We analyzed demographic data from northern spotted owls (Strix occidentalis caurina) from 14 study areas in Washington, Oregon, and California for 1985-2003. The purpose of our analyses was to provide an assessment of the status and trends of northern spotted owl populations throughout most of their geographic range. The 14 study areas made up approximately 12% of the range of the subspecies and included federal, tribal, private, and mixed federal and private lands. The study areas also included all the major forest types that the subspecies inhabits. The analyses followed rigorous protocols that were developed a priori and were the result of extensive discussions and consensus among the authors. Our primary objectives were to estimate fecundity, apparent survival (/), and annual rate of population change (k) and to determine if there were any temporal trends in these population parameters. In addition to analyses of data from individual study areas, we conducted 2 meta-analyses on each demographic parameter. One meta-analysis was conducted on all 14 areas, and the other was restricted to the 8 areas that constituted the Effectiveness Monitoring Plan for northern spotted owls under the Northwest Forest Plan. The average number of years of reproductive data per study area was 14 (range ¼ 5-19), and the average number of recapture occasions per study area was 13 (range ¼ 4-18). Only 1 study area had ,12 years of data. Our results were based on 32,054 captures and resightings of 11,432 banded individuals for estimation of survival and 10,902 instances in which we documented the number of young produced by territorial females.The number of young fledged (NYF) per territorial female was analyzed by testing a suite of a priori models that included (1) effects of age, (2) linear or quadratic time trends, (3) presence of barred owls (Strix varia) in spotted owl territories, and (4) an even-odd year effect. The NYF varied among years on most study areas with a biennial cycle of high reproduction in even-numbered years and low reproduction in odd-numbered years. These cyclic fluctuations did not occur on all study areas, and the even-odd year effect waned during the last 5 years of the study. Fecundity was highest for adults (x¼0.372, SE¼0.029), lower for 2-year-olds (x¼0.208, SE¼0.032), and very low for 1-year-olds (x¼0.074, SE¼ 0.029). Fecundity was stable over time for 6 areas (Rainier, Olympic, Warm Springs, H. J. Andrews, Klamath, and Marin), declining for 6 areas (Wenatchee, Cle Elum, Oregon Coast Range, Southern Oregon Cascades, Northwest California, and Simpson), and slightly increasing for 2 areas (Tyee, Hoopa). We found little association between NYF and the proportion of northern spotted owl territories where barred owls were detected, although results were suggestive of a negative effect of barred owls on the Wenatchee and Olympic study areas. The meta-analysis on fecundity indicated substantial annual variability with no increasing or decreasing trends. Fecundity was highest in the mixed-conifer region of eas...
Barred Owls (Strix varia) have expanded their range throughout the ranges of Northern (Strix occidentalis caurina) and California Spotted Owls (S. o. occidentalis). Field observations have suggested that Barred Owls may be behaviorally dominant to Spotted Owls. Therefore, we conducted a test of behavioral dominance by assessing responsiveness of Spotted Owls to conspecific calls when they were in the simulated presence (i.e., imitation of Barred Owl vocalizations) of a Barred Owl. We hypothesized that Spotted Owls would be less likely to respond to conspecific calls in areas where Barred Owls were common. We used a binary 2 × 2 crossover experimental design to examine male Spotted Owl responses at 10 territories randomly selected within two study areas that differed in abundance of Barred Owls. We also conducted a quasi experiment at four study areas using response data from any Spotted Owl (male or female) detected following exposure to Barred Owl calls. We inferred from the crossover experiment that the simulated presence of a Barred Owl might negatively affect Spotted Owl responsiveness. Both subspecies of Spotted Owl responded less to Spotted Owl calls after exposure to Barred Owl calls, Northern Spotted Owls responded less frequently in areas having higher numbers of Barred Owls, and California Spotted Owls responded less frequently than Northern Spotted Owls overall.
Abstract. Spatial and temporal scales are important for understanding habitat associations because organisms have neither unbounded mobility nor perfect knowledge of their environment, but still must make decisions on where to seek food, shelter, and mates. Semi-aquatic turtles exemplify the need to evaluate potential habitat characteristics at a range of scales, because their ectothermy makes these animals particularly sensitive to local environmental conditions, yet their limited mobility spatially constrains selection of microsites. Microsite choice may also be sensitive to larger geographic context. We explored site occupancy and abundance of western pond turtles (Actinemys [Emys] marmorata) as a function of environmental variables over a range of spatial scales up to that of the entire watershed. We modeled occupancy at ponds and abundance at river sites using data from surveys conducted at 50 ponds and 58 river locations throughout the South Umpqua, Umpqua, and North Umpqua watersheds in western Oregon, USA in 1999-2000. The South Umpqua supported the greatest abundance of western pond turtles in rivers and the highest rates of occupancy in ponds. No turtles were detected in rivers of the North Umpqua, and only low numbers were detected in ponds in that watershed. Increasing amount of potential relative solar radiation was associated with increased probability of pond occupancy, particularly in the North Umpqua watershed. Pond turtle abundance in rivers increased with increasing distance to nearest pond, decreasing area of nearby ponds, and increasing area of nearby wetland habitat of all types, particularly in the Klamath Mountain and Coast Range physiographic provinces, which dominate the South Umpqua and Umpqua watersheds, respectively. Western pond-turtle occupancy and abundance varied with both broadscale and fine-scale habitat features, not solely to the fine-scale features that are most often measured.
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