Explore the vast range of titles available.

Many forest-dependent animals require complex branch and bole structural features as substrates for nesting, and these features may take decades or centuries to develop. In young forests, lack of suitable nest substrates may limit occurrence and abundance of arboreal rodents. To test this hypothesis, we measured the response of arboreal rodents to installation of 429 artificial nest platforms at 17 young forest sites in the Coast Range of Oregon, United States. We compared the percentage of 100-m2 plots at sites containing nests before and after installation of nest platforms, and examined 5 a priori hypotheses of spatial patterns of use using logistic regression. One year after installation, we observed a 5.8-fold increase (95% CI = 2.4–9.2) in plots containing nests of red tree voles (Arborimus longicaudus) and a 2.9-fold increase (95% CI = 1.3–4.4) of tree squirrels (Glaucomys oregonensis, Tamiasciurius douglasii). In addition, we captured 37 adult red tree voles (30 females, 7 males). Presence of conspecific nests < 75 m away increased the odds of use by red tree voles but not by tree squirrels. Our results support the hypothesis that lack of suitable nest substrates limits occurrence of red tree voles in young forests, but results were ambiguous for tree squirrels. Increasing the availability of nest substrates via installation of nest platforms may increase abundance of red tree voles in young forests. However, we do not know if this will allow red tree voles to persist in young forests that are subjected to repeated commercial thinning and clear-cut harvesting.

Habitat suitability maps are important tools for conservation planning and species investigations, but maps at resolutions that are biologically meaningful and useful for local-level decision-making are lacking for many species that use resources at fine scales. Airborne light detection and ranging (LiDAR) describes 3-dimensional structure of forests and other habitats at high resolution, which can improve habitat models for many species and facilitate investigations otherwise impossible with field data or other remote-sensing techniques. We used an information-theoretic approach and logistic regression to model habitat of red tree voles (Arborimus longicaudus) at multiple spatial scales with predictors derived from airborne LiDAR in southwestern Oregon. We developed a priori models to evaluate habitat associations and identify good models useful for high-resolution mapping of habitat suitability across a large spatial extent. Our best models that compared habitats around nest trees of red tree voles to available sites performed well (i.e., accuracy = 0.83) on an independent test data set. We found fair performance in comparisons of habitat around nest trees to unused locations within areas previously identified as red tree vole habitat (i.e., accuracy = 0.71). Red tree vole nests were often in the largest trees in the stand and away from forest edges. Both analyses suggested that fine- and broad-scale predictors are important for modeling habitat of red tree voles. Habitat suitability for red tree voles should be predicted effectively by LiDAR acquisitions even with low point densities because maps were robust to reductions in point densities as low as 1 point/m². We found that LiDAR was effective for modeling habitat of red tree voles and expect it to improve performance of models for other species with similar habitat requirements.

Although herbivores rely on liver enzymes to biotransform plant secondary metabolites ingested in plant-based diets, only a few enzymes from a handful of species have been characterized at the genomic level. In this study, we examined cytochrome P450 2B (CYP2B) sequence diversity and gene copy number in a conifer specialist, the red tree vole (Arborimus longicaudus). We fed captive individuals exclusively Douglas-fir (Pseudotsuga menziesii) foliage, cloned and sequenced their liver CYP2B cDNA, and estimated CYP2B gene copy number. We identified 21 unique CYP2B nucleotide sequences, and 20 unique CYP2B amino acid sequences. Gene copy number of CYP2B was estimated at 7.7 copies per haploid genome. We compared red tree vole CYP2B with CYP2B sequences of a generalist, the prairie vole (Microtus ochrogaster), found in GenBank. Our study revealed that the CYP2B enzymes of red tree voles possess unique sequences compared to CYP2B enzymes of other herbivorous species. The unique combination of amino acid residues at key substrate recognition sites of CYP2B enzymes may underlie the ability of the red tree vole to specialize on a highly toxic diet of Douglas-fir.

Environmental regulations often require wildlife surveys prior to habitat disturbance to avoid impacts or as the basis for planning mitigation, yet project‐level surveys may not provide the insights needed to guide long‐term management. Management of the red tree vole ( Arborimus longicaudus ) has largely been based on such surveys. As an alternative approach, we evaluated distribution patterns using frequency of red tree vole occurrence and habitat suitability models to guide conservation planning. We developed a suite of models based on subsets of covariates from two previously developed models and evaluated the extent to which spatial covariates improved the models. We used presence–absence data that were collected from 364 randomly selected 1‐ha Current Vegetation Survey and Forest Inventory and Analysis plots to develop models and describe occurrence patterns. The best models included a spatial covariate, maximum tree diameter, distance from suitable habitat, forest age class, and the interaction between maximum tree diameter and forest age class. We compared performance of the previously published models, our best model, and an ensemble model that used predictions from all three models. Under the ensemble model, correct classification rates were relatively high and considerably improved, suggesting that the application of all three models provided greater accuracy than any individual model. We argue that habitat models, coupled with spatial patterns of the frequency of occurrence, can provide useful tools for addressing species management and may provide more insight than project‐level surveys. The use of habitat suitability models can therefore be closely tied to red tree vole management decisions and conservation strategies, as well as reducing survey costs that otherwise often make projects infeasible.

We sampled 86 randomly selected survey plots to evaluate the distribution and abundance of Red Tree Voles (Arborimus longicaudus) on the Tillamook and Clatsop State Forests in the northern Coast Ranges of Oregon in 2011–2013. We conducted surveys by visually searching for tree vole nests while walking along 500 m of transect in each plot. Trees with potential nest structures were climbed to determine if the structures were tree vole nests. We found tree vole nests in only 4 random plots, all of which were located near the coast, at the western edge of the Tillamook State Forest. Of 33 tree vole nests located, 20 (61%) were in old forests (≥80 y old), and 13 (39%) were in 1 plot in a young forest that was 65 y old. We concluded that tree voles were absent from most of the Tillamook and Clatsop State Forests, probably due to the fact that most of the area was either logged or burned in the early 1900s, and subsequently intensively managed on short rotations. We also suggest that remnant stands of old forest on Bureau of Land Management and state lands are acting as source populations from which tree voles populate adjacent young forests. Cuttings found in nests provided evidence that most of the voles were feeding on needles of Western Hemlock (Tsuga heterophylla) or Sitka Spruce (Picea sitchensis).

We studied consumption of free water by a sample of 7 Red Tree Voles (Arborimus longicaudus) maintained in captivity on a natural diet of Douglas-fir (Pseudotsuga menziesii) foliage. Mean consumption of free water by individual voles was 0.016 ± 0.001 ml/g/d, which is much lower than has been reported for most other species of voles. The small amount of free water consumed per day suggests that Tree Voles need little access to free water and can obtain nearly all of their water from their diet of conifer needles, which is low in caloric value but high in water content.

We examined patterns of size-associated morphological variation within the Red Tree Vole (Arborimus longicaudus) for the purposes of 1) identifying differences between the Red Tree Vole and the Dusky Tree Vole (A. l. silvicola), a putative subspecies of the Red Tree Vole; and 2) examining spatial patterns of morphological variation across the species' range. Our results illustrate subtle, but significant, morphological differences across the boundary that has been proposed to delimit the ranges of the Dusky Tree Vole and Red Tree Vole. However, the morphological characters examined have virtually no diagnostic utility for distinguishing between subspecies. We also performed a series of linear regressions that revealed correlations between morphological variation and latitude. Ultimately, these findings indicated that morphological variation in Red Tree Voles is in good agreement with Bergmann's Rule and Allen's Rule, 2 well-established ecographic principles that dictate relationships between environmental temperatures and morphological attributes. Because our analyses do not demonstrate strong differences between tree vole subspecies, we encourage future analyses of variation in pelage coloration and genetic structure to unequivocally determine the Dusky Tree Vole's status.

In 2003 to 2008, we conducted surveys to document the eastern and northern range limits of Red Tree Voles (Arborimus longicaudus) in the Columbia River Gorge and Hood River basin, Oregon. Our survey indicated the current range of the vole includes the area from Wahkeena Creek, 20 km east of Troutdale to Seneca Fouts State Park, 6 km west of Hood River. We also found a concentration of Red Tree Vole nests in the headwaters of the Lake Branch of Hood River, 27 km southwest of the town of Hood River. Of 70 vole nests located, 36 (52%) were old unoccupied nests with no evidence of recent use, 24 (34%) were unoccupied but had evidence of recent use as indicated by the presence of fresh green resin ducts or cuttings in the nest, and 10 (14%) were occupied by voles. Of the 70 vole nests, 74% were in forests dominated by mature or old-growth trees and 26% were in stands 25- to 60-y-old. This survey is the first to document the existence of Red Tree Voles in the upper Columbia River Gorge east of Cascade Locks. It also documents the occurrence of Red Tree Voles on the east slope of the Cascade Range in the headwaters of the Lake Branch of Hood River.