Stephen D. West

Associations of bats with local structure and landscape features of forested stands in western Oregon and Washington

Abstract Understanding the processes that underlie bat distribution and activity patterns requires examination of habitat associations at multiple scales. We examined the association of both local structure and landscape context with bat activity in forested stands using ultrasonic detectors. Forty-eight stands in western Oregon and Washington were monitored for bat activity on at least six occasions for each of two field seasons. At the stand level, bat activity was negatively associated with tree density. The standard deviation of tree density and the density of newly created snags were positively associated with bat activity. In combination, these three variables explained 46% of the total variance in bat activity among stands. Landscape-level variables did not explain any significant variation among a subset of stands (n=22). Our study suggests that management of forest-dwelling bats should focus primarily on structural attributes at the stand level and the effects of these features on feeding and roosting opportunities.

The Influence of Regional Climate and Nightly Weather Conditions on Activity Patterns of Insectivorous Bats

We examined the influence of average climatic conditions and nightly weather variations using bat detectors on the summer activity of bats. Average summer precipitation was the principal climate variable correlated with differences in bat activity along a latitudinal array of sites, with the highest activity levels occurring at sites located in montane rain shadows. On a nightly basis, the occurrence of rain and low temperatures had strong negative correlations with flight activity. However, the variation in nightly activity at a site that was explained by weather was relatively small. Our results suggest that the use of long-term climatic data offers potential to predict variations in bat activity among sites. Such information may be useful in recognizing conservation priorities for the management of bats in the Pacific Northwest where topography is complex and climate conditions are variable.

Dynamics of Colonization and Abundance in Central Alaskan Populations of the Northern Red-Backed Vole, Clethrionomys rutilus

Population dynamics of Clethrionomys rutilus and Microtus oeconomus were examined during colonization of a severely burned (July 1971) area of black spruce forest, located 40 km north of Fairbanks, Alaska. Livetrapping from June 1972 to September 1976 on two trapping grids, one in burned and the other in unburned forest, revealed that colonization of the burned area by Clethrionomys was gradual, characterized by midwinter abandonment until food and cover resources were sufficient to allow overwintering in 1975, four years after the fire. Reproduction did not occur on the burned area during the first two post-burn years. Despite establishment of a resident population in 1975, recruitment was dependent upon immigrant voles, particularly pregnant females. A high rate of immigration into recently burned areas, and hence successful colonization, is possible for Clethrionomys because source populations exist in all areas of mature forest. Microtus oeconomus , captured only twice on the unburned area, arrived on the burned area in 1974, three years after the fire. However, Microtus density was low, and the population consisted primarily of transient voles. Clethrionomys density underwent a simple sequence of annual fluctuations. In unburned forest, peak density, variable from year to year, was reached in the fall, and low densities occurred yearly in early summer. Density was high in 1974 and 1975, low in 1972, 1973, and 1976. High 1974 and 1975 densities were due to increased reproductive output, especially of first generation (spring-born) females. Stomach content analysis indicated that Clethrionomys relied heavily upon the fruits of several berry-producing plants in all seasons. The phenology of central Alaska fruit production results in fruit scarcity in early summer; it is hypothesized that this variable strongly influences population density each year and perhaps the amplitude of the annual cycle of abundance.

Seasonal Variability in the Use of Space by Western Gray Squirrels in Southcentral Washington

A lack of quantitative information on life history of the western gray squirrel (Sciurus griseus) has hampered conservation and management efforts across its range. We report on data from 21 squirrels radiotracked in Klickitat County, Washington, from 1998 to 1999 to examine the interaction between home-range size, sex, and season. Home-range estimates were calculated by using minimum convex polygon and fixed kernel methods. Only adult animals with � 40 relocations were included in total home-range comparisons. Estimates of 95% minimum convex polygon home range in Washington averaged 73.0 ha for males (n ¼ 9) and 21.6 ha for females (n ¼ 12) for year-round use, significantly larger than those from Oregon and California. Differences in homerange size of males and females were significant. Fixed kernel and minimum convex polygon estimates were similar in size. We suggest that near the northern limit of the species’ geographic range low species richness, low abundance, and a patchy distribution of mast-producing vegetation result in large male and female home ranges, low overlap of female home ranges, and a sparsely distributed squirrel population.

Nest Site Selection by Western Gray Squirrels at Their Northern Range Terminus

Abstract The western gray squirrel (Sciurus griseus) in Washington, USA, is limited to 3 disjunct areas and is a state threatened species. Information is lacking for the North Cascades population, which is the northernmost population for the species. Squirrels in this population exist without oaks (Quercus spp.) that provide forage and cavities for maternal nests elsewhere in their range. During May 2003 to August 2005, we studied selection of nest sites and nest trees by 18 radiocollared squirrels in Okanogan County, Washington. Without oak cavities, females reared their young in dreys. General nest-tree characteristics were similar to characteristics of western gray squirrel nest trees in Southeastern Cascades: relatively tall ponderosa pines (Pinus ponderosa) ≥40 cm diameter at breast height. Results from conditional logistic models determined that the odds of a squirrel selecting a tree for nesting increased with greater diameter at breast height and with infection by dwarf mistletoe (Arceuthobium spp.). Nest sites with high selection probability by squirrels had greater basal area and number of tree species than available unselected sites. Retention of forest patches that include a mix of conifer species or conifer and deciduous trees and moderate to high basal area could promote nesting opportunities, connectivity for arboreal travel, as well as abundance and diversity of hypogeous fungi. Experiments to test the efficacy of retaining untreated patches of varying size (including trees infected with mistletoe) on nesting by western gray squirrels within stands managed for fire suppression and forest health would provide important information about the effects of forest fuel management on arboreal wildlife.

Cheatgrass (Bromus tectorum) dominates cheek pouch contents of the great basin pocket mouse (Perognathus parvus).

ABSTRACT . Most of the native shrubsteppe habitat in the northern Columbia Basin of eastern Washington has been invaded by cheatgrass (Bromus tectorum) or converted to agricultural lands. Therefore, ecological patterns and dynamics on native shrubsteppe and reestablished grasslands are of high conservation interest. We analyzed the cheek pouch contents of Great Basin pocket mice (Perognathus parvus) from 48 study sites in this region to quantify seed collection by this species and to determine the influence of habitat type on cheek pouch seed contents. In all 3 habitat types-newly established Conservation Reserve Program (CRP) lands, older CRP lands, and shrubsteppe-B. tectorum constituted the majority of seeds collected from the cheek pouches. Mean generic richness of collected seeds was higher in shrubsteppe than in new CRP habitats. On average, females collected a greater number of seed genera than males did, and pocket mice collected more seed genera as the autumn season progressed. Exotic B. tectorum has become the most frequently collected autumn food resource for pocket mice in the northern Columbia Basin.

Bat Activity and Species Occurrence on the Hanford Site in Eastern Washington

Although bats are a group with high species richness in shrub-steppe areas of the Columbia Basin, limited information is available on distributions, species occurrence, and habitat use. We surveyed bat populations of the Hanford Site, which has provided a refuge for shrub-steppe flora and fauna in Washington State. We used Anabat detectors, harp traps, mist nets, and auditory-visual observations during 1997 and 1998 to document the occurrence of bat species and to compare activity levels among major habitat types on the site. Across both years, we recorded 6,470 bat calls during 302 bat detector survey-nights at 66 locations. Bats of the genus Myotis constituted 84 to 88% of total calls each year. The hoary bat (Lasiurus cinereus), silver-haired bat (Lasionycteris noctivagans), western pipistrelle (Pipistrellus hesperus), big brown bat (Eptesicusfuscus), and pallid bat (Antrozous pallidus) also were recorded. Big brown bats have not been reported previously at the Hanford Site. Detection rates were highest near potential roosting structures and riparian foraging areas, and lowest in upland shrub-steppe cover types. During 133 trap nights across both years, we captured 81 bats of 5 species: the western smallfooted myotis (Myotis ciliolabrum), little brown myotis (M. lucifugus), Yuma myotis (M. yumanensis), silver-haired bat, and pallid bat. The site supports at least 3 arid-land bats (western small-footed myotis, western pipistrelle, and pallid bat) that are near the northern edge of their species distributions. By protecting large patches of undisturbed habitat, the Hanford Site has helped maintain a diverse bat fauna in Washingtons shrub-steppe. In addition, some habitat modifications at the site may have benefited bats, as evidenced by heavy use of old buildings, irrigation run-off wetlands, and planted trees.

A Record of the Spotted Bat (Euderma maculatum) from Crescent Bar, Washington

bia, Idaho, and Oregon (Watkins 1977; Nagorsen and Brigham 1993; Verts and Carraway 1998). Sarell and McGuinness (1993) presented the first reports of spotted bats in north-central Washington State. Subsequent surveys have noted spotted bats at additional locations, including sites in Douglas, Grant, and Okanogan counties (John Fleckenstein, Natural Heritage Program, Washington Department of Natural Resources, Olympia, WA, pers. comm.; Neal Hedges, Bureau of Land Management, Wenatchee, WA, pers. comm.). However, limited information is available about the distribution

Occurrences of the Coast Mole (Scapanus orarius orarius) in the Southern Washington Cascades

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