimated concentrations of fecal reproductive steroid metabolites in free-ranging California Spotted Owls (Strix occidentalis occidentalis) during the breeding season. We collected fresh fecal samples (n = 142) from 65 individual owls in the Sierra Nevada during April–August of 2001. We developed and validated radioimmunoassay procedures to quantify fecal estrogen metabolites and fecal testosterone metabolites. We used an information-theoretic approach to identify factors that might influence fecal estrogen (E), fecal testosterone (T), and fecal estrogen:testosterone ratio (E:T ratio) levels during the owls breeding season. We hypothesized that factors related to sampling procedures, owl characteristics (sex, reproductive status), and habitat might influence fecal reproductive steroid levels. Our analyses suggested that sampling factors and owl characteristics, but not habitat variables, were related to fecal reproductive steroid levels in Spotted Owls. Our most supported models explained <30% of the observed variation. Fecal testosterone levels were higher in male Spotted Owls than females, whereas E:T ratios were higher in females compared to males. High fecal estrogens were correlated with high fecal glucocorticoids in nonbreeding Spotted Owls, whereas fecal estrogens and fecal glucocorticoids were not related in breeding birds. Sampling influenced fecal reproductive steroid measures, and bias from small-mass fecal samples might partially explain these relationships. Noninvasive measurements of fecal reproductive steroids might be useful for sex determination and reproductive assessment of free-ranging Spotted Owls. However, more research is needed to understand the variability we observed in sex steroids before this technique can be effective in conservation studies. Factores Asociados con los Estrógenos Fecales y la Testosterona Fecal en Strix occidentalis occidentalis Resumen. Estimamos las concentraciones de metabolitos esteroides reproductivos en individuos silvestres de la especie Strix occidentalis occidentalis durante la época reproductiva. Colectamos muestras fecales frescas (n = 142) pertenecientes a 65 lechuzas en la Sierra Nevada entre abril y agosto de 2001. Desarrollamos y validamos un procedimiento de radioinmunoensayo para cuantificar metabolitos de estrógeno fecales y metabolitos de testosterona fecales. Utilizamos un enfoque informativo-teórico para identificar los factores que podrían influenciar los niveles de estrógenos fecales (E), testosterona fecal (T) y el cociente entre estrógenos y testosterona (cociente E:T) durante la época reproductiva de las lechuzas. Hipotetizamos que factores relacionados con los procedimientos de muestreo, características de la lechuza (sexo, estado reproductivo) y el hábitat podrían influenciar los niveles de esteroides reproductivos en las fecas. Nuestros análisis sugieren que los factores asociados al muestreo y las características de la lechuza se correlacionaron con los niveles de esteroides reproductivos en las fecas, pero éstos no se relacionaron con las variables de hábitat. Nuestro modelo más robusto explicó <30% de la variación observada. Los niveles de testosterona fecal fueron mayores en los machos que en las hembras, mientras que el cuociente E:T fue mayor en las hembras que en los machos. En lechuzas no reproductivas, los niveles altos de estrógenos fecales se correlacionaron con niveles altos de glucocorticoides fecales, mientras que en individuos reproductivos los estrógenos fecales y los glucorticoides fecales no se correlacionaron. Estas relaciones pueden ser explicadas en parte por la influencia del muestreo sobre las medidas de esteroides reproductivos fecales y por el sesgo causado por muestras fecales muy livianas. Los niveles de esteroides reproductivos fecales medidos con técnicas no invasivas pueden ser útiles para la determinación de sexos y la evaluación del estado reproductivo de individuos silvestres de la especie S. occidentalis occidentalis. Sin embargo, antes de que esta técnica pueda ser efectiva en estudios de conservación, se requiere de más investigación para entender la variabilidad que observamos en los niveles de esteroides sexuales.

Meta-analysis of California Spotted Owl (Strix occidentalis occidentalis) territory occupancy in the Sierra Nevada: Habitat associations and their implications for forest management

ABSTRACT We assessed the occupancy dynamics of 275 California Spotted Owl (Strix occidentalis occidentalis) territories in 4 study areas in the Sierra Nevada, California, USA, from 1993 to 2011. We used Landsat data to develop maps of canopy cover for each study area, which we then used to quantify annual territory-specific habitat covariates. We modeled the relationships between territory extinction and colonization using predictor variables of habitat, disturbance (logging, fire), climate, and elevation. We found that forests with medium (40–69%) and high (≥70%) canopy cover were the most important predictors of territory occupancy in all study areas, and that both canopy cover categories were positively correlated with occupancy. We used analysis of deviance to estimate the amount of variation explained by the habitat covariates (primarily medium and high canopy cover) and found that these covariates explained from 35% to 67% of the variation in occupancy. Climatic covariates were not correlated with occupancy dynamics and explained little of the variation in occupancy. We also conducted a post hoc analysis in which we partitioned canopy cover into 10% classes, because our original partitioning into 3 classes may have lacked sufficient resolution to identify canopy cover levels where occupancy changed abruptly. In this post hoc analysis, occupancy declined sharply when territories contained more area with <40% canopy cover, and the amount of 50–59% and 60–69% canopy cover had a more positive association with occupancy than did 40–49% canopy cover. Our results suggest that some fuels treatments intended to reduce fire risk and improve forest resilience could be located within Spotted Owl territories without adversely impacting territory occupancy if such treatments do not consistently reduce canopy cover below 50%. We suggest that future work quantify components of forest structure (e.g., large tree density, vertical complexity) known to be selected by owls and relate these characteristics to occupancy and fitness metrics.

Genomics meets applied ecology: Characterizing habitat quality for sloths in a tropical agro-ecosystem

Understanding how habitat quality in heterogeneous landscapes governs the distribution and fitness of individuals is a fundamental aspect of ecology. While mean individual fitness is generally considered a key to assessing habitat quality, a comprehensive understanding of habitat quality in heterogeneous landscapes requires estimates of dispersal rates among habitat types. The increasing accessibility of genomic approaches, combined with field‐based demographic methods, provides novel opportunities for incorporating dispersal estimation into assessments of habitat quality. In this study, we integrated genomic kinship approaches with field‐based estimates of fitness components and approximate Bayesian computation (ABC) procedures to estimate habitat‐specific dispersal rates and characterize habitat quality in two‐toed sloths (Choloepus hoffmanni) occurring in a Costa Rican agricultural ecosystem. Field‐based observations indicated that birth and survival rates were similar in a sparsely shaded cacao farm and adjacent cattle pasture–forest mosaic. Sloth density was threefold higher in pasture compared with cacao, whereas home range size and overlap were greater in cacao compared with pasture. Dispersal rates were similar between the two habitats, as estimated using ABC procedures applied to the spatial distribution of pairs of related individuals identified using 3,431 single nucleotide polymorphism and 11 microsatellite locus genotypes. Our results indicate that crops produced under a sparse overstorey can, in some cases, constitute lower‐quality habitat than pasture–forest mosaics for sloths, perhaps because of differences in food resources or predator communities. Finally, our study demonstrates that integrating field‐based demographic approaches with genomic methods can provide a powerful means for characterizing habitat quality for animal populations occurring in heterogeneous landscapes.