Population Dynamics of Spotted Owls in the Sierra Nevada,California

ABSTRACT The California spotted owl (Strix occidentalis occidentalis) is the only spotted owl subspecies not listed as threatened or endangered under the United States Endangered Species Act despite petitions to list it as threatened. We conducted a meta-analysis of population data for 4 populations in the southem Cascades and Sierra Nevada, California, USA, from 1990 to 2005 to assist a listing evaluation by the United States Fish and Wildlife Service. Our study areas (from N to S) were on the Lassen National Forest (LAS), Eldorado National Forest (ELD), Sierra National Forest (SIE), and Sequoia and Kings Canyon National Parks (SKC). These study areas represented a broad spectrum of habitat and management conditions in these mountain ranges. We estimated apparent survival probability, reproductive output, and rate of population change for spotted owls on individual study areas and for all study areas combined (meta-analysis) using model selection or model-averaging based on maximum-likelihood estimation. We followed a formal protocol to conduct this analysis that was similar to other spotted owl meta-analyses. Consistency of field and analytical methods among our studies reduced confounding methodological effects when evaluating results. We used 991 marked spotted owls in the analysis of apparent survival. Apparent survival probability was higher for adult than for subadult owls. There was little difference in apparent survival between male and female owls. Model-averaged mean estimates of apparent survival probability of adult owls varied from 0.811 ± 0.021 for females at LAS to 0.890 ± 0.016 for males at SKC. Apparent survival increased over time for owls of all age classes at LAS and SIE, for adults at ELD, and for second-year subadults and adults at SKC. The meta-analysis of apparent survival, which included only adult owls, confirmed an increasing trend in survival over time. Survival rates were higher for owls on SKC than on the other study areas. We analyzed data from 1,865 observations of reproductive outcomes for female spotted owls. The proportion of subadult females among all territorial females of known age ranged from 0.00 to 0.25 among study areas and years. The proportion of subadults among female spotted owls was negatively related to reproductive output (no. of young fledged/territorial F owl) for ELD and SIE. Eldorado study area and LAS showed an alternate-year trend in reproductive output, with higher output in even-numbered years. Mean annual reproductive output was 0.988 ± 0.154 for ELD, 0.624 ± 0.140 for LAS, 0.478 ± 0.106 for SIE, and 0.555 ± 0.110 for SKC. Eldorado Study Area exhibited a declining trend and the greatest variation in reproductive output over time, whereas SIE and SKC, which had the lowest reproductive output, had the lowest temporal variation. Meta-analysis confirmed that reproductive output varied among study areas. Reproductive output was highest for adults, followed by second-year subadults, and then by first-year subadults. We used 842 marked subadult and adult owls to estimate population rate of change. Modeling indicated that Λ _t (Λ _t is the finite rate of population change estimated using the reparameterized Jolly–Seber estimator [Pradel 1996]) was either stationary (LAS and SIE) or increasing after an initial decrease (ELD and SKC). Mean estimated Λ _t for the 4 study areas was 1.007 (95% CI = 0.952–1.066) for ELD; 0.973 (95% CI = 0.946–1.001) for LAS; 0.992 (95% CI = 0.966–1.018) for SIE; and 1.006 (95% CI = 0.947–1.068) for SKC. The best meta-analysis model of population trend indicated that Λ varied across time but was similar in trend among the study areas. Our estimates of realized population change (Δ _t ; Franklin et al. 2004), which we estimated as the product 1 λ₃, were based on estimates of Λ _t from individual study areas and did not require estimating annual population size for each study area. Trends represented the proportion of the population size in the first year that remained in each subsequent year. Similar to λ₄ on which they were based, these λ_k-1 showed evidence of decline over the study period for LAS and SIE. The best model indicated recruitment of male and female adult and subadults varied from 0.10 to 0.31 new territorial individuals at time t/number of territorial individuals at time t–1 and similarly among areas. We also conducted a population viability analysis (PVA) based on results of our meta-analysis. This PVA was of limited utility for ELD and SKC study areas because 95% confidence intervals on the probability of decline or increase spanned the interval [0, 1] within 5–10 years. When we restricted inferences to 7 years, estimated probability of a >10% decline for SIE was 0.41 (95% CI = 0.09–0.78); for LAS the probability was 0.64 (95% CI = 0.27–0.94). In contrast, estimated probability of a >10% increase in 7 years for SIE was 0.23 (95% CI = 0.01–0.55) and for LAS was 0.10 (95% CI = 0.00–0.34). For comparisons, we simulated a PVA for a hypothetical population with mean Λ = 1.0 and the same temporal variation as observed in our owl populations. Our PVA suggested that both the SIE and LAS populations had higher probabilities of declining in a 7-year period than increasing but that it would be difficult to determine if a population was in a slight gradual decline. Our analysis and the repository of information on our 4 study populations provide a data-rich template for managers to monitor impacts of future management actions on the owl. Specifically, our data can be used to evaluate the effect of management strategies on spotted owls that are being implemented by the United States Forest Service to reduce the risk of wildfire in the Sierra Nevada ecosystem. Our information also provides baseline information for evaluating the status of the owl for potential listing as a threatened species by the United States Fish and Wildlife Service. RESUMEN El búho californiano manchado (Strix occidentalis occidentalis) es la única subespecie de búhos manchados que no está listada como amenazada o en peligro de extinción en el Acta de E.E.U.U. para las Especies en Peligro de Extinción a pesar de las peticiones para que sea incluida en la lista como una especie amenazada. Nosotros realizamos un meta-análisis de los datos de la población de 4 poblaciones del sur de Cascades y de la Sierra Nevada, California desde 1990 hasta 2005 como ayuda a una evaluación de listado hecha por el U.S Fish and Wildlife Service. Nuestras áreas de estudio (de norte a sur) estuvieron localizadas en el Bosque Nacional Lassen (LAS), en el Bosque Nacional Eldorado (ELD), en el Bosque Nacional Sierra (SIE) y en los Parques Nacionales Sequoia y Kings Canyon (SKC). Estas áreas de estudio representaron un amplio espectro del hábitat y de las condiciones de manejo en estas cadenas de montañas. Nosotros calculamos la probabilidad de supervivencia aparente, el volumen de reproducción y el cambio en la tasa de población de los búhos manchados en áreas de estudio individuales y para todas las áreas de estudio combinadas (meta-análisis) utilizando selección de modelos o promediando modelos basados en la estimación de máxima probabilidad. Seguimos un protocolo formal para realizar este análisis que fuera similar a otros meta-análisis con búhos manchados. La consistencia del campo y los métodos analíiticos en nuestros estudios redujeron la confusión de efectos metodológicos al evaluar los resultados. Utilizamos 991 búhos manchados marcados en el análisis de supervivencia aparente. La probabilidad de supervivencia aparente fue más alta para búhos adultos que para subadultos. Hubo poca diferencia en la supervivencia aparente entre hembras y machos. Para los modelos promediados, los cálculos de la media de la probabilidad de supervivencia aparente para búhos adultos tuvo una variación de 0.811 ± 0.021 para hembras en LAS a 0.890 ± 0.016 para machos en SKA. La supervivencia aparente aumentó con el tiempo para los búhos de todos los grupos de edad en LAS y SIE, para adultos en ELD, y para subadultos del segundo año y para adultos en SKC. El meta-análisis de supervivencia aparente, que incluyó únicamente a búhos adultos, confirmó una tendencia al aumento en la supervivencia con el tiempo. Las tasas de supervivencia fueron más altas para los búhos en SKC que en las otras áreas de estudio. Analizamos información de 1.865 observaciones de resultados de reproducciones para búhos manchados hembra. La proporción de hembras subadultas entre todas las hembras territoriales de edad conocida fluctuó de 0.00 a 0.25 a través de las áreas de estudio y de los años. La proporción de subadultos entre los búhos manchados hembra estuvo relacionada negativamente con el volumen de reproducción (número de pichones emplumados por búho hembra territorial) para ELD y SIE. ELD y LAS mostraron una tendencia anual alternada en el volumen de reproducción, con un volumen mayor en los años pares. La media del volumen de reproducción anual fue 0.988 ± 0.154 para ELD, 0.624 ± 0.140 para LAS, 0.478 ± 0.106 para SIE y 0.555 ± 0.154 para SKC. ELD exhibió una tendencia a disminuir y la variación más alta en el volumen de reproducción a través del tiempo; mientras que SIE y SKC, que tuvieron el más bajo volumen de reproducción, tuvieron la menor variación temporal. El meta-análisis confirmó que el volumen de reproducción varió entre las áreas de estudio. El volumen de reproducción fue más alto para adultos, seguido por subadultos del segundo año, y luego por subadultos del primer año. Nosotros utilizamos 842 búhos marcados, adultos y subadultos, para calcular el índice de cambio de la población. La selección de modelos indicó que Λ _t era, o relativamente fija (LAS y SIE) o aumentaba después de una disminución inicial (ELD y SKC). La media calculada Λ _t para las cuatro áreas de estudio fue: 1.007 (95% CI = 0.952–1.066) para ELD; 0.973 (95% CI = 0.946–1.001) para LAS; 0.992 (95% CI = 0.966–1.018) para SIE; y 1.006 (95% CI = 0.947–1.068) para SKC. El mejor modelo de meta-análisis de la tendencia de población indicó que Λ variaba con el tiempo pero que era una tendencia similar entre las áreas de estudio. Nuestros cálculos sobre el cambio de población realizado (Δ _t ) se basaron en los cálculos de Λ _t de las áreas de estudio individuales y no requirieron calcular el tamaño de la población anual para cada área de estudio. Las tendencias representaron la proporción del tamaño de la población en el primer año que permaneció en cada año subsiguiente. De manera similar a λ_t, en la que se basaron, éstas Δ_t mostraron evidencia de disminución durante el período de estudio para LAS y SIE. El mejor modelo de reclutamiento indicado, el reclutamiento de búhos machos y hembras, adultos y subadultos, varió de 0.10 a 0.31 individuos territoriales nuevos al tiempo t por el número de individuos territoriales al tiempo t–1 y de manera similar entre las otras áreas. También realizamos un análisis de viabilidad de población (PVA) basado en los resultados de nuestro meta-análisis. Este análisis PVA fue de limitada utilidad para las áreas de estudio ELD y SKC porque el 95% de intervalos de confiabilidad en la probabilidad de disminución o aumento extendió el intervalo [0, 1] de 5–10 años. Cuando restringimos las inferencias a 7 años, la probabilidad estimada de a >10% de disminución para SIE fue 0.41 (95% CI = 0.09–0.78); para LAS la probabilidad fue 0.64 (95% CI = 0.27–0.94). En contraste, la probabilidad estimada de un >10% de aumento en 7 años para SIE fue 0.23 (95% CI = 0.01–0.55) y para LAS fue 0.10 (95% CI = 0.00–0.34). Para comparar, simulamos un PVA para una población hipotética con una media Λ = 1.0, y con la misma variación temporal observada en nuestras poblaciones de búhos. Nuestro PVA sugirió que ambas poblaciones SIE y LAS tenían, en un período de 7 años, mayores probabilidades de disminución que de aumento, pero que sería muy difícil determinar si alguna de las poblaciones estaba en una ligera disminución gradual. El depósito de información de nuestras 4 áreas de estudio provee una plantilla rica en información para que los administradores monitoreen los impactos de acciones futuras en el manejo de los búhos (por ejemplo, nuevas estrategias de manejo del Plan de Sierra Nevada Forest). También provee evidencia importante para evaluar el estatus del búho para su potencial inclusión en el listado de especies amenazadas. RÉSUMÉ Le hibou tacheté californien (Strix occidentalis occidentalis) est la seule sous-espèce de hibou tacheté ne figurant pas sur la liste des animaux menacés ou vulnérables sous la Loi des Espèces en Danger des Etats-Unis malgré des pétitions pour l'inscrire sur cette liste en tant que sous-espèce menacée. Nous avons effectué une méta-analyse des données de population pour 4 populations dans le sud des Cascades et dans la Sierra Nevada, en Californie de 1990 à 2005 pour aider une évaluation de leur statut établie par les Services des Eaux et Forêts des Etats-Unis. Nos aires d'étude (du nord au sud) étaient dans la forêt nationale Lassen (LAS), la forêt nationale Eldorado (ELD), la forêt nationale Sierra (SIE), et les parcs nationaux Sequoia et Kings Canyon (SKC). Ces aires d'étude représentaient un large échantillon des conditions de l'habitat et de la gestion dans ces chaînes de montagnes. Nous avons estimé la probabilité de survie apparente, le succès de reproduction, et le taux de changement de la population pour les hiboux tachetés dans chaque aire d'étude individuelle et dans toutes les aires réunies (méta–analyse) en utilisant la sélection de modèles ou le calcul de la moyenne des modèles basé sur une estimation du maximum de vraisemblance. Pour effectuer cette analyse nous avons suivi un protocole rigoureux similaire à d'autres méta-analyses de hiboux tachetés. La cohérence des observations de terrain et des méthodes analytiques entre ces études a réduit les effets méthodologiques confondants lors des évaluations des résultats. Nous avons utilisé 991 hiboux tachetés marqués dans l'analyse de survie apparente. La probabilité de survie apparente a été plus élevée pour les hiboux adultes que pour les sous-adultes. Il y a eu peu de différence pour ce qui est de la survie apparente entre les hiboux mâles et femelles. La moyenne des estimations de la probabilité de survie apparente des hiboux adultes basée sur la moyenne des modèles a varié entre 0,811 ± 0,021 pour les hiboux femelles à LAS et 0,890 ± 0,016 pour les hiboux mâles à SKC. La survie apparente a augmenté avec le temps pour les hiboux de toutes les classes d'âge à LAS et SIE, pour les adultes à ELD, et pour les sous-adultes de deux ans et les adultes à SKC. La méta-analyse de survie apparente, qui comprenait seulement des hiboux adultes, a confirmé une tendance croissante de survie avec le temps. Les taux de survie étaient plus élevés pour les hiboux de SKC que pour ceux des autres aires d'étude. Nous avons analysé les données obtenues à partir de 1 865 observations de succès de reproduction de hiboux tachetées femelles. La proportion des hiboux femelles sous-adultes parmi toutes les femelles territoriales d'àge connu a varié de 0,00 à 0,25 selon les aires et les années d'étude. La proportion des sousadultes parmi les hiboux tachetés femelles a été négativement corrélée avec le succès de reproduction (nombre de jeunes hiboux par femelle territoriale) pour ELD et SIE. La forêt nationale Eldorado et la forêt nationale Lassen ont montré une tendance à alterner selon un cycle biennal pour ce qui est du succès de reproduction, avec un taux plus élevé pendant les années paires. La moyenne du succès de reproduction annuel était de 0,988 ± 0,154 pour ELD, de 0,624 ± 0,140 pour LAS, de 0,478 ± 0,106 pour SIE, et de 0,555 ± 0,110 pour SKD. La forêt nationale Eldorado a montré une tendance décroissante ainsi que la plus grande variation dans le succès de reproduction avec le temps, alors que SIE et SKC, qui ont eu le succès de reproduction le plus bas, ont connu la variation temporelle la plus basse. La méta-analyse a confirmé que le succès de reproduction variait selon les aires d'étude. Le succès de reproduction a été le plus élevé pour les adultes, puis pour les sous-adultes de deux ans, et ensuite pour les sous-adultes d'un an. Nous avons utilisé 842 hiboux marqués, adultes et sous-adultes, pour estimer le taux de changement de la population. La modélisation a indiqué que Λ _t était soit stationnaire (LAS et SIE), soit croissant après une baisse initiale (ELD et SKC). La moyenne estimée Λ _t pour les 4 aires d'étude était: 1,007 (95% IC = 0,952–1,066) pour ELD; 0,973 (95% IC = 0,946–1,001) pour LAS; 0,992 (95% IC = 0,966–1,018) pour SIE; et 1,006 (95% IC = 0,947–1,068) pour SKC. Le meilleur modèle de méta-analyse pour la tendance de la population a indiqué que Λ variait selon le temps mais suivait la même tendance selon les aires d'étude. Nos estimations du changement de population réalisé (Δ _t ) étaient fondées sur les estimations de Λ _t des aires d'étude individuelles et n'ont pas nécessité d'estimation de la taille annuelle de la population pour chaque aire d'étude. Les tendances représentaient la proportion de la taille de la population pendant la première année qui s'est maintenue chaque année subséquente. De même que λ_t sur lesquels ils étaient fondés, ces δ_t ont apporté des preuves de déclin pendant la période d'étude pour LAS et SIE. Le meilleur modèle a indiqué que le recrutement des hiboux adultes et sous-adultes mâles et femelles variait de 0,10 à 0,31 nouveaux individus territoriaux à un temps t pour un nombre d'individus territoriaux à un temps t-1 et qu'il en était de même dans chaque aire. Nous avons également procédé à une analyse de viabilité de la population (AVP) fondée sur les résultats de notre méta-analyse. Cette AVP a été d'une utilité limitée pour les aires d'étude ELD et SKC parce que les intervalles de confiance de 95% sur la probabilité du déclin ou de la croissance couvraient l'intervalle [0, 1] sur une période de 5 à 10 ans. Lorsque nous avons réduit les inférences à 7 ans, la probabilité estimée d'un déclin >10% pour SIE était de 0,41 (95% IC = 0,09–0,78); pour LAS la probabilité était de 0,64 (95% IC = 0,27–0,94). Al'opposé, la probabilité estimée d'une croissance >10% en 7 ans pour SIE était de 0,23 (95% IC = 0,01–0,55) et pour LAS elle était de 0,10 (95% IC = 0,00–0,34). Afin de comparer, nous avons simulé une AVP pour une population hypothétique ayant une moyenne Λ = 1,0 et la même variation temporelle que celle observée dans nos populations de hiboux. Notre AVP a suggéré que les populations de SIE et de LAS avaient de plus grandes probabilités de déclin que de croissance sur une période de 7 ans, mais qu'il serait difficile de déterminer si une population présentait un léger déclin graduel. La collecte des informations pour nos 4 aires d'étude foumit aux personnes chargées de la gestion un modèle riche de données permettant de suivre l'impact sur les hiboux des actions de gestion à l'avenir (par exemple, les nouvelles stratégies de gestion du Plan pour la Forêt de Sierra Nevada). Cette collecte foumit également des preuves importantes afin d'évaluer le statut du hibou pour une classification potentielle sur la liste des espèces menacées.     

Barred Owl Space Use and Habitat Selection in the Eastern Cascades,Washington

ABSTRACT Competition with barred owls (Strix varia varia) is an important factor contributing to the continued decline of threatened northern spotted owl (Strix occidentalis caurina) populations in the Pacific Northwest, USA, but basic information on habitat selection and space use patterns of barred owls is lacking for much of the region. We investigated space use and habitat selection by tracking radiotagged barred owls in the Eastern Cascade Range of Washington, USA, from 2004 to 2006. We surveyed for barred owls across the 309-km² study area and confirmed presence of barred owl pairs at 21 sites. We collected movement data on 14 barred owls from 12 sites. Mean annual 95% fixed-kernel home-range size was 194 ha for females (n = 4, SD = 70) and 288 ha for males (n = 5, SD = 114). Home ranges were located more frequently than expected in areas with low topographic position, gentle slopes, large overstory tree-crown diameter, high normalized difference vegetation index (NDVI), overstory tree canopy closure >72%, and a moderate amount of solar insolation. Within home ranges, areas that had large tree-crown diameters, low topographic positions, and gentle slopes were used more frequently than expected. The resource selection function we developed for barred owls in our study area indicated that barred owls used areas with the combination of low values for topographic position and slope and higher values for NDVI, solar insolation, and an interaction term for canopy closure and tree-crown diameter. In comparison to published information on northern spotted owls, barred owls used areas with similar canopy closure and tree size classes, but barred owl home ranges were much smaller and more concentrated on gentler slopes in valley bottoms. This information may contribute to the development of management practices that maintain forest characteristics appropriate for spotted owl habitat and prey in areas where spotted owls are least likely to be excluded by territorial barred owls in the Eastern Cascades of Washington.     

Home range and habitat selection of spotted owls in the central Sierra Nevada

We studied home range and habitat selection of radio-marked adult California spotted owls (Strix occidentalis occidentalis) randomly selected from among the breeding population of owls in the central Sierra Nevada, California from June to October 2006. The most parsimonious home-range estimate for our data was 555 ha (SE = 100 ha). Home-range size was positively correlated with the number of vegetation patches in the home range (habitat heterogeneity). We used resource selection ratios to examine selection of vegetation types by owls within our study area. Owl home ranges contained a high proportion of mature conifer forest, relative to its availability, although the confidence interval for this estimate overlapped one. We also used resource selection functions (RSF) to examine owl foraging habitat selection. Relative probability of selection of foraging habitat was correlated with vegetation classes, patch size, and their interaction. Owls showed highest selection rates for large patches (>10 ha) of pole-sized coniferous forest. Our results suggested that spotted owls in the central Sierra Nevada used habitat that contained a high proportion of mature conifer forest at the home-range scale, but at a finer scale (foraging site selection) owls used other vegetation classes interspersed among mature forest patches, consistent with our hypothesis that spotted owls may use other forest types besides old growth and mature forests when foraging. Our study provides an unbiased estimate of habitat use by spotted owls in the central Sierra Nevada. Our results suggest that forest managers continue to protect remaining mature and old-growth forests in the central Sierra Nevada because owl home ranges contain high proportions of these habitats. However, our results also showed that owls used younger stands as foraging habitat so that landscape heterogeneity, with respect to cover types, may be an important consideration for management but we did not attempt to relate our findings to fitness of owls. Thus management for some level of landscape heterogeneity for the benefit of owls should proceed with caution or under an adaptive management framework. © 2011 The Wildlife Society.     

Habitat selection by northern spotted owls in mixed-coniferous forests

Conservation planning for the federally threatened northern spotted owl (Strix occidentalis caurina) requires an ability to predict their responses to existing and future habitat conditions. To inform such planning we modeled habitat selection by northern spotted owls based upon fine-scale (approx. 1.0 ha) characteristics within stands comprised primarily of mixed-aged, mixed coniferous forests of southwestern Oregon and north-central California. We sampled nocturnal (i.e., primarily foraging) habitat use by 71 radio-tagged spotted owls over 5 yr in 3 study areas and sampled vegetative and physical environmental conditions at inventory plots within 95% utilization distributions of each bird. We compared conditions at available forest patches, represented by the inventory plots, with those at patches used by owls using discrete-choice regressions, the coefficients from which were used to construct exponential resource selection functions (RSFs) for each study area and for all 3 areas combined. Cross-validation testing indicated that the combined RSF was reasonably robust to local variation in habitat availability. The relative probability that a fine-scale patch was selected decreased nonlinearly with distances from nests and streams; varied unimodally with increasing average diameter of coniferous trees and also with increasing basal area of Douglas-fir (Pseudotsuga menziesii) trees; increased linearly with increasing basal areas of sugar pine (Pinus lambertiana) and hardwood trees and with increasing density of understory shrubs. Large-diameter trees (>66 cm) appeared important <400 m from nest sites. The RSF can support comparative risk assessments of the short- versus long-term effects of silvicultural alternatives designed to integrate forest ecosystem restoration and habitat improvement for northern spotted owls. Results suggest fine-scale factors may influence population fitness among spotted owls. © 2011 The Wildlife Society.     

Stable isotopes reveal unexpected relationships between fire history and the diet of Spotted Owls

Although the effects of shifting fire regimes on bird populations have been recognized as important to ecology and conservation, the consequences of fire for trophic interactions of avian species – and raptors in particular – remain relatively unknown. Here, we found that within national parks with long‐standing (40+ years) fire management programmes, California Spotted Owls Strix occidentalis occidentalis consumed predominantly Woodrats Neotoma spp. and Pocket Gophers Thomomys spp.; however, in contrast to our predictions, when their territories experienced more extensive and frequent fire, Spotted Owls consumed proportionally more Flying Squirrels Glaucomys oregonensis. We hypothesize this finding could have been driven by either changes to prey abundance following fires (e.g. increases in flying squirrels) or changes to prey availability (e.g. shifts in forest structure or flying squirrel spatial distribution that increased predation upon them by owls). Our work thus demonstrates that fire may have unexpected consequences for the trophic interactions of raptor species and provides valuable information for the conservation of Spotted Owls in fire‐prone forest landscapes.     

Population decline in California spotted owls near their southern range boundary

Species worldwide have begun to shift their range boundaries in response to climate change and other anthropogenic causes, with population declines at the trailing edge of a species' range often foreshadowing future changes in core parts of the range. Therefore, we analyzed a 30-year (1991–2019) data set for the California spotted owl (Strix occidentalis occidentalis) near its southern range boundary in southern California, USA, that included the largest regional population (San Bernardino Mountains) to estimate trends in territory occupancy and reproduction. We then assessed how these demographic rates were affected by habitat, wildfire, fuel treatments, and climate. Mean occupancy declined from 0.82 to 0.39 during our study, whereas reproductive output showed no temporal trends ( young/occupied territory). Territory extinction (extirpation) rates were relatively low in territories with more large trees (≥50 cm dbh), and colonization increased strongly with large tree density for low-elevation territories within the shrub-woodland ecotype but not for higher-elevation territories within mixed-conifer forest. High-severity wildfire had an adverse effect on occupancy: territory extinction rates steadily increased with the amount of high-severity fire within an owl territory during the previous 10 years, while colonization declined to nearly zero when ≥40% of a territory burned at high-severity during the previous 10 years. The effects of high-severity fire were unlikely to be confounded with post-fire fuel treatments, which primarily consisted of the removal, burning, or scattering of brush and small trees and snags (<40.6 cm dbh) and affected much smaller areas than high-severity fire. Of the 40 territories that received fuel treatments within 10 years of a fire, only 3 of them had post-fire fuel treatments that affected >5% of the territory, whereas average area burned at high severity for all 40 territories was 17%. Fuel treatments intended to modify fire behavior and reduce the likelihood of large, high-severity fires led to increases in territory extinction and colonization such that their net effect on occupancy was minimal. Our simulations of occupancy dynamics indicated that high-severity fire accounted for 9.6% of the observed decline in occupancy, whereas fuel treatments effectively accounted for none of the decline. Spotted owl reproductive output was lower at territories where fuel treatments occurred, but low- to moderate-severity fire resulted in much larger, population-level reductions in reproductive output (141 fewer young) from 2006–2019 than treatments (19 fewer young). Thus, the benefits of fuel treatments that reduce fire occurrence and severity appear to outweigh potential short-term costs to spotted owls and their habitat. Because high-severity fire only explained a modest amount of the long-term occupancy decline and much of the decline occurred in the 1990s before large fires occurred, additional factors are likely adversely affecting the owl population and merit further study. Nevertheless, the large observed population decline, limited evidence of owl dispersal among mountain ranges in the southern California metapopulation, and negative effects of increasingly large and severe fire suggest that California spotted owls at their southern range boundary are vulnerable to extirpation. In an era of climate change, owls in the core part of the range will likely become increasingly susceptible to warmer temperatures and increased severe fire activity in the future. Thus, the restoration of historical, low-severity fire regimes through fuels management while maintaining large trees is important to improving owl persistence.     

Habitat Selection by American Martens in Coastal California

ABSTRACT We investigated habitat selection using single- and mixed-scale modeling at 2 spatial scales, stand and home range, by the only known population of American martens (Martes americana) remaining in the historical range of the Humboldt subspecies (M. a. humboldtensis) in California, USA. During 2000 and 2001, we sampled a 12 times 14 grid with 2-km spacing, using 2 sooted track plates at each grid point. We detected martens at 26 of the 159 grid points. We used resource selection probability functions and an information-theoretic method to model habitat at detection locations. At the stand scale, martens selected conifer-dominated stands with dense, spatially extensive shrub cover (x̄ = 74% cover, SE = 4) in the oldest developmental stage. At the home-range scale, martens selected the largest available patches (x̄ = 181 ha, SE = 14) of old-growth, old-growth and late-mature, or serpentine habitat. Mixed-scale models revealed that habitat characteristics from both scales best explained marten occurrence compared to one scale alone. Dense, spatially extensive shrub cover is a key habitat element for martens in coastal forests. Dense shrubs provide refuge from predators, cover for prey, and may also deter larger-bodied competitors. Managers can increase the likelihood of marten population persistence and encourage expansion in coastal forests by maintaining and restoring late-mature and old-growth, conifer-dominated forests with dense shrub cover in large, contiguous patches.     

Quantitative Evidence for Increasing Forest Fire Severity in the Sierra Nevada and Southern Cascade Mountains, California and Nevada, USA

Recent research has concluded that forest wildfires in the western United States are becoming larger and more frequent. A more significant question may be whether the ecosystem impacts of wildfire are also increasing. We show that a large area (approximately 120000 km²) of California and western Nevada experienced a notable increase in the extent of forest stand-replacing (“high severity”) fire between 1984 and 2006. High severity forest fire is closely linked to forest fragmentation, wildlife habitat availability, erosion rates and sedimentation, post-fire seedling recruitment, carbon sequestration, and various other ecosystem properties and processes. Mean and maximum fire size, and the area burned annually have also all risen substantially since the beginning of the 1980s, and are now at or above values from the decades preceding the 1940s, when fire suppression became national policy. These trends are occurring in concert with a regional rise in temperature and a long-term increase in annual precipitation. A close examination of the climate–fire relationship and other evidence suggests that forest fuels are no longer limiting fire occurrence and behavior across much of the study region. We conclude that current trends in forest fire severity necessitate a re-examination of the implications of all-out fire suppression and its ecological impacts. Author Contributions: Jay Miller designed the study, performed research, analyzed data, and wrote the article. Hugh Safford performed research, analyzed data, and wrote the article. Michael Crimmins performed research and analyzed data. Andi Thode designed the study and performed research.     

Comparative Space Use and Habitat Selection of Moose Around Feeding Stations

ABSTRACT The practice of feeding cervids in winter, either as a supplement to enhance nutritional status or to divert animals away from roads, railways, or vulnerable habitats, is rising noticeably. Moose (Alces alces) densities in Scandinavia are currently at historically high levels, resulting in amplified damage to economically important young Scots pine (Pinus sylvestris) forest stands. Nevertheless, there is limited information as to how diversionary feeding affects herbivore space use and habitat selection. We followed 32 female moose marked with Global Positioning System collars to evaluate 1) if feeding stations serve as attraction points to the extent that habitat-selection patterns resemble those of central-place foragers (i.e., high usage and more uniform selection close to the attraction point), and 2) if moose using feeding sites select young pine stands less than those not using feeding sites. Moose that used diversionary forage concentrated their space use around feeding stations and selected habitats as predicted for a central-place forager with a decreasing probability of using areas away from feeding sites and a low degree of habitat selectivity close to feeding sites. However, moose that used feeding sites continued to select young pine stands to the same extent as moose that did not use feeding sites. Feeding sites were, therefore, not successful in diverting moose away from valuable natural browse, so we recommend wildlife managers establish feeding sites in sacrifice areas where moose browsing is permissible and, if possible, >1 km from young pine plantations.     

Multiscale Habitat Selection by Burrowing Owls in Black-Tailed Prairie Dog Colonies

ABSTRACT Some populations of western burrowing owls (Athene cunicularia hypugaea) have declined in recent decades. To design and implement effective recovery efforts, we need a better understanding of how distribution and demographic traits are influenced by habitat quality. To this end, we measured spatial patterns of burrowing owl breeding habitat selection within black-tailed prairie dog (Cynomys ludovicianus) colonies in northeastern Wyoming, USA. We compared burrow-, site-, colony-, and landscape-scale habitat parameters between burrowing owl nest burrows (n = 105) and unoccupied burrows (n = 85). We sampled 4 types of prairie dog colonies: 1) owl-occupied, active with prairie dogs (n = 16); 2) owl-occupied, inactive (n = 13); 3) owl-unoccupied, active (n = 14); and 4) owl-unoccupied, inactive (n = 14). We used an information-theoretic approach to examine a set of candidate models of burrowing owl nest-site selection. The model with the most support included variables at all 4 spatial scales, and results were consistent among the 4 types of prairie dog colonies. Nest burrows had longer tunnels, more available burrows within 30 m, and less shrub cover within 30 m, more prairie dog activity within 100 m, and were closer to water than unoccupied burrows. The model correctly classified 76% of cases, all model coefficients were stable, and the model had high predictive ability. Based on our results, we recommend actions to ensure persistence of the remaining prairie dog colonies as an important management strategy for burrowing owl conservation in the Great Plains of North America.     

Genetic differentiation and inferred dynamics of a hybrid zone between Northern Spotted Owls (Strix occidentalis caurina) and California Spotted Owls (S. o. occidentalis) in northern California

Genetic differentiation among Spotted Owl (Strix occidentalis) subspecies has been established in prior studies. These investigations also provided evidence for introgression and hybridization among taxa but were limited by a lack of samples from geographic regions where subspecies came into close contact. We analyzed new sets of samples from Northern Spotted Owls (NSO: S. o. caurina) and California Spotted Owls (CSO: S. o. occidentalis) in northern California using mitochondrial DNA sequences (mtDNA) and 10 nuclear microsatellite loci to obtain a clearer depiction of genetic differentiation and hybridization in the region. Our analyses revealed that a NSO population close to the northern edge of the CSO range in northern California (the NSO Contact Zone population) is highly differentiated relative to other NSO populations throughout the remainder of their range. Phylogenetic analyses identified a unique lineage of mtDNA in the NSO Contact Zone, and Bayesian clustering analyses of the microsatellite data identified the Contact Zone as a third distinct population that is differentiated from CSO and NSO found in the remainder of the subspecies' range. Hybridization between NSO and CSO was readily detected in the NSO Contact Zone, with over 50% of individuals showing evidence of hybrid ancestry. Hybridization was also identified among 14% of CSO samples, which were dispersed across the subspecies' range in the Sierra Nevada Mountains. The asymmetry of hybridization suggested that the hybrid zone may be dynamic and moving. Although evidence of hybridization existed, we identified no F1 generation hybrid individuals. We instead found evidence for F2 or backcrossed individuals among our samples. The absence of F1 hybrids may indicate that (1) our 10 microsatellites were unable to distinguish hybrid types, (2) primary interactions between subspecies are occurring elsewhere on the landscape, or (3) dispersal between the subspecies' ranges is reduced relative to historical levels, potentially as a consequence of recent regional fires.     

Space Use and Habitat Selection by Bobcats in the Fragmented Landscape of South-Central Iowa

Abstract: Historically, bobcats (Lynx rufus) were found throughout the Corn Belt region, but they nearly disappeared from this area due to habitat loss and unregulated harvest that occurred during the century after European settlement. Reports of bobcat occurrences have been increasing in Iowa, USA, and biologists would like to understand the mechanisms enabling bobcats to recolonize this fragmented agricultural landscape. We determined space use and habitat selection of bobcats by radiocollaring 68 bobcats in south-central Iowa during 2003–2006. We triangulated 12,966 locations and recovered an additional 1,399 3-dimensional locations from Global Positioning System collars. We used a fixed kernel estimator to calculate 95% utilization distributions (UDs) for home ranges and 50% UDs for cores. Annual home range area of males (x̄ = 58.6 km², 95% CI = 49.2–69.9) was nearly 3 times that of females (x̄=19.9 km², 95% CI = 17.0–23.3). Females used smaller home ranges during April-September when they were suspected to have kittens with them (x̄ = 16.8 km², 95% CI = 13.7–20.7), as compared to October-March (x̄ = 24.1 km², 95% CI = 19.0–30.7), whereas home ranges of males did not differ between seasons. Similarly, core area of males (x̄ = 7.7 km², 95% CI = 6.2–9.6) was larger than that of females (x̄ = 2.3 km², 95% CI = 1.9–2.7). Females used significantly smaller cores in April-September (x̄ = 1.8 km², 95% CI = 1.4–2.3) as compared to October-March (x̄ = 2.8 km², 95% CI = 2.2–3.7), whereas males did not. For both sexes, compositional analysis indicated that forest habitat was ranked higher than all other habitat classes at both the landscape and local scale. Standardized habitat selection ratios illustrate that female and male bobcats selected forest habitat about twice as frequently as any other habitat class, including grassland and Conservation Reserve Program land. Predictive models indicated that home range and core area was smaller in landscapes where perennial forest and grassland habitats were less fragmented. Predictive models indicated home ranges were more irregular in shape in landscapes where row crop patches were less aggregated within home ranges. Our results have practical implications for wildlife managers regarding expected bobcat habitat use and distribution as the species becomes more abundant in the agricultural landscape of the Midwest.     

Habitat Selection of Female Turkeys in a Managed Pine Landscape in Mississippi

Abstract: Intensive pine (Pinus spp.) management is a dominant form of forest management in the southeastern United States. Previous research has shown that managed pine forests provide suitable habitat for eastern wild turkeys (Meleagris gallopavo silvestris), but little research has examined seasonal habitat selection for female wild turkeys from a landscape perspective, particularly within managed pine landscapes. Therefore, we used a long-term (1986-1993) data set to describe seasonal habitat selection by female wild turkeys, using an information-theoretic approach from a landscape perspective, on an intensively managed pine landscape. Habitat use patterns during preincubation and autumn-winter were indicative of female wild turkeys moving between a bottomland hardwood-agricultural field complex during autumn-winter and upland managed pine stands during the remainder of the year. During spring and summer, female wild turkeys used landscapes primarily composed of intensively managed pine, including thinned and burned stands and roadsides. Our results confirm results of short-term, stand-based habitat analyses on our study area. We recommend variable fire return intervals of 3 to 7 years to improve habitat conditions for wild turkeys within intensively managed pine forests. Further research is needed to examine management actions, such as thinning, prescribed fire, and herbicide use, within the context of wild turkey use of intensively managed pine landscapes.