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Inbreeding has been difficult to quantify in wild populations because of incomplete parentage information. We applied and extended a recently developed framework for addressing this problem to infer inbreeding rates in Northern Spotted Owls (Strix occidentalis caurina) across the Pacific Northwest, USA. Using pedigrees from 14,187 Northern Spotted Owls, we inferred inbreeding rates for 14 types of matings among relatives that produce pedigree inbreeding coefficients of F = 0.25 or F = 0.125. Inbreeding was most common in the Washington Cascades, where an estimated 15% of individuals are inbred. Inbreeding was lowest in western Oregon (3.5%) and northern California (2.7%), and intermediate for the Olympic Peninsula of Washington (6.1%). Estimates from the Olympic Peninsula were likely underestimates because of small sample sizes and the presence of few pedigrees capable of resolving inbreeding events. Most inbreeding resulted from matings between full siblings or half siblings, although a high rat...

Trail-based recreation is a popular use of public forests in the United States, and four types are common: all-terrain vehicle (ATV) riding, mountain biking, hiking, and horseback riding. Effects on wildlife, however, are controversial and often a topic of land use debates. Accordingly, we studied trail-based recreation effects on elk (Cervus canadensis), a wide-ranging North American ungulate highly sought for hunting and viewing on public forests, but that is sensitive to human activities, particularly to motorized traffic on forest roads. We hypothesized that elk would respond to trail-based recreation similarly to their avoidance of roads open to motorized traffic on public forests. We evaluated elk responses using a manipulative landscape experiment in a 1453-ha enclosure on public forest in northeast Oregon. A given type of recreation was randomly selected and implemented twice daily along 32 km of designated recreation trails over a five-day period, followed by a nine-day control period of no human activity. Paired treatment and control replicates were repeated three times per year for each recreation type during spring-fall, 2003–2004. During treatments, locations of elk and recreationists were simultaneously collected with telemetry units. Elk locations also were collected during control periods. Elk avoided the trails during recreation treatments, shifting distribution farther out of view and to areas farthest from trails. Elk shifted distribution back toward trails during control periods of no human activity. Elk avoided recreationists in real time, with mean minimum separation distances from humans that varied from 558 to 879 m among the four treatments, 2–4 times farther than elk distances from trails during recreation. Separation distances maintained by elk from recreationists also were 3–5 times farther than mean distances at which elk could be viewed from trails. Distances between elk and recreationists were highest during ATV riding, lowest and similar during hiking and horseback riding, and intermediate during mountain biking. Our results support the hypothesis that elk avoid trail-based recreation similarly to their avoidance of roads open to motorized traffic on public forests. Forest managers can use results to help optimize trade-offs between competing objectives for trail-based recreation and wildlife species like elk that are sensitive to human activities on public forests.

The northern spotted owl (Strix occidentalis caurina) was listed as threatened under the U.S. Endangered Species Act (ESA) in 1990. We applied modern spatial conservation theory and models to evaluate several candidate critical habitat networks, and sought an efficient conservation solution that encompassed the highest value lands for spotted owl recovery rather than maximizing the total area of potential critical habitat. We created a map of relative habitat suitability, which served as input to the spatial conservation prioritization program Zonation. We used the spatially-explicit individual-based population model HexSim to estimate and compare simulated spotted owl population outcomes among a suite of candidate critical habitat networks that varied in size and spatial arrangement under alternative scenarios of future habitat suitability and barred owl (S. varia) effects. We evaluated simulated spotted owl population outcomes, including total population size, and extinction and quasi-extinction likelihoods for 108 combinations of candidate critical habitat networks by habitat change by barred owl scenarios, both range-wide and within 11 distinct portions of the owl’s range. Barred owl encounter rates and the amount and suitability of habitat had substantial effects on simulated spotted owl populations. When barred owl encounter rates were high, changes in the amount and suitability of habitat had minimal impacts on population performance. Under lowered barred owl encounter rates, candidate critical habitat networks that included most existing high suitability habitat supported a high likelihood of long-term population persistence. Barred owls are currently the primary driving force behind poor population performance of NSOs; however, our models demonstrated that a sufficient area of high suitability habitat remains essential for recovery when effects of barred owls can be reduced. The modeling approach we employed is sufficiently flexible to incorporate new information about spotted owls as it becomes available and could likely be applied to conservation planning for other species.

Testing the influence of edges on animal distributions depends on our capacity to quantify ‘edge’, particularly in heterogeneous landscapes. Habitat quality is likely to differ in instances where edges are abrupt and anthropogenic in origin, versus diffuse, disturbance-created edges. We tested whether or not structurally distinct edge types influence northern spotted owl habitat selection and whether the relationship between edge type and use varied across spatial scales relevant to owl foraging (

We used multi-season occupancy analyses to model 2 fates of northern spotted owl territories in relation to habitat amount, habitat fragmentation, and the presence of barred owls in Washington State, USA, 1989–2005. Local colonization is the probability a territory unoccupied by a spotted owl in year i would be occupied in year i + 1, and local extinction is the probability a territory that was occupied by a spotted owl in year i would be unoccupied in year i + 1. We found a negative relationship between local extinction probability and amount of late-seral forest edge. We found a negative relationship between colonization probability and the number of late-seral forest patches (higher fragmentation), and a negative relationship between colonization probability and the amount of non-habitat within 600 m of a spotted owl territory center (Akaike weight = 0.59). The presence of barred owls was positively related to extinction probability and negatively related to detection probability of spotted owls. The negative relationship between presence of barred owls and detectability of spotted owls indicated that spotted owls could be modifying their calling behavior in the presence of barred owls. The positive relationship between barred owl detections and local extinction probability suggests that because of competition with barred owls, spotted owls are being displaced. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Cougars (Puma concolor) are a primary predator of mule deer (Odocoileus hemionus) and elk (Cervus elaphus) throughout western North America. Effective management of predator-prey systems requires a solid understanding of kill rates, prey use, and selection. We implemented a 3-year study in northeast Oregon to investigate cougar diet, kill rates, and prey selection in a multiple-prey system to assess the degree to which patterns in cougar predation may be generalizable across systems and to identify selective predation patterns of cougars that may affect ungulate populations. We marked 25 adult cougars with global positioning system (GPS) collars and monitored predation sequences for 7,642 days to identify kill sites. In field investigation of kill sites, we identified remains of 1,213 prey items killed by cougars, of which 1,158 (95.4%) were native ungulates. On average, cougars killed 1.03 ungulates/week (95% CI = 0.92–1.14), but kill rates varied by season, sex, and reproductive status of cougars. Cougars killed ungulate prey 1.55 (95% CI = 1.47–1.66) times more frequently during summer (May–Oct) than winter (Nov–Apr). Kill rates were higher in summer because juvenile ungulates were the most frequently killed prey item and were smaller than prey killed in winter. Female cougars with kittens >6 months old killed prey more frequently than males, solitary females, and females with kittens 6 months old demonstrated little selection for any age class or species of prey, highlighting an opportunistic foraging strategy to maximize energy gains while feeding young. Across all cougars, we observed a pattern of selection for adult male deer during winter but not summer and did not observe patterns of selection for adult elk according to sex. Our results strongly supported the hypothesis proposed by [Knopff et al. (2010) Journal of Wildlife Management, 74: 1435–1447] that cougar predation is influenced by season and demographic classifications of cougars and our results provide strong evidence that this hypothesis should be generalizable to other areas. The patterns of selection for juvenile elk and deer suggested wildlife managers should consider the potential negative effects of cougars on ungulate populations in areas where juvenile recruitment has been chronically low. © 2014 The Wildlife Society.

Cougar (Puma concolor) management in Oregon is unique because hunting cougars with dogs was allowed through the 1994 hunting season, but thereafter Ballot Initiative Measure 18 prohibited the use of dogs to pursue cougars. Since 1995, hunting seasons have become increasingly longer with more tags sold. The effects of changing management structure on survival rates and causes of mortality of cougars are not well understood. We investigated survival and documented causes of mortality of radiocollared cougars at 3 study areas in Oregon from 1989 to 2011 under contrasting management strategies. The Catherine Creek (1989–1996) and Jackson Creek (1993–2002) studies overlapped the prohibition of hunting cougars with dogs, and the Wenaha, Sled Springs, and Mt. Emily (WSM) study was conducted from 2002 to 2011 when hunting cougars with dogs was illegal. Hunting mortality was the most common cause of death for sub-adult and adult cougars in Catherine Creek pre- (18 of 23 mortalities) and post-Measure 18 (1 of 2 mortalities) and WSM (24 of 53 mortalities) study areas in northeast Oregon. In contrast, natural mortality was the most common cause of death of sub-adults and adults at the Jackson Creek (25 of 38 mortalities) study area in southwest Oregon, but hunting mortality was most common prior to the passage of Measure 18 (3 of 3 mortalities). We estimated annual survival rates of cougars using known fate models in Program MARK. Annual survival rates of adult males were lowest at Catherine Creek prior to the passage of Measure 18 ( = 0.57; 95% CI = 0.39–0.73) and increased after Measure 18 ( = 0.86; 95% CI = 0.79–0.92), which were similar to those rates observed at Jackson Creek pre- and post-Measure 18 ( = 0.78; 95% CI = 0.65–0.88) and WSM ( = 0.82; 95% CI = 0.69–0.91). Regardless of hunting regulations, annual survival rates of adult females was similar among study areas (Catherine Creek pre- and post-Measure 18 [ = 0.86; 95% CI = 0.79–0.92]; Jackson Creek pre- and post-Measure 18 [ = 0.85; 95% CI = 0.77–0.91]; WSM [ = 0.85; 95% CI = 0.76–0.90]). At Jackson Creek pre- and post-Measure 18 and WSM, sub-adult males (1–3 years) had significantly lower survival than sub-adult females, but survival rates of males and females were similar by age 4 or 5 years. At WSM, survival declined for both sexes at older ages (8–13 years), but this decline was not observed at Jackson Creek pre- or post-Measure 18. The effect of increasing age on cougar survival should be considered when using survival rates to estimate population growth rates. We did not detect an effect of age on cougar survival at the Catherine Creek study area pre- or post-Measure 18, which we attributed to selective harvest of prime-aged, male cougars prior to the passage of Measure 18 and lack of mortality post-Measure 18. Managers should understand local sources of mortality when setting harvest regulations because sources of mortality may vary widely within and among jurisdictions, even if management practices are similar. Because of low hunter success rates when hunting cougars without dogs, survival rates of cougars managed under this hunting regime should be substantially higher than areas where use of dogs is legal. This suggests the ability of managers to effectively manipulate survival rates of cougars to meet population management objectives will be dependent on available hunting methods. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

The federally threatened northern spotted owl (Strix occidentalis caurina) is the focus of intensive conservation efforts that have led to much forested land being reserved as habitat for the owl and associated wildlife species throughout the Pacific Northwest of the United States. Recently, however, a relatively new threat to spotted owls has emerged in the form of an invasive competitor: the congeneric barred owl (S. varia). As barred owls have rapidly expanded their populations into the entire range of the northern spotted owl, mounting evidence indicates that they are displacing, hybridizing with, and even killing spotted owls. The range expansion by barred owls into western North America has made an already complex conservation issue even more contentious, and a lack of information on the ecological relationships between the 2 species has hampered recovery efforts for northern spotted owls. We investigated spatial relationships, habitat use, diets, survival, and reproduction of sympatric spotted owls and barred owls in western Oregon, USA, during 2007–2009. Our overall objective was to determine the potential for and possible consequences of competition for space, habitat, and food between these previously allopatric owl species. Our study included 29 spotted owls and 28 barred owls that were radio-marked in 36 neighboring territories and monitored over a 24-month period. Based on repeated surveys of both species, the number of territories occupied by pairs of barred owls in the 745-km2 study area (82) greatly outnumbered those occupied by pairs of spotted owls (15). Estimates of mean size of home ranges and core-use areas of spotted owls (1,843 ha and 305 ha, respectively) were 2–4 times larger than those of barred owls (581 ha and 188 ha, respectively). Individual spotted and barred owls in adjacent territories often had overlapping home ranges, but interspecific space sharing was largely restricted to broader foraging areas in the home range with minimal spatial overlap among core-use areas. We used an information-theoretic approach to rank discrete-choice models representing alternative hypotheses about the influence of forest conditions, topography, and interspecific interactions on species-specific patterns of nighttime resource selection. Spotted owls spent a disproportionate amount of time foraging on steep slopes in ravines dominated by old (>120 yr) conifer trees. Barred owls used available forest types more evenly than spotted owls, and were most strongly associated with patches of large hardwood and conifer trees that occupied relatively flat areas along streams. Spotted and barred owls differed in the relative use of old conifer forest (greater for spotted owls) and slope conditions (steeper slopes for spotted owls), but we found no evidence that the 2 species differed in their use of young, mature, and riparian-hardwood forest types. Mean overlap in proportional use of different forest types between individual spotted owls and barred owls in adjacent territories was 81% (range = 30–99%). The best model of habitat use for spotted owls indicated that the relative probability of a location being used was substantially reduced if the location was within or in close proximity to a core-use area of a barred owl. We used pellet analysis and measures of food-niche overlap to determine the potential for dietary competition between spatially associated pairs of spotted owls and barred owls. We identified 1,223 prey items from 15 territories occupied by spotted owls and 4,299 prey items from 24 territories occupied by barred owls. Diets of both species were dominated by nocturnal mammals, but diets of barred owls included many terrestrial, aquatic, and diurnal prey species that were rare or absent in diets of spotted owls. Northern flying squirrels (Glaucomys sabrinus), woodrats (Neotoma fuscipes, N. cinerea), and lagomorphs (Lepus americanus, Sylvilagus bachmani) were primary prey for both owl species, accounting for 81% and 49% of total dietary biomass for spotted owls and barred owls, respectively. Mean dietary overlap between pairs of spotted and barred owls in adjacent territories was moderate (42%; range = 28–70%). Barred owls displayed demographic superiority over spotted owls; annual survival probability of spotted owls from known-fate analyses (0.81, SE = 0.05) was lower than that of barred owls (0.92, SE = 0.04), and pairs of barred owls produced an average of 4.4 times more young than pairs of spotted owls over a 3-year period. We found a strong, positive relationship between seasonal (6-month) survival probabilities of both species and the proportion of old (>120 yr) conifer forest within individual home ranges, which suggested that availability of old forest was a potential limiting factor in the competitive relationship between these 2 species. The annual number of young produced by spotted owls increased linearly with increasing distance from a territory center of a pair of barred owls, and all spotted owls that attempted to nest within 1.5 km of a nest used by barred owls failed to successfully produce young. We identified strong associations between the presence of barred owls and the behavior and fitness potential of spotted owls, as shown by changes in movements, habitat use, and reproductive output of spotted owls exposed to different levels of spatial overlap with territorial barred owls. When viewed collectively, our results support the hypothesis that interference competition with barred owls for territorial space can constrain the availability of critical resources required for successful recruitment and reproduction of spotted owls. Availability of old forests and associated prey species appeared to be the most strongly limiting factors in the competitive relationship between these species, indicating that further loss of these conditions can lead to increases in competitive pressure. Our findings have broad implications for the conservation of spotted owls, as they suggest that spatial heterogeneity in vital rates may not arise solely because of differences among territories in the quality or abundance of forest habitat, but also because of the spatial distribution of a newly established competitor. Experimental removal of barred owls could be used to test this hypothesis and determine whether localized control of barred owl numbers is an ecologically practical and socio-politically acceptable management tool to consider in conservation strategies for spotted owls. © 2013 The Wildlife Society

We investigated the movements and selection of settlement sites of translocated pygmy rabbits (Brachylagus idahoensis) in southeastern Oregon from June to December 2008. We captured, radio tagged, and translocated 59 pygmy rabbits across big sagebrush (Artemisia tridentata ssp.) habitat with 3 categories of landscape fragmentation. We used radio telemetry to track the movements and document the fates of translocated individuals. We used Geographic Information Systems (GIS) and spatial analysis software (FRAGSTATS) to analyze the post-release movements and selection of settlement sites by pygmy rabbits. We found that pygmy rabbits settled closer to their release sites as the amount big sagebrush cover on the surroundinglandscapeincreased.Inaddition,translocatedpygmyrabbits settled onsitesthat,onaverage,had greater cover, greater landscape connectivity, and fewer but larger patches of big sagebrush than were present at their capture sites. Current or past presence of conspecifics also appeared to be a factor in selection of settlement sites by pygmy rabbits. Successful translocation of wild pygmy rabbits for augmenting depleted populations will require selection of release locations with continuous big sagebrush cover and a history of pygmy rabbit presence. Managers should also expect to lose a portion of translocated pygmy rabbits to homing attempts, post-release dispersal, and predation, so large numbers of individuals should be released to establish resident populations. 2013 The Wildlife Society.

This is the publisher’s final pdf. The article is copyrighted by The Wildlife Society and published by John Wiley & Sons, Inc. It can be found at: http://onlinelibrary.wiley.com/doi/10.1002/jwmg.v77.4/issuetoc. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.

In the Klamath province of southwestern Oregon, Northern Spotted Owls (Strix occidentalis caurina) occur in complex, productive forests that historically supported frequent fires of variable severity. However, little is known about the relationships between Spotted Owl survival and home-range size and the characteristics of fire-prone, mixed-conifer forests of the Klamath province. Thus, the objectives of this study were to estimate monthly survival rates and home-range size in relation to habitat characteristics for Northern Spotted Owls in southwestern Oregon. Home-range size and survival of 15 Northern Spotted Owls was monitored using radiotelemetry in the Ashland Ranger District of the Rogue River–Siskiyou National Forest from September 2006 to October 2008. Habitat classes within Spotted Owl home ranges were characterized using a remote-sensed vegetation map of the study area. Estimates of monthly survival ranged from 0.89 to 1.0 and were positively correlated with the number of late-seral h...

Habitat fragmentation is hypothesized to influence movements of animals between isolated habitat fragments and to affect survival of animals moving between fragments. Translocation experiments can provide quantitative information on movements and survival. We assessed potential barriers to dispersal and survival of pygmy rabbits (Brachylagus idahoensis), a species of conservation concern that is hypothesized to be sensitive, after translocation, to fragmentation of its sagebrush habitats. We measured homing tendency and estimated survival of pygmy rabbits after short-distance (1–2 km) experimental translocations at sites in southeastern Oregon. We captured, radio-tagged, and translocated 59 pygmy rabbits across 3 landscape categories of habitat fragmentation. We used logistic regression to compare among landscapes the odds of homing, after accounting for sex and displacement distance of individuals. We used known-fate models in program MARK to estimate survival rates of rabbits after translocation. Fifteen percent of translocated pygmy rabbits successfully homed to within 150 m of their original capture locations. Individuals translocated across fragmented landscapes with patchy cover of big sagebrush were the most likely to home, whereas rabbits translocated across relatively continuous big sagebrush cover bisected by a road were least likely to home. We also found that pygmy rabbits that homed had higher survival rates than those that did not return to their hoirie areas, and rabbits that settled near roads had lower survival rates than those that did not settle near roads. The proximity of the largest patch of big sagebrush also had a positive influence on the survival of rabbits after translocation. Our results indicate that fragmentation does not necessarily impede movements nor does it necessarily reduce survival.

The distribution and geographic range of Greater Sage-Grouse (Centrocercus urophasianus) have been reduced by 56% since European settlement. Although loss and fragmentation of sagebrush (Artemisia spp.) habitats have been cited as the primary causes for the decline of the species, degradation of existing habitat also has been considered an important factor. Guidelines for protection and management of breeding and winter habitat have been developed for land managers, but winter habitat use has not been thoroughly described throughout the species' range, particularly for the western portion of its range in Oregon. We examined vegetation-type selection and use by Greater Sage-Grouse during winter (Nov-Feb) at 3 study areas in southeastern Oregon (1989-1992). Elevation gradients and vegetative communities differed among these 3 areas. Our objective was to examine the geographic variation in the selection and use of various vegetation types during winter, when sage-grouse distributions may be most restricted. We described differences in vegeta- tion structure at the microhabitat scale among 3 areas and differences in vegetation-type selection at the macrohabitat scale. We found that the use of mixed sagebrush (basin big sagebrush (Artemisia tridentata tridentata)) and other shrubby vegetation types by sage-grouse was greater than expected at all 3 study areas. At the low- and high-elevation study areas, low sagebrush (Artemisia longiloba) vegetation types were selected more often than expected at random, which was contrary to our original hypotheses. Basin big sagebrush vegetation types were used in proportion to their availability at the 2 low-elevation study areas, and big sagebrush steppe was used less than available (avoided) at the low-elevation areas; these results were contrary to our original predictions. Such differences in selection among the study areas in southeastern Oregon create additional challenges for land managers, who are charged with managing habitats for sage-grouse use during autumn and winter in this portion of the species' geographic range.

We investigated the effects of predation risk on birth-site selection by Rocky Mountain elk (Cervus elaphus nelsoni) during summer in 2002–2004 in northeastern Oregon at macrohabitat (3rd-order selection) and microhabitat (4th-order selection) scales. This study describes vegetative characteristics of birth sites selected by female elk when young ,4–5 days old used the hiding strategy and predation sites when most predation events occurred on young .5 days old that used the fleeing strategy. At the macrohabitat scale we observed no evidence that female elk were influenced by predation risk when selecting a birth site on the basis of variables measured in this study. Females chose birth sites with less overhead cover than random sites, suggesting that they might have been influenced more by forage availability than predation risk. At the microhabitat scale females selected birth sites that had more overhead canopy cover and greater visibility at ground level than paired random sites, which suggested that birth-site selection at this scale was influenced by predation risk. Together, these results suggested that female elk selected areas for parturition at the macrohabitat scale that likely had forage to meet high nutritional demands of lactation and at the microhabitat scale selected areas that provided visibility to detect predators and reduce the risk of predation. Predators, mainly cougars (Puma concolor), killed young in areas closer to vegetative edges at the macrohabitat scale and with more visibility at the microhabitat scale. These areas were likely conducive to cougar hunting where sight and cover from forest edges can be important for stalking calves that are traveling with their mothers and family groups.

We examined associations between annual reproduction and climate for 6 populations of individually marked northern spotted owls (Strix occidentalis caurina) in Washington and Oregon. We used an information-theoretical approach and mixed models to evaluate statistical models representing a priori hypotheses about the effects of weather and climate on reproduction. Reproduction was higher for adult than subadult owls and declined as the proportion of spotted owl territories with barred owl (Strix varia) detections increased. Similar to other spotted owl studies, we found that reproduction was negatively associated with cold, wet winters and nesting seasons at 3 of 6 study areas. In addition, we identified new relationships between reproduction, annual precipitation, storms, and regional climate cycles. For 3 of 6 areas, we found a quadratic relation between precipitation (rain and snow) and reproduction, with the number of young fledged per pair per year declining as precipitation in the previous year deviated from average levels. A meta-analysis conducted across all 6 areas indicated that reproduction at the regional level had a quadratic association with total winter snowfall in the preceding winter and was positively related to temperatures during the previous summer and fall. The amount of annual variation in reproduction accounted for by weather and climate varied widely across the 6 areas (4-79%), whereas variation in weather and climate across owl territories accounted for little of the spatial variation in reproduction (0-4%). Our results suggest that across the range of the species climate factors affecting prey abundance may have a greater effect on reproduction than direct effects of weather on nestlings. 2011 The Wildlife Society.

We studied resource partitioning between sympatric populations of Columbian white-tailed (CWTD; Odocoileus virginianus leucurus) and black-tailed (BWTD) deer (O. odocoileus hemionus columbianus) in western Oregon to understand potential mechanisms of coexistence. We used horseback transects to describe spatial distributions, population overlap, and habitat use for both species, and we studied diets with microhistological analysis of fecal samples. Distribution patterns indicated that white-tailed and black-tailed deer maintained spatial separation during most seasons with spatial overlap ranging from 5%–40% seasonally. Coefficients of species association were negative, suggesting a pattern of mutual avoidance. White-tailed deer were more concentrated in the southern portions of the study area, which was characterized by lower elevations, more gradual slopes, and close proximity to streams. Black-tailed deer were more wide ranging and tended to occur in the northern portions of the study area, whi...

The range expansion by barred owls (Strix varia) into western North America has raised considerable concern regarding their potential effects on declining northern spotted owl (Strix occidentalis caurina) populations, yet most information on the occurrence of barred owls in the region is limited to incidental detections during surveys for spotted owls. To address this shortcoming we investigated response behavior, detection probabilities, and landscape occupancy patterns of barred owls in western Oregon, USA, during conspecific versus spotted owl call-broadcast surveys. Subtle differences in barred owl response behavior to conspecific versus spotted owl vocalizations combined with minor procedural differences between species-specific survey protocols led to a sizeable difference in estimated detection probabilities during conspecific (0.66, 95% CI ¼ 0.61-0.71) versus spotted owl (0.48, 95% CI ¼ 0.39-0.56) surveys. We identified 61 territorial pairs of barred owls during repeated surveys of a multi-ownership study area with the probability of occupancy being highest in the structurally diverse mixture of mature and old forests that occurred almost entirely on public lands. Our findings suggest that research and management strategies to address potential competitive interactions between spotted owls and barred owls will require carefully designed, species-specific survey methods that account for erratic response behaviors and imperfect detection of both species. Our sampling methods can be used by forest managers to determine the occurrence and distribution of barred owls with high confidence. 2011 The Wildlife Society.

We estimated annual survival rates (S) of 23 radio-marked Northern Spotted Owls (Strix occidentalis caurina) at the Quartz and Timbered Rock burns and adjacent areas in southwest Oregon. We used known-fate models in program MARK to test for differences in survival among three groups (owls dwelling inside of burned areas, owls displaced by wildfire, and owls dwelling outside of burned areas) and to investigate the potential effects of fire severity and cover type on survival. We found that annual survival rates of Spotted Owls that maintained a territory within the burn perimeter (Ŝ = 0.69 ± 0.12) or that had been displaced by the burn (Ŝ = 0.66 ± 0.14) were lower than those of owls that had territories outside but adjacent to the burn perimeter (Ŝ = 0.85 ± 0.06). This result indicated that wildfire had a negative impact on Spotted Owl survival, at least in the short-term (i.e., 3–5 yr postburn). We were unable to identify a significant effect of fire severity or quantity of habitat on Spotted Owl...

We used an information-theoretical approach and Cormack—Jolly—Seber models for open populations in program MARK to examine relationships between survival rates of Northern Spotted Owls and a variety of local weather variables and long-term climate variables. In four of the six populations examined, survival was positively associated with wetter than normal conditions during the growing season or high summer temperatures. At the three study areas located at the highest elevations, survival was positively associated with winter temperature but also had a negative or quadratic relation with the number of storms and winter precipitation. A meta-analysis of all six areas combined indicated that annual survival was most strongly associated with phase shifts in the Southern Oscillation and Pacific Decadal Oscillation, which reflect large-scale temperature and precipitation patterns in this region. Climate accounted for a variable amount (1–41%) of the total process variation in annual survival but for ...

We used reverse time capture-mark-recapture models to describe associations between rate of population change (k) and climate for northern spotted owls (Strix occidentalis caurina) at six long-term study areas in Washington and Oregon, USA. Populations in three of six areas showed strong evidence of declining populations, while populations in two additional areas were likely declining as well. At four areas, k was positively associated with wetter-than-normal conditions during the growing season, which likely affects prey availability. Lambda was also negatively associated with cold, wet winters and nesting seasons, and the number of hot summer days. The amount of annual variation in k accounted for by climate varied across study areas (3–85%). Rate of population change was more sensitive to adult survival than to recruitment; however, there was considerable variation among years and across study areas for all demographic rates. While annual survival was more closely related to regional climate conditions, recruitment was often associated with local weather. In addition to climate, declines in recruitment at four of six areas were associated with increased presence of barred owls. Climate change models predict warmer, wetter winters and hotter, drier summers for the Pacific Northwest in the first half of the 21st century. Our results indicate that these conditions have the potential to negatively affect annual survival, recruitment, and consequently population growth rates for northern spotted owls.

Factors influencing the survival of pygmy rabbits (Brachylagus idahoensis) are poorly understood and have received minimal attention in previous studies. We investigated survival and causes of mortality of pygmy rabbits in southeastern Oregon and northwestern Nevada. We trapped 298 rabbits on 4 sites and fitted each with radiotransmitters. We used known-fate models in program MARK to estimate survival rates of radiomarked pygmy rabbits from September 2005 to August 2006. The best model, based on Akaike's information criterion, indicated that survival rates varied among study sites, sexes, and with monthly interval in a parallel pattern [model S (area * sex + t)]. The estimated annual survival rate on the 4 study sites was notably low and varied from 0.003 (SE = 0.003) to 0.173 (SE = 0.066). Predation on radiomarked rabbits was high for both adult (88.6%) and juvenile (89.4%) rabbits. When the predator species could be determined, the most common predators of pygmy rabbits were coyotes (Canis ...

Although estimations of vital rates are important to understand population dynamics of small mammals, there is little information on survival rates and causes of mortality for many species. In 2002–2003, we estimated monthly and annual survival of 50 radiocollared red tree voles (Arborimus longicaudus) during a study of movements and diel activity patterns in western Oregon. Estimated annual survival for both sexes combined was 0.15 (95% CI = 0.06 to 0.31) and was influenced little by mass at initial capture. In the analysis of explanatory variables, we did not find strong effects of gender, vole age, or forest age on survival. We suspect this may have been due to small sample size and low power to detect effects, because some of the point estimates were suggestive of large differences among groups. Most mortality was due to predation, with 15 of 25 deaths attributed to weasels (Mustela spp.). Weasels preyed upon significantly more females than males (14:1, respectively). Other confirmed or suspe...

The Washington ground squirrel (Urocitellus washingtoni) is listed as threatened in Oregon and is a species of special concern in Washington. We investigated abundance and habitat selection of the species on the Boardman Bombing Range, Morrow County, Oregon during 1996–1997. Transect surveys were used to determine relative abundance among seven vegetative types, and mark-recapture methods were used to compare density of squirrels among habitats where they were present. Transect surveys indicated highest abundance in sagebrush, followed by perennial grassland then annual grassland; and no squirrels were detected in bitterbrush or low-shrub habitats. Results from live-trapping and capture-recapture methods also indicated higher densities in sagebrush habitat. Mean maximum distance moved on trapping grids was greater for males than females for adults and juveniles alike. Macro-habitat analyses revealed a selection for areas with higher silt content (Warden soils) in soils and higher vegetative cover...

We estimated survival rates of 135 female greater sage-grouse (Centrocercus urophasianus) on 3 study areas in southeastern Oregon, USA during autumn and winter for 3 years. We used known-fate models in Program MARK to test for differences among study areas and years, investigate the potential influence of weather, and compute estimates of overwinter survival. We found no evidence for differences in survival rates among study areas, which was contrary to our original hypothesis. There also were no declines in survival rates during fall–winter, but survival rates varied among years and time within years. Average survival rate from October through February was 0.456 (SE = 0.062). The coefficient of variation for this estimate was 13.6% indicating good precision in our estimates of survival. We found strong evidence for an effect of weather (i.e., mean daily min. temp, extreme min. temp, snow depth) on bi-weekly survival rates of sage-grouse for 2 of the study areas in one year. Extremely low (

Off-road recreation on public lands in North America has increased dramatically in recent years. Wild ungulates are sensitive to human activities, but the effect of off-road recreation, both motorized and nonmotorized, is poorly understood. We measured responses of elk (Cervus elaphus) to recreational disturbance in northeast Oregon, USA, from April to October, 2003 and 2004. We subjected elk to 4 types of recreational disturbance: all-terrain vehicle (ATV) riding, mountain biking, hiking, and horseback riding. Motion sensors inside radiocollars worn by 13 female elk recorded resting, feeding, and travel activities at 5-minute intervals throughout disturbance and control periods. Elk fed and rested during control periods, with little time spent traveling. Travel time increased in response to all 4 disturbances and was highest in mornings. Elk travel time was highest during ATV exposure, followed by exposure to mountain biking, hiking, and horseback riding. Feeding time decreased during ATV exposure and resting decreased when we subjected elk to mountain biking and hiking disturbance in 2003. Our results demonstrated that activities of elk can be substantially affected by off-road recreation. Mitigating these effects may be appropriate where elk are a management priority. Balancing management of species like elk with off-road recreation will become increasingly important as off-road recreational uses continue to increase on public lands in North America.

Livestock grazing is common and widespread throughout North America, yet few studies have evaluated its effects on small mammals. We studied small mammals in mixed-conifer forests and oak woodlands on the Cascade–Siskiyou National Monument in southern Oregon, USA, to 1) evaluate small-mammal microhabitat associations, 2) identify riparian-associated species, and 3) test the hypothesis that grazing does not influence small mammals after accounting for microhabitat associations. We live-trapped small mammals at 16 study sites and used logistic regression to model probability of capture on measured habitat characteristics at each trap station and to evaluate effects of grazing. Over 2 years, we trapped 1,270 individual small mammals representing 18 species. Odds of capturing western harvest mice (Reithrodontomys megalotis), dusky-footed woodrats (Neotoma fuscipes), and long-tailed voles (Microtus longicaudus) were lower (P < 0.05) on heavily versus lightly grazed sites. Odds of capture for deer mice...

Because sea otters (Enhydra lutris) exert a wide array of direct and indirect effects on coastal marine ecosystems throughout their geographic range, we investigated the potential influence of sea otters on the ecology of Bald Eagles (Haliaeetus leucocephalus) in the Aleutian Islands, Alaska, USA. We studied the diets, productivity, and density of breeding Bald Eagles on four islands during 1993-1994 and 2000-2002, when sea otters were abundant and scarce, respectively. Bald Eagles depend on nearshore marine communities for most of their prey in this ecosystem, so we predicted that the recent decline in otter populations would have an indirect negative effect on diets and demography of Bald Eagles. Contrary to our predictions, we found no effects on density of breeding pairs on four islands from 1993-1994 to 2000-2002. In contrast, diets and diet diversity of Bald Eagles changed considerably between the two time periods, likely reflecting a change in prey availability resulting from the increase and subsequent decline in sea otter populations. The frequency of sea otter pups, rock greenling (Hexagammus lagocephalus), and smooth lumpsuckers (Aptocyclus ventricosus )i n the eagle's diet declined with corresponding increases in Rock Ptarmigan (Lagopus mutus), Glaucous-winged Gulls (Larus glaucescens), Atka mackerel (Pleurogrammus monopterygius), and various species of seabirds during the period of the recent otter population decline. Breeding success and productivity of Bald Eagles also increased during this time period, which may be due to the higher nutritional quality of avian prey consumed in later years. Our results provide further evidence of the wide-ranging indirect effects of sea otter predation on nearshore marine communities and another apex predator, the Bald Eagle. Although the indirect effects of sea otters are widely known, this example is unique because the food-web pathway transcended five species and several trophic levels in linking one apex predator to another.

We compared winter (December, January, and February) and early spring (March and April) bird communities among 4 successional stages that included grassland, shrubsteppe, juniper-shrubsteppe, and old-growth juniper woodland in central Oregon. Birds were surveyed monthly from December through April in 1998/1999 and 1999/2000 using the point count method to estimate relative abundance of birds (individuals · transect−1year−1). We used distance sampling to correct for potential bias in estimating abundance and density among successional stages. A total of 4513 birds (32 species) were detected. Relative abundance of total birds (all species combined) was similar in the juniper-shrubsteppe and old-growth woodland (48.7 and 48.9 individuals · transect−1, respectively) but 6 times greater than in the grassland and shrubsteppe (8.0 and 7.7 individuals · transect−1, respectively) during the 5-month period. Total density of birds was greater in old-growth juniper woodland and juniper-shrubsteppe than in gr...

We developed a snare for collection of black bear (Ursus americanus) hair that obtained a unique hair sample at each snare site, improved the quantity of collected hair compared to barbed-wire corrals, and was easy to deploy over a wide range of topographical features and habitat conditions. This device allowed us to implement intensive sampling methodology needed in mark–recapture experiments with minimal effort. By improving the quantity of hair collected, we also lowered the potential for bear identification errors at the lab. During 2003–2004, bears in 2 study areas triggered snares 1,104 times, which resulted in the collection of 981 hair samples. Of the samples we collected, 79% (775) produced valid genetic data. In 2003, 454 samples identified 79 genetically distinct individuals, and 321 samples identified 86 genetically distinct individuals in 2004. Analysis of capture–recapture data indicated that capture probabilities were affected by heterogeneity among individuals and behavioral respo...

We compared vegetative structure and bird communities among 4 successional states in central Oregon representing a continuum from 1) postburn grassland, 2) mountain big sagebrush–Idaho fescue (Artemisia tridentata–Festuca idahoensis) shrub–steppe, 3) sagebrush–steppe–juniper (Juniperus occidentalis), to 4) old-growth western juniper. Species richness, evenness, and diversity of bird communities were highest in old-growth and mid-successional juniper (22.9 species/transect and 23.6 species/transect, respectively) but lowest in the grasslands (17.6 species/transect). Bird species diversity was positively correlated with physiognomic cover diversity (r = 0.74, P = 0.001). Density of breeding birds was greatest in old-growth juniper (6.6 birds/ha) and lowest in postburn grasslands (3.6 birds/ha) but similar in shrub–steppe and sagebrush–steppe–juniper (6.0 birds/ha and 5.5 birds/ha, respectively). Old-growth juniper had the highest total densities of both tree and cavity nesters. Mountain chickadees ...

The conservation of Spotted Owl (Strix occidentalis) populations has been one of the most controversial and visible issues in United States conservation history. Coincident with declines in Spotted Owl populations over the last three decades has been the invasion of Barred Owls (Strix varia) throughout the range of the Northern Spotted Owl (S. o. caurina) and into the range of the California Spotted Owl (S. o. occidentalis). This invasion has confused the reasons behind recent Spotted Owl declines because anecdotal and correlative information strongly suggests that Barred Owls are a new factor influencing the declines. There is great uncertainty about all aspects of the invasion, and this has sparked discussion about appropriate management and research responses regarding the effects of this invasion on Spotted Owls. We present a set of possible responses to address the issue, and we discuss the relative merits of these with regard to their efficacy given the current state of knowledge. We recommend that research specifically aimed at learning more about the interspecific relationships of these two owls throughout the range of sympatry should begin immediately. Approaches that seem unlikely to be useful in the short-term either because they do not facilitate knowledge acquisition, are relatively costly, or would be technically less feasible, should not be considered viable at this time. We believe the consequences of the invasion are potentially dire for the Spotted Owl and that research and management actions, including the use of adaptive management, are required to inform the near- and long-term decision-making process for conservation of Spotted Owls.

We tested whether extracting lipids reduced confounding variation in δ13C and δ15N values by analyzing paired lipid-extracted (LE) and non-lipid-extracted (NLE) samples of bald eagle ( Haliaeetus leucocephalus (L., 1766)) whole eggs, muscle tissue from nine seabird and one terrestrial bird species, muscle tissue from four marine fish species, and blue mussels ( Mytilus edulis L., 1758) collected from the Aleutian archipelago, Alaska. Lipid extraction significantly increased δ13C by an average of 2.0‰ in whole eggs, 0.8‰ in avian muscle, 0.2‰ in fish muscle, and 0.6‰ in blue mussels. Lower δ13C values in NLE samples covaried positively with lipid content across all sample types. Lower δ13C values in NLE samples were not correlated with lipid content within bald eagle eggs and blue mussels, but covaried positively with percent lipid in avian and fish muscles. Neither lipid extraction nor percent lipid significantly changed δ15N values for any sample type. Lower δ13C values in most NLE avian and fish muscle tissues should not confound interpretation of pelagic versus nearshore sources of primary production, but lipid extraction may be necessary when highly precise estimates of δ13C are needed. Lipid extraction may not be necessary when only δ15N is of interest.

Loehle et al. recently estimated survival rates from radio-telemetered northern spotted owls ( Strix occidentalis caurina (Merriam, 1898)) and suggested that survival rates estimated for this species from capture–recapture studies were negatively biased, which subsequently resulted in the negatively biased estimates of rates of population change (λ) reported by Anthony et al. (Wildl. Monogr. No. 163, pp. 1–47 (2006)) . We argue that their survival estimates were inappropriate for comparison with capture–recapture estimates because (i) the manner in which they censored radio-telemetered individuals had the potential to positively bias their survival estimates, (ii) their estimates of survival were not valid for evaluating bias, and (iii) the size and distribution of their radiotelemetry study areas were sufficiently different from capture–recapture study areas to preclude comparisons. In addition, their inferences of negative bias in rates of population change estimated by Anthony et al. were incorrect and reflected a misunderstanding about those estimators.

Availability of high-quality nest sites is thought to limit breeding populations of American Dippers (Cinclus mexicanus). To examine this hypothesis, we characterized dipper nest sites, nest-site habitat, and productivity in the central Oregon Coast Range. We also made additional nest sites (“created” nest sites = nest boxes, cliff ledges, hollowed logs that we constructed or created) along one of two creeks. Suitable nest sites (1) provided a physical space to place the nest, (2) were above the upper reach of flooding and inaccessible to ground predators, and (3) were very near to, or extended over, the stream's edge. Given these requirements, and within the context of swift, unpolluted mountain streams, dippers exhibited flexibility in their nest-site selection patterns and used a variety of nesting substrates. Streamside features associated with dipper nest sites included geomorphically constrained valleys (i.e., narrow valley floors), the presence of trees in the riparian zone (not tested sta...

We used program CAPTURE to analyze 1,535 capture–recapture data sets from 33 species of small mammals for sources of variation in capture probabilities and to characterize species-specific responses to mark–recapture trapping. Program CAPTURE contains 8 models to account for all possible combinations of heterogeneity (h), behavioral response (b), and time (t) effects on capture probabilities. Model Mo (equal capture probabilities) was selected most often by CAPTURE as the most appropriate model for small sample sizes, reflecting the difficulty of detecting unequal probabilities of capture in small data sets. Heterogeneity in capture probabilities among individuals was evident in larger data sets for all species of small mammals examined. Strong behavioral responses were detected in several species. Sylvilagus, Tamias amoenus, Glaucomys sabrinus, Perognathus longimembris, and Microtus ochrogaster were trap shy, whereas Tamias striatus, Tamias townsendii, Spermophilus richardsonii, Perognathus parvus, Reithrodontomys megalotis, Peromyscus maniculatus, Peromyscus truei, Sigmodon hispidus, Microtus californicus, and Microtus pennsylvanicus were trap prone. Time effects were not apparent for most species except where they were accompanied with heterogeneity. Murid species had the highest estimated probabilities of capture, followed by heteromyids, sciurids, and leporids in decreasing order. Estimates of abundance from model Mh were significantly greater than those from models Mb, Mo, and Mt, which likely reflects the negative bias of these latter estimators.

We used data from Northern Spotted Owl (Strix occidentalis caurina) territories to model the effects of habitat (particularly intermediate-aged forest stand types), climate, and nonhabitat covariates (i.e., age, sex) on owl reproductive rate and apparent survival in southwestern Oregon. Our best model for reproductive rate included an interaction between a cyclic, annual time trend and male breeding experience, with higher reproductive rates in even years compared to odd, particularly for males with previous breeding experience. Reproductive rate was also negatively related to the amount of winter precipitation and positively related to the proportion of old-growth forest near the owl territory center. Apparent survival was not associated with age, sex, climate or any of the intermediate-aged forest types, but was positively associated with the proportion of older forest near the territory center in a pseudothreshold pattern. The quadratic structure of the proportion of nonhabitat farther from the nest or primary roost site was also part of our best survival model. Survival decreased dramatically when the amount of nonhabitat exceeded ∼50%. Habitat fitness potential estimates (λ̂h) for 97 owl territories ranged from 0.29–1.09, with a mean of 0.86 ± 0.02. Owl territories with habitat fitness potentials

We investigated the effects of thinning young (35- to 45-yr-old) Douglas-fir (Pseudotsuga menziesii) forests on density, survival, body mass, movements, and diets of northern flying squirrels (Glaucomys sabrinus) in the northern coast range of Oregon. We used a repeated measures, randomized block design with 3 treatments (control, moderate thinning, and heavy thinning) and 4 replicates to study diets and population characteristics from 1994–1997. Densities of flying squirrels were variable in space and time, but they were positively correlated to biomass and frequency of fungal sporocarps, suggesting they were responding to food resources rather than forest structure. Fungal sporocarps comprised a major portion of the squirrel's diet, and other vegetative material made up the remainder of the diet. Several fungal genera including Gautieria, Geopora, Hymenogaster, Hysterangium, Melanogaster, and Rhizopogon were found more frequently in diets than on the trapping grids and therefore appeared to be ...

Northern spotted owls (Strix occidentalis caurina) have been studied intensively since their listing as a threatened species by the U.S. Fish and Wildlife Service in 1990. Studies of spotted owl site occupancy have used various binary response measures, but most of these studies have made the assumption that detectability is perfect, or at least high and not variable. Further, previous studies did not consider temporal variation in site occupancy. We used relatively new methods for open population modeling of site occupancy that incorporated imperfect and variable detectability of spotted owls and allowed modeling of temporal variation in site occupancy, extinction, and colonization probabilities. We also examined the effects of barred owl (S. varia) presence on these parameters. We used spotted owl survey data from 1990 to 2002 for 3 study areas in Oregon, USA, and we used program MARK to develop and analyze site occupancy models. We found per visit detection probabilities averaged

Northern spotted owls (Strix occidentalis caurina) are known to be associated with late-successional forests in the Pacific Northwest of the United States, but the effects of habitat on their demographic performance are relatively unknown. We developed statistical models relating owl survival and productivity to forest cover types within the Roseburg Study Area in the Oregon Coast Range of Oregon, USA. We further combined these demographic parameters using a Leslie-type matrix to obtain an estimate of habitat fitness potential for each owl territory (n = 94). We used mark–recapture methods to develop models for survival and linear mixed models for productivity. We measured forest composition and landscape patterns at 3 landscape scales centered on nest and activity sites within owl territories using an aerial photo-based map and a Geographic Information System (GIS). We also considered additional covariates such as age, sex, and presence of barred owls (Strix varia), and seasonal climate variable...

We studied a population of Burrowing Owls whose eggs contained the or- ganochlorine compound p,p9DDE and traces of other organochlorine contaminants to de- termine if the levels of contamination were associated with survival or reproduction when nonanthropogenic environmental and biological variables were also considered. Demo- graphic data were collected in conjunction with sampling eggs for contaminants and an- alyzing pellets for dietary information. Levels of p,p9DDE in eggs varied over four orders of magnitude during the study but were not by themselves associated with reproductive failure. However, contaminant concentrations in combination with low rodent abundance in the diet were related to reduced productivity. The variation within and among years in egg contaminants suggests that patterns of egg contaminants are the result of immigrating owls from more contaminated sites, and to a lesser extent, to annual patterns in prey availability. Even low levels of chronic pesticide exposure may be detrimental when com- bined with other stressors, and documentation of the existence of a persistent pesticide in a biotic system is not enough to either infer the origin of the contamination or its potential

Barred Owls (Strix varia) have expanded their range into the Pacific Northwest, and anecdotal evidence suggests that they may be displacing the federally threatened Northern Spotted Owl (Strix occidentalis caurina). Our objectives were to describe the current status of Barred Owls in Oregon and compare occupancy of Spotted Owls in historic Spotted Owl territories before and after Barred Owls were first detected in those territories. Between 1974 and 1998, we estimated that 706 different Barred Owl territories were located in Oregon. From 1989–1998 an average of 60 new Barred Owl territories were located in Oregon each year. In Spotted Owl demographic study areas in Oregon and Washington, Barred Owl detections increased at Spotted Owl territories from 1987–1999. Occupancy of Spotted Owl territories declined after Barred Owls were detected within 0.80 km of the territory center. When Barred Owls were detected 0.81–2.40 km from Spotted Owl territory centers, occupancy of Spotted Owls was only marginally less than at territories without Barred Owls. This suggests that the frequency and intensity of interactions between the two species is negatively associated with distance between them. Our results suggest that land managers and regulatory agencies should regard Barred Owls as a threat to Spotted Owls, particularly if Barred Owls continue to increase in number as they have during the past 25 years. ¿Está Strix varia Desplazando a Strix occidentalis caurina? Resumen. Desde su expansión hacia el Pacífico Noroeste, existe evidencia anecdótica de que Strix varia podría estar desplazando a S. occidentalis caurina. Nuestros objetivos fueron describir el estatus actual de S. varia en Oregon y comparar la ocurrencia de S. occidentalis caurina en sus territorios históricos antes y después de que S. varia se detectó por primera vez en dichos territorios. Entre 1974 y 1998, estimamos que se confirmaron 706 territorios diferentes de S. varia en Oregon. Entre 1989 y 1998, se localizaron en promedio 60 nuevos territorios de S. varia anualmente. En áreas con estudios demográficos de S. occidentalis caurina en Oregon y Washington, las detecciones de S. varia en territorios de S. occidentalis caurina se incrementaron entre 1987 y 1999. En comparación con territorios sin S. varia, la ocupación de territorios de S. occidentalis caurina disminuyó luego de que se detectaron individuos de S. varia a menos de 0.80 km del centro del territorio. Cuando se detectaron individuos de S. varia entre 0.81 y 2.40 km del centro de los territorios, la ocupación de éstos fue sólo marginalmente menor que en territorios sin S. varia. Esto sugiere que la frecuencia e intensidad de la interacción entre las dos especies está asociada con la distancia entre ellas. Nuestros resultados sugieren que las autoridades ambientales y de regulación deben considerar a S. varia como una amenaza para S. occidentalis caurina, particularmente si los números de S. varia se siguen incrementando como en los últimos 25 años.

To describe the composition and pattern of unmanaged forestland in Oregon's central Coast Range, we analyzed forest conditions from a random sample of 18 prelogging (1949 and earlier) landscapes. We also compared the amount and variability of old forest (conifer-dominated stands >53 cm dbh) in the prelogging landscapes with that in the current landscapes. Sixty-three percent of the prelogging landscape comprised old forest, approximately 21% of which also had a significant (>20% cover) hardwood component. The proportions of forest types across the 18 prelogging landscapes varied greatly for both early seral stages (cv=81–194) and hardwoods (cv=127) and moderately for old forest (cv =39). With increasing distance from streams, the amount of hardwoods and nonforest decreased, whereas the amount of seedling/sapling/pole and young conifers increased. The amount of old forest was significantly greater (p< 0.002) in prelogging forests than in current landscapes. Old-forest patterns also differed significantly (p< 0.015) between prelogging and current landscapes; patch density, coefficient of variation of patch size, edge density, and fragmentation were greater in current landscapes and mean patch size, largest patch size, and core habitat were greater in prelogging forests. Generally, old-forest landscape pattern variables showed a greater range in prelogging landscapes than in current landscapes. Management strategies designed to increase the amount of old forest and the range in landscape patterns would result in a landscape more closely resembling that found prior to intensive logging.

To assess the consequences of increased recreational activity in wilderness areas, we studied the effects of human activity on breeding behavior of Bald Eagles (Haliaeetus leucocephalus) in interior Alaska. Activity budgets of breeding eagles changed considerably when humans were camped for 24 h at a distance of 100 m from nests (treatment) compared to when they were camped 500 m from nests (control) (P = 0.0036). With humans near nests, adult eagles decreased the time they preened (percentage change from control to treatment = −53%), slept (−56%), maintained nests (−50%), and fed themselves and their nestlings (−30%) and increased the time they brooded nestlings (+14%). Further, overall activity (total number of behaviors performed by adults at nests per day) decreased by 27% with humans near nests, as did the amount of prey adults consumed (−26%) and fed to nestlings (−29%). In contrast, nest attendance did not change with humans near nests (percentage change = 0.3%, P = 0.9); however, the time adults w...

We studied productivity, diets, and environmental contaminants in nesting bald eagles from the western Aleutian Islands, Alaska, USA, during the summers of 1993 and 1994. Productivity on Adak, Tanaga, and Amchitka Islands ranged from 0.88 to 1.24 young produced per occupied site and was comparable to that of healthy populations in the lower 48 United States. However, productivity on Kiska Island was depressed, averaging 0.67 young per occupied site. The lower reproductive success on Kiska was associated with elevated levels of dichlorodiphenyldichloroethylene and other organochlorine pesticides. Many of the organochlorine pesticides were elevated in bald eagle eggs from the four islands, but concentrations of these contaminants and Hg were significantly higher in eggs from Kiska Island than in eggs from the other islands. In contrast, polychlorinated biphenyl concentrations were higher in eggs from Adak, Amchitka, and Kiska (where military facilities have been installed) than in those from Tanaga (which has had little military activity). The most likely source of these contaminants in bald eagles was from their diets, which were variable spatially and temporally. Fish made up most (56%) of the eagles' diet on Adak and Tanaga Islands, followed by birds (25%) and mammals (19%). In contrast, birds comprised the majority (60%) of bald eagle diets on Amchitka and Kiska Islands, followed by mammals (30%) and fish (10%). The high proportion of seabirds in the diet of eagles from Kiska Island could be the major source of organochlorine and Hg contamination. Elevated concentrations of organochlorines in bald eagle eggs from the Aleutian Archipelago was surprising, because of the distance to agricultural areas. The results indicate that these contaminants can be transported long distances and affect wildlife populations in remote and pristine areas. We also discuss potential sources and transport mechanisms of these contaminants to the Aleutian Islands.

We assessed DNA repair and resistance to solar radiation in eggs of members of the western spotted frog complex (Rana pretiosa and R. luteiventris), species whose populations are suffering severe range reductions and declines. Specifically, we measured the activity of photoreactivating enzyme (photolyase) in oocytes of spotted frogs. In some species, photoreactivation is the most important mechanism for repair of UV-damaged DNA. Using field experiments, we also compared the hatching success of spotted frog embryos at natural oviposition sites at three elevations, where some embryos were subjected to ambient levels of UV-B radiation and others were shielded from UV-B radiation. Compared with other amphibians, photolyase activities in spotted frogs were relatively high. At all sites, hatching success was unaffected by UV-B. Our data support the interpretation that amphibian embryos with relatively high levels of photolyase are more resistant to UV-B radiation than those with lower levels of photolyase. At the embryonic stage, UV-B radiation does not presently seem to be contributing to the population declines of spotted frogs.