John J. Keane

Blood Parasites in Owls with Conservation Implications for the Spotted Owl (Strix occidentalis)

The three subspecies of Spotted Owl (Northern, Strix occidentalis caurina; California, S. o. occidentalis; and Mexican, S. o. lucida) are all threatened by habitat loss and range expansion of the Barred Owl (S. varia). An unaddressed threat is whether Barred Owls could be a source of novel strains of disease such as avian malaria (Plasmodium spp.) or other blood parasites potentially harmful for Spotted Owls. Although Barred Owls commonly harbor Plasmodium infections, these parasites have not been documented in the Spotted Owl. We screened 111 Spotted Owls, 44 Barred Owls, and 387 owls of nine other species for haemosporidian parasites (Leucocytozoon, Plasmodium, and Haemoproteus spp.). California Spotted Owls had the greatest number of simultaneous multi-species infections (44%). Additionally, sequencing results revealed that the Northern and California Spotted Owl subspecies together had the highest number of Leucocytozoon parasite lineages (n = 17) and unique lineages (n = 12). This high level of sequence diversity is significant because only one Leucocytozoon species (L. danilewskyi) has been accepted as valid among all owls, suggesting that L. danilewskyi is a cryptic species. Furthermore, a Plasmodium parasite was documented in a Northern Spotted Owl for the first time. West Coast Barred Owls had a lower prevalence of infection (15%) when compared to sympatric Spotted Owls (S. o. caurina 52%, S. o. occidentalis 79%) and Barred Owls from the historic range (61%). Consequently, Barred Owls on the West Coast may have a competitive advantage over the potentially immune compromised Spotted Owls.

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 southern 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 λt (λt 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 λt 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 (Δt; Franklin et al. 2004), which we estimated as the product 1 × λˆ3 × λˆ4 × …× λˆk−1, were based on estimates of λt 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 λˆt on which they were based, these Δˆt 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.

Temporal Variation in Resource Use by Black-Throated Gray Warblers

We studied foraging behavior and habitat use of male and female Black-throated Gray Warblers (Dendroica nigrescens) to quantify the effects of temporal variation on interpretations of avian resource use. Overall, both sexes primarily foraged by gleaning in single-leaf pinyon pine (Pinus monophyla); however, within-season and between-year variation in behavior and habitat use were found for both sexes. Warblers increased use of shrubs from May to mid-June, and decreased use of shrubs and increased use of pinyon pine from mid-June through August, during each year. Use of sagebrush (Artemisia tridentata) and Utah juniper (Juniper osteosperma) varied between years. Sex differences were found in proportional use of foraging maneuvers. Within-season shifts in plant species and habitat use corresponded to changes in arthropod numbers on the plant species used by the warblers, but between-year shifts in behavior did not correspond as closely with changes in arthropod numbers. Temporal variation in microhabitat use resulted from shifts within seasons in the plant species used for foraging, which was associated with temporal changes in food abundance. Our results also demonstrate the importance of considering the effects of temporal scale in studies of bird-resource interactions.

Range-wide genetic differentiation among North American great gray owls (Strix nebulosa) reveals a distinct lineage restricted to the Sierra Nevada, California.

Investigations of regional genetic differentiation are essential for describing phylogeographic patterns and informing management efforts for species of conservation concern. In this context, we investigated genetic diversity and evolutionary relationships among great gray owl (Strix nebulosa) populations in western North America, which includes an allopatric range in the southern Sierra Nevada in California. Based on a total dataset consisting of 30 nuclear microsatellite DNA loci and 1938-base pairs of mitochondrial DNA, we found that Pacific Northwest sampling groups were recovered by frequency and Bayesian analyses of microsatellite data and each population sampled, except for western Canada, showed evidence of recent population bottlenecks and low effective sizes. Bayesian and maximum likelihood phylogenetic analyses of sequence data indicated that the allopatric Sierra Nevada population is also a distinct lineage with respect to the larger species range in North America; we suggest a subspecies designation for this lineage should be considered (Strix nebulosa yosemitensis). Our study underscores the importance of phylogeographic studies for identifying lineages of conservation concern, as well as the important role of Pleistocene glaciation events in driving genetic differentiation of avian fauna.

Estimation of Species Identification Error: Implications for Raptor Migration Counts and Trend Estimation

Abstract One of the primary assumptions associated with many wildlife and population trend studies is that target species are correctly identified. This assumption may not always be valid, particularly for species similar in appearance to co-occurring species. We examined size overlap and identification error rates among Coopers (Accipiter cooperii) and sharp-shinned (A. striatus) hawks specific to a raptor migration count station along the Pacific Coast of North America. Illustrating the difficulty of distinguishing between these 2 species, we found overlap in 7 metrics among species–sex groups and in 2 metrics between species, and a principal components analysis revealed a continuum of discrete clusters for each species–sex combination in morphospace. Among juvenile hawks (n  =  940), we found the greatest misidentification rate for male Coopers hawks (23% of the 156 males were identified as sharp-shinned), lesser error rates for female Coopers (8%, n  =  339) and female sharp-shinned (6%, n  =  246), and the lowest misidentification rate for male sharp-shinned hawks (0%, n  =  199). We observed a similar pattern of misidentification among adult hawks (n  =  48). We attempted to use conditional probabilities (identification rates) from calibration data to calculate the true number of adult and juvenile Coopers hawks and sharp-shinned hawks. Discrepancies between total number of observed accipiters and estimated number using calibration data suggest that daily observer misclassification rates are higher than misclassification rates estimated from calibration data and prevent correction of the raw data. Our results illustrate the importance of testing for and quantifying observer error in species identification in wildlife census and population trend studies particularly when target species may be easily confused with other nontarget species.

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.

Winter Distribution and Conservation Status of the Sierra Nevada Great Gray Owl

ABSTRACT Little information is available on the winter ecology of the small, geographically isolated, genetically-unique population of great gray owls (Strix nebulosa) in the central Sierra Nevada, California. This population is comprised of facultative, elevational winter migrants and access to winter habitat is an important component of their ecology. Winter observations and remotely sensed habitat variables were used to inform a predictive model of the environmental requirements and geographic distribution of this owl population. Using the modeled distribution map we assessed the distribution of 20% probability of occurrence classes relative to owl habitat associations, ownership, current development, and projected future development patterns. Our findings indicate that high probability class (81–100%) areas and the broader joint medium/medium-high/high probability class (41–100%) areas are uncommon on the landscape (0.2% and 5.0% of study area, respectively). High probability areas were characterized by Sierran Yellow Pine forest surrounding relatively small, flat areas of grassland, wet meadow, and riparian habitats, within the mid-elevation range. Approximately 32% of the high probability areas and 48% of the medium/medium-high/ high probability areas occur on private lands. Of the areas on private lands, 32% of the high probability and 42% of the medium/medium-high/high probability areas occur on currently developed lands. Projected future development on private lands indicated that an additional 12% of the high and 18% of medium/ medium-high/high suitability areas are slated for development by the year 2040. Future conservation planning efforts for the great gray owl in the Sierra Nevada will need to address management issues on both public and private lands. For future planning of development projects around great gray owl wintering habitat, the results from our study supplement current knowledge of breeding distributions to provide land and wildlife managers guidance on conservation priorities.

WEST NILE VIRUS ANTIBODY SURVEILLANCE IN THREE SIERRA NEVADA RAPTORS OF CONSERVATION CONCERN

Abstract. West Nile virus (WNV) infection has caused high levels of mortality in North American hawks and owls. To investigate the extent of infection among raptors of conservation concern in the Sierra Nevada, we tested 62 Northern Goshawks (Accipiter gentilis), 209 Spotted Owls (Strix occidentalis), and 22 Great Gray Owls (Strix nebulosa) for WNV antibodies during the summers of 2004 to 2007 and compared our results with avian WNV mortalities detected by the California Department of Public Health. We detected no antibodies to WNV among the individuals tested. During the same period WNV RNA was detected in dead birds from 26 species in the Sierra Nevada region. These results suggest that the populations we studied were not exposed, that the level of WNV infection was so low as to be undetectable by our sampling scheme, or that the mortality rate from WNV was high enough to leave no surviving individuals; there is no independent evidence of the last alternative.

Development of 37 microsatellite loci for the great gray owl (Strix nebulosa) and other Strix spp. owls

We developed 37 great gray owl (Strix nebulosa) microsatellite primers from CA and TAGA enriched genomic libraries. Primers were tested in 15 great gray owls from California, USA and Alberta, Canada as well as two other Strix species, spotted owl (S. occidentalis) and barred owl (S. varia). These markers will have broad application in investigations of Strix population structure and genetic diversity.

A new subspecies of great gray owl (Strix nebulosa) in the Sierra Nevada of California, U.S.A.

UNA NUEVA SUBESPECIE DE STRIX NEBULOSA EN LA SIERRA NEVADA DE CALIFORNIA, EEUU Brindamos un diagnóstico para una nueva subespecie de Strix nebulosa para el centro de la Sierra Nevada de California basados en previos análisis filogenéticos y genéticos poblacionales y en la distribución alopátrica. La nueva subespecie está definida por análisis filogenéticos de 1920 pares de bases de una región de control y en la subunidad 2 de la NADH deshidrogenasa de una secuencia de ADN mitocondrial y respaldada por una diferenciación genética poblacional en 30 marcadores de ADN microsatelital nuclear. La distribución de esta subespecie incluye ecosistemas boscosos y forestales y praderas asociadas entre los 700 m y 2600 m en el centro de la Sierra Nevada en California, EEUU. Esta subespecie de S. nebulosa está amenazada por numerosos factores y justifica esfuerzos de conservación continuos.