Northeastern Oregon Research Articles

Nest success and cause‐specific nest failure of grassland passerines breeding in prairie grazed by livestock

AbstractLivestock grazing is a widespread source of habitat modification, and may affect populations of ground‐nesting grassland birds by influencing rates of nest failure. Nesting attempts can fail for various reasons, and determining risk of failure from specific causes associated with livestock grazing would enhance development of range management practices in areas managed for threatened grassland bird populations. Domestic livestock may influence nest failure by affecting vegetation structure, numerical or functional responses of predators, or directly by trampling nests. We hypothesized stocking rate may influence nest fate because it affects the amount and distribution of remaining vegetation, and the number of large herbivores to which nests are exposed. In 2007 and 2008, we evaluated nest fates for savannah sparrows and horned larks under 4 stocking rates experimentally applied in 40‐ha paddocks in northeastern Oregon, USA. In addition to stocking rate, we evaluated variables such as vegetation structure and predator abundance and activity to help clarify mechanisms responsible for nest failure. We used a discrete competing risks framework to estimate daily probability of nest survival and failure from specific causes. These algorithms, implemented in a stand‐alone graphical user interface‐driven model, allow incorporation of covariates within an information theoretic approach to model inference. Although stocking rate influenced vegetation structure, the only nest failures related to stocking rate were from trampling. Trampling events were too infrequent to test for treatment effects (only 1 nest of each species), but occurred in the moderate and high stocking treatments. Additional variables were related to variation in nest failure from predation, but we found no support for the hypothesis that these causes of failure were affected by stocking rate. For savannah sparrows, daily probability of nest success (95% CI) = 0.97 (0.96–0.98); predation = 0.018 (0.008–0.028); and trampling = 0.001 (0.000–0.004). For horned larks, daily probability of nest success = 0.96 (0.95–0.98); predation = 0.029 (0.012–0.045); and trampling = 0.003 (0.000–0.007). Our results suggest grasslands managed for livestock may generally be compatible with grassland songbird conservation, at least for the species and stocking rates examined here. The most effective conservation strategies for improving nest success will involve decreasing risk of nest predation. However, we found no evidence that management of stocking rate is an effective method for doing so. © 2012 The Wildlife Society.

Environmental correlates of signal crayfish, Pacifastacus leniusculus (Dana, 1852), density and size at two spatial scales in its native range

ABSTRACT While much literature exists on the ecology and ecosystem impacts of signal crayfish, Pacifastacus leniusculus (Dana, 1852), as an invasive species, little information exists on the ecology of this species in its native range in the Pacific Northwest, USA. Signal crayfish (P. leniusculus leniusculus) were collected from the Umatilla River in northeastern Oregon, USA, where they are native. Collecting occurred during the summer at 13 sites spanning the longitudinal gradient of the river to examine the relationship between density and size of individuals and environmental factors at two spatial scales. At the reach scale (100+ m2) the density of young-of-year (YOY), and age 1+ female and male crayfish was positively associated with substrate size. Additionally, age 1+ female and male crayfish density was negatively associated with the amount of crop agriculture. Substrate size was also important in determining the density and size of crayfish at the microhabitat scale (<1 m2) with greater densities...

Seasonal Movement and Distribution of Fluvial Adult Bull Trout in Selected Watersheds in the Mid-Columbia River and Snake River Basins

From 1997 to 2004, we used radio telemetry to investigate movement and distribution patterns of 206 adult fluvial bull trout (mean, 449 mm FL) from watersheds representing a wide range of habitat conditions in northeastern Oregon and southwestern Washington, a region for which there was little previous information about this species. Migrations between spawning and wintering locations were longest for fish from the Imnaha River (median, 89 km) and three Grande Ronde River tributaries, the Wenaha (56 km) and Lostine (41 km) rivers and Lookingglass Creek (47 km). Shorter migrations were observed in the John Day (8 km), Walla Walla (20 km) and Umatilla river (22 km) systems, where relatively extensive human alterations of the riverscape have been reported. From November through May, fish displayed station-keeping behavior within a narrow range (basin medians, 0.5–6.2 km). Prespawning migrations began after snowmelt-driven peak discharge and coincided with declining flows. Most postspawning migrations began by late September. Migration rates of individuals ranged from 0.1 to 10.7 km/day. Adults migrated to spawning grounds in consecutive years and displayed strong fidelity to previous spawning areas and winter locations. In the Grande Ronde River basin, most fish displayed an unusual fluvial pattern: After exiting the spawning tributary and entering a main stem river, individuals moved upstream to wintering habitat, often a substantial distance (maximum, 49 km). Our work provides additional evidence of a strong migratory capacity in fluvial bull trout, but the short migrations we observed suggest adult fluvial migration may be restricted in basins with substantial anthropogenic habitat alteration. More research into bull trout ecology in large river habitats is needed to improve our understanding of how adults establish migration patterns, what factors influence adult spatial distribution in winter, and how managers can protect and enhance fluvial populations.

Sixty-Seven Years of Landscape Change in the Last, Large Remnant of the Pacific Northwest Bunchgrass Prairie

The Zumwalt Prairie in northeastern Oregon is the last large remnant of the Pacific Northwest Bunchgrass Prairie. Compared to other prairies in North America, relatively little is known about these arid temperate grasslands as the majority disappeared quickly after Euro-American settlement. In this paper we describe the landscape history of the Zumwalt Prairie through interpretation of historical aerial photos. Beginning with photos taken in 1938, we examined photos for area of cultivation and woody vegetation and number of buildings and stock ponds. Using data collected in 1976 and 2001, area of woody vegetation was further classified as aspen (Populus tremuloides, Michx.), conifers, and shrubs for analysis of trends. Area in cultivation and number of buildings decreased over the 67 years we examined. In contrast, the number of stock ponds increased. Overall, the area of woody species increased over the period of study; area of aspen declined while acreage of conifers and shrubs increased. The land cover and land-use changes observed on the Zumwalt Prairie reflect the complex social and economic changes that have occurred since Euro-American settlement began in the late nineteenth century.

Magma emplacement process zone preserved in the roof of a large Cordilleran batholith, Wallowa Mountains, northeastern Oregon

The crestal portion of the upper-crustal Wallowa batholith, northeastern Oregon, provides an exceptional three-dimensional section through a flat batholith roof which rolls over into a steep wall at elevations of about 1600–2800m. The roof–batholith margin is interpreted as representing the ‛frozen-in’ process zone of granodiorite magma which was arrested during its ascent, thus providing a direct view into processes that operate during construction of large, shallow-level Cordilleran-type batholiths. The batholith host rock records two principal and presumably coeval emplacement processes: ductile flow largely accommodated by rheologically weak and thus severely deformed marbles in the steep wall, and voluminous stoping of rheologically stronger, bedded siliciclastic rocks along the flat roof. Structures preserved along the roof suggest that the stoping was a multi-stage process involving emplacement of up to hundred meters long sills along bedding planes and formation of short connecting dikes cutting across bedding to produce sill–dike networks along the batholith–roof contact. Portions of the sill–dike networks and enclosed large rectangular roof blocks were then stoped into and continued to be mechanically disintegrated in the magma chamber. This inferred mechanism departs from the commonly assumed mode of stoped block formation solely by thermal shattering. In our view, host rocks in the process zone are fractured by dike propagation. It follows that such process of roof disruption and subsequent block stoping could be extremely rapid. In combination with other processes (e.g., roof uplift, ductile flow in weak lithologies), such rapid stoping could contribute to emplacement of voluminous and mostly non-sheeted Cordilleran-type batholiths at upper crustal levels.

Pollination Biology ofPotentilla recta(Sulfur Cinquefoil) and Its Cooccurring Native CongenerPotentilla gracilisin Northeastern Oregon

Pollination biology of the invasive plant sulfur cinquefoil (Potentilla rectaL.) and it's native cooccurring congener slender cinquefoil (P. gracilisDougl. ex. Hook.) was studied from 2002–2004, at four sites in northeastern Oregon, USA The native cinquefoil flowered first for five weeks, followed by the invasive for five weeks, with two weeks overlap in mid-June. Invasive flowers attracted 74 species and 543 individuals; the native attracted 93 species and 619 individuals. The most important pollinators for the invasive, in order of importance, were:Apis mellifera,Ceratina nanula,Halictus tripartitus,Lasioglossum sisymbrii, andBombus rufocinctus; for the native:C. nanula,Trichodes ornatus,H. ligatus,L. sisymbrii, andL. olympiae. The invasive produced higher numbers of seeds per plant, having greater mass per unit vegetation. Mean seed size was lower for the invasive when pollinators were allowed access to flowers, but seed size increased linearly with more complete exclusion of pollinators; the native showed no such response to pollinator exclusion. Compared to the native, nearly twice as many seeds germinated for sulfur cinquefoil (35.0% versus 19.5%), with seeds germinating over a longer period of time. Results are discussed as they relate to the invasiveness of sulfur cinquefoil relative to the native.

Population Dynamics of the Beet Leafhopper in Northeastern Oregon and Incidence of the Beet Leafhopper-Transmitted Virescence Agent Phytoplasma

Beet leafhoppers were collected weekly on yellow sticky traps placed at 36 locations in Morrow and Umatilla Counties in northeastern Oregon in April through November 2007, 2008, and 2009. Insects were counted, collected, and a subset of the insects was tested for the presence of the beet leafhopper-transmitted virescence agent phytoplasma, the causal agent of potato purple top disease in this region. Beet leafhoppers were present throughout the sampling period and the number of insects collected peaked in June of each year with smaller peaks in July and October. Of the 804 insects tested for phytoplasma in 2007, 2008, and 2009, 21, 18, and 22% tested positive for phytoplasma, respectively. Most of the phytoplasma-positive insects were collected from mid-June through July. Positive insects, however, were collected as late as 13 November in 2007 and 2008. These data indicate that a relatively high proportion of the beet leafhoppers in this area are harboring the phytoplasma. Therefore, the potential for development of purple top disease of potatoes from migrating beet leafhoppers in this important potato producing region is quite high and measures to control this pest throughout the growing season are probably necessary in order to reduce disease pressure.

DETRITAL RECORD OF UPPER TRIASSIC REEFS IN THE OLDS FERRY TERRANE, BLUE MOUNTAINS PROVINCE, NORTHEASTERN OREGON, UNITED STATES

We report a coral-sponge dominated reef lithofacies in detrital boulders of carbonate-clast conglomerate from the Olds Ferry terrane, Blue Mountains Province, Willow Spring locality, northeastern Oregon. This discovery constitutes the first report of Triassic reefal lithofacies from the Olds Ferry terrane. Corals at the site include a high-growing, dendroid-phaceloid species that acted as a framework or sediment baffle, and a low-growing, cerioid, encrusting coral and a sponge that acted as sediment binders. The co-occurrence of coral taxa in the Wallowa intraoceanic arc and Olds Ferry pericratonic arc terranes suggests that during the Late Triassic, these regions were in proximity to one another. With this report, Upper Triassic carbonate rocks are known from all of the major terranes of the Blue Mountains Province and a Tethyan affinity is established for the fauna of the Olds Ferry terrane. We suggest that the source of this Late Triassic coral-sponge reef fauna in the upper member of the Huntington Formation was intrabasinal and that the source rocks are no longer exposed in the region. Numerous possible regional source areas for these detrital limestone clasts rule out the need to call upon an exotic terrane source area.

Potential for ethanol production from conservation reserve program lands in Oregon

Increase in energy demand has led towards considering lignocellulosic feedstocks as potential for ethanol production. Aim of this study was to estimate the potential of grass straws from conservation reserve program (CRP) lands as feedstocks for ethanol production. The CRP was initiated to ensure reduction in soil erosion with a concomitant improvement in water quality and aquatic habitats. Species and abundance of various grasses in CRP sites can vary substantially. Ethanol yield from biomass is directly correlated to sugar content among other factors. It therefore becomes important to study the variability in the biomass composition from different CRP sites to reliably estimate biofuel production potential. Grass samples were collected from five fields contracted to CRP in Umatilla County in Northeastern Oregon. Composition of these samples was experimentally determined and was statistically verified to be similar for most of the sites. Sugar content was highest (60.70%) and statistically different for only one site (CRA 8.2). Our results suggest that biomass harvested from different sites did not significantly vary in terms of their chemical composition and therefore could be used in a single integrated process to produce bioethanol. Total potential ethanol yield from various CRP lands in Oregon, assuming a 10 yr harvesting frequency, was estimated to be 40 × 106 l of ethanol (28.5–53.7 × 106 l/yr) with current management practices subject to other constraints.

Bird community responses to cattle stocking rates in a Pacific Northwest bunchgrass prairie

In 2006–2010, effects of four different cattle stocking rates (0, 14.4, 28.8, and 43.2 animal unit months) were compared, representing 0%, 20%, 32%, and 46% utilization of vegetation by domestic livestock, on vegetation structure (as indexed by visual obstruction), and songbird population and apparent nest density, community composition, and diversity in a Pacific Northwest bunchgrass prairie in northeastern Oregon, USA. Overall paddock-level visual obstruction decreased and structural heterogeneity increased with increasing stocking rates, and those effects carried over 1 year after grazing had ceased. Most species were able to locate nesting sites regardless of differences in visual obstruction, except western meadowlark and vesper sparrow, for which obstruction was lower in paddocks with higher stocking rates. Apparent nest density for grasshopper sparrows was negatively affected by higher stocking rates. Grazing effects on absolute songbird population density were restricted to negative effects of higher stocking rates on savannah sparrows, but this relationship was not observed until 1 year after grazing had ceased. Songbird community composition differed between control and heavily-grazed paddocks, driven by an increase in the proportion of horned larks and a decrease in the proportion of savannah sparrows in heavily-grazed paddocks from pre-treatment to post-treatment years. Bird diversity indices were unaffected by stocking rate. Negative effects of high stocking rates on densities of two species and the absence of any clear positive effect for the other three species suggest high stocking rates as applied in this experiment may not provide suitable habitat for all grassland songbirds. The absence of negative responses of density to low and moderate stocking rates suggests these grazing regimes generally provided suitable habitat for all species.

Magnetic fabric of Late Jurassic arc plutons and kinematics of terrane accretion in the Blue Mountains, northeastern Oregon

The Blue Mountains Province of northeastern Oregon, western Idaho, and southeastern Washington (USA) consists of the amalgamated Wallowa distal island arc, Baker mélange-bearing accretionary wedge–forearc, and Olds Ferry fringing island arc terranes. Anisotropy of magnetic susceptibility (AMS) and particularly the orientation of magnetic lineations in Middle to Late Jurassic diorite–tonalite–granodiorite plutons intruding the Baker terrane indicate a change in tectonic regime from flattening with principal stretching at a high angle to the local orientation of the terrane boundaries at around 160Ma to constriction with boundary-subparallel subhorizontal stretching at ca. 146Ma. The former magnetic fabric is compatible with magnetic lineations recording strain related to top-to-the-southwest back-thrusting onto the Olds Ferry arc. In contrast, the ~146Ma boundary-parallel stretching may record strain partitioning whereby a part of the Baker terrane was extruded laterally parallel to terrane boundaries after the terrane collision. After restoration for the clockwise post-mid-Cretaceous terrane rotation, the ~160Ma restored principal stretching directions are compatible with the overall left-oblique subduction and convergence of the Wallowa distal and Olds Ferry fringing arc terranes. Magnetic fabric data from the plutons thus support the interpretation that the early displacement of the Blue Mountains Superterrane, and perhaps also its possible correlative Intermontane Superterrane of the Canadian Cordillera, was southward along the truncated North American continental margin during the late Middle Jurassic.

Birth-site selection and predation risk of Rocky Mountain elk

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.

Temporal changes in age and sex ratios of forest grouse harvested in northeastern oregon

AbstractRatio of immature (young of the year) grouse to adult birds (I:A) in the harvest of upland game birds is commonly used as an index to annual reproduction; however, I:A ratios can vary as the season progresses producing biased estimates. We analyzed I:A ratios in the daily harvest of dusky grouse (Dendragopus obscurus) and ruffed grouse (Bonasa umbellus) in northeastern Oregon over 28 years (1981–2008) and found that I:A ratios in the harvest declined for both species as the hunting season progressed. We also analyzed ratios of adult female to adult male (AF:AM) grouse to determine if female and male grouse were harvested in equal numbers throughout the harvest season. We found that more males than females of both species were harvested, but that AF:AM ratio of both dusky and ruffed grouse did not change during most of the hunting season. Approximately 50% of the annual harvest occurred during the first 14 days of the hunting season. Therefore, we recommend using the ratios of I:A birds in the first 14 days of the harvest season as the best index to annual reproduction of forest grouse in northeast Oregon. © 2011 The Wildlife Society.

Interactions between macroinvertebrate taxa and complex environmental gradients influencing abundance and distribution in the Umatilla River, Northeastern Oregon

Non-parametric multiplicative regression was used to develop regression models for six macroinvertebrate genera present in the Umatilla River in northeastern Oregon. For all taxa, elevation, turbidity, and conductivity were identified as predictors. They described between 25.5% and 63.4% of the variation in the abundance of the six taxa. Sensitivity analysis of the parameters showed the relative importance of the model parameters as predictors of abundance, with conductivity having a broader range of sensitivity values than either elevation or turbidity. Daily average temperature, percentage of algal cover, depth, and width were also shown to be possible predictors of taxa abundance. As all the variables examined in this study are potentially impacted by non-target effects of agriculture in rivers, these results indicated that agriculture disturbance in the adjacent landscape affects the abundance and distribution of benthic indicator taxa.

Early Mesozoic paleogeography and tectonic evolution of the western United States: Insights from detrital zircon U-Pb geochronology, Blue Mountains Province, northeastern Oregon

This study assesses early Mesozoic provenance linkages and paleogeographic tectonic models for the western United States based on new petrographic and detrital zircon data from Triassic and Jurassic sandstones of the Izee and Olds Ferry terranes of the Blue Mountains Province, northeastern Oregon. Triassic sediments were likely derived from the Baker terrane offshore accretionary subduction complex and are dominated by Late Archean (ca. 2.7–2.5 Ga), Late Paleoproterozoic (ca. 2.2–1.6 Ga), and Paleozoic (ca. 380–255 Ma) detrital zircon grains. These detrital ages suggest that portions of the Baker terrane have a genetic affinity with other Cordilleran accretionary subduction complexes of the western United States, including those in the Northern Sierra and Eastern Klamath terranes. The abundance of Precambrian grains in detritus derived from an offshore complex highlights the importance of sediment reworking. Jurassic sediments are dominated by Mesozoic detrital ages (ca. 230–160 Ma), contain significant amounts of Paleozoic (ca. 290, 380–350, 480–415 Ma), Neoproterozoic (ca. 675–575 Ma), and Mesoproterozoic grains (ca. 1.4–1.0 Ga), and have lesser quantities of Late Paleoproterozoic grains (ca. 2.1–1.7 Ga). Detrital zircon ages in Jurassic sediments closely resemble well-documented age distributions in transcontinental sands of Ouachita-Appalachian provenance that were transported across the southwestern United States and modified by input from cratonal, miogeoclinal, and Cordilleran-arc sources during Triassic and Jurassic time. Jurassic sediments likely were derived from the Cordilleran arc and an orogenic highland in Nevada that yielded recycled sand from uplifted Triassic backarc basin deposits. Our data suggest that numerous Jurassic Cordilleran basins formed close to the Cordilleran margin and support a model for moderate post-Jurassic translation (∼400 km) of the Blue Mountains Province.

A new Aphidius Nees (Hymenoptera, Braconidae, Aphidiinae) of Ericaphis fimbriata (Richards) (Hemiptera, Aphididae) and key to parasitoids of blueberry aphid in the Pacific Northwest

Aphidius ericaphidis Pike &amp; Starý, sp. nov., is described and illustrated. This aphidiine is a parasitoid of the blueberry aphid, Ericaphis fimbriata (Richards), widely found associated with the commercial highbush blueberries, Vaccinium corymbosum L., in southwestern British Columbia, Washington, and in northeastern Oregon. It is one of several species of aphidiines known to attack E. fimbriata in North America. A key is provided to distinguish it from other parasitoid species of E. fimbriata.

Plant Community Development in a Dryland CREP in Northeastern Oregon

Riparian areas in dryland crop regions of the Intermountain Pacific Northwest have largely been converted to cropland or pasture during the last 140 years. Some formerly cultivated floodplains have become difficult to farm; enrollment of these lands into conservation programs provides the opportunity to use them as wildlife habitat and as buffer areas near streams. Our objective was to evaluate plant community development on an USDA Conservation Reserve Enhan- cement Program site in northeastern Oregon from when the plant was planted in 1999 through 2008. The research was designed as a descriptive study. We established permanent line-transects to quantify vegetation establishment and changes in species composition through time. We collected data in 2000-2001 and 2007-2008. Vegetation cover in 2000-2001 was 100%, dominated by tall wheatgrass. Living plant material cover decreased from 98% in 2000-2001 to 33% in 2007 and 68% in 2008; dead plant residue significantly increased and tall wheatgrass cover decreased. Native species were present in similar percentages from 2000 to 2008, although there was a shift from target to nontarget species. The 1999 seeding can be judged a success because of the ground cover provided and the establishment of one target species, tall wheatgrass. However, the increased ratio of dead to living plant material and shift to non-target annual weed species suggests that more active management (i.e., fire, grazing, or mowing) of the tall wheatgrass stand is needed to maintain its productivity and/or a healthy mix of multiple species.

Intensive Crop Rotation Yield and Economic Performance in Minimum Tillage and No Tillage in Northeastern Oregon

In the intermediate annual precipitation zone (14 to 18 inches) of northeastern Oregon, there is interest in increasing the intensity of cropping with spring crops. Mechanical tillage remains popular for seedbed preparation and weed control, but contributes to environmental problems and high labor and fuel cost. No-tillage (NT) crop production can reduce on site and off site problems and has lower labor and fuel costs, but soil-borne disease and weed control problems can limit yields. We compared crop yields, production costs, and economic returns of an intensive, four-year crop production rotation under two management systems: (i) minimum tillage (MT) with cultivation by chiseling, sweeping, and rod weeding; and (ii) NT with chemical weed control. The rotation was fallow-winter wheat-dry spring pea-winter wheat in which a spring broadleaf crop is included to aid in the control of winter annual weeds and reduce host pathogen levels of soil-borne cereal diseases. Four year averages of wheat yields in the NT treatment were equal to or greater than those in the MT treatment whereas dry green pea production was roughly equal in each treatment. Crop productivity differed significantly in each phase of the rotation in descending order from winter wheat following fallow [4,578 lb/acre (76 bu/acre)], winter wheat following dry spring pea [3,548 lb/acre (59 bu/acre)], to dry spring pea (1,505 lb/acre). Partial budget analysis shows that NT is substantially less costly than MT in terms of labor and fuel, potentially making NT economically viable for intensive cropping systems in the intermediate precipitation dryland region of northeastern Oregon.

The Status of the ‘Red-Listed’Bombus occidentalis(Hymenoptera: Apiformes) in Northeastern Oregon

Abstract The western bumble bee, Bombus occidentalis, is included on the red list of bees by The Xerces Society. It was once a common bumble bee west of the Cascades but in the late 1990s it experienced a dramatic decline along coastal regions. The cause was speculated to be due to the introduction of pathogens from captive-bred bumble bees used for pollination of greenhouse crops. In extensive surveys conducted in western and southern Oregon, 10 individuals have been recorded since 2000. In this note, we report the collection of 49 individual B. occidentalis over two years in the Zumwalt Prairie Preserve of northeastern Oregon. This finding shows that B. occidentalis persists in northeastern regions of the Pacific Northwest, either because of geographic isolation from or potential resistance to the pathogens that decimated populations in the western part of the region. Further research is needed to determine its occurrence in other regions of its historical range to assess the extent of its decline. In a...

Thermoregulatory Mechanisms Used in a Maternity Colony Of Townsend's Big-Eared Bats in Northeastern Oregon

As natural roosts of Big-ear Bats (Corynorhinus townsendii ssp.) are threatened or disappear, artificial roosts offering an acceptable microclimate may become an important component of the conservation strategy for this species. To determine how microclimate affects roosting behavior, I studied the responses of a maternity colony of Townsend's Big-eared Bats (C. t. townsendii) to varying temperature and humidity conditions in an attic roost. I constructed matrices of ambient temperature (Ta) and humidity from data logger recordings. I used a thermal imaging system to image the colony at 4 times on each of 4 days during the lactation period, recording size and location of each cluster or solitary individual. Clustering where it was warmest and apparent vasoconstriction of blood vessels in the ears were used to reduce heat loss at low Ta. Reduced clustering, movement to cooler locations, apparent vasodilation of blood vessels in the ears, and increased resting were used to increase heat dissipation at high Ta. The mechanisms used at both low Ta and high Ta probably also reduced metabolic rate and heat production. Humidity did not appear to affect cluster size and location. These results suggest that large, open-room structures offering a range of Ta and enough space for bats to spread apart would be important characteristics of artificial roosts for maternity colonies of C. t. townsendii.