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We used a combination of capture and acoustic monitoring equipment to examine use of habitat by bats in a desert riparian community in southern Nevada. Each habitat type (riparian marsh, mesquite bosque, riparian woodland, and riparian shrubland) was simultaneously and continuously sampled acoustically in 3- to 5-night increments for 54 nights between June 2000 and January 2001. Fifteen species of bats were detected acoustically, 13 of which were captured using harp traps or mist nets. Five species were not detected frequently enough to be included in statistical analyses. California leaf-nosed bats (Macrotus californicus) and Brazilian free-tailed bats (Tadarida brasiliensis) were generalists, spending equal amounts of time in each habitat. Western yellow bats (Lasiurus xanthinus) and pallid bats (Antrozous pallidus) demonstrated strong biases for riparian woodland over the other habitats sampled. The remaining 6 species spent substantially more time in at least 1 of the 4 habitats. Riparian woodlands accounted for more than 50% of all bat activity, whereas riparian marshes were the least used habitat. High species richness and differences in habitat use by most species emphasizes the importance of a diversity of riparian habitats for bats at the study site. The existence of both native and nonnative habitat may elevate bat species richness and increase the degree of differential habitat use to levels higher than would be expected if only native habitat existed at the study site. Understanding differential riparian habitat use by bats in desert ecosystems may have profound management implications.

The first record of western yellow bat (Lasiurus xanthinus) for Nevada was found at the Moapa Valley National Wildlife Refuge, Muddy River, Clark County in January 1999. Year-round residence and an active breeding colony were verified through 2000. Roosting and foraging seems concentrated within extensive California fan palm groves throughout the upper Moapa Valley. Capture and acoustic sampling showed this to be the second-most abundant species in the valley. The diet included Coleoptera, Diptera, Hemiptera, Homoptera, Lepidoptera, and Orthoptera. This record represents the northernmost distribution of the species.

Infrared cameras and ultrasonic microphones were used to record big brown bats (Eptesicus fuscus) flying in natural conditions at night while they hunted for insects. As expected, bats avoided obstacles while flying through vegetation and intercepted flying prey in the open. But bats also appeared to capture insects near and possibly on the ground and near or in vegetation, flew low over water to drink, and pursued each other in aerial “dogfights.” In less than a minute, the same bat often used echolocation for several different tasks, showing a wider repertoire of sonar-guided behavior than revealed by previous observations limited to seeing bats flying against the evening sky or being photographed in fixed fields-of-view.

An ongoing study is being conducted to test the efficacy of the Anabat II detector and analysis system in obtaining reliable vocal signatures for the identification of non-phyllostomid species of bats. We sampled a wide range of elevations and associated habitat types throughout Belize. Anabat provides an instantaneous output of echolocation call structure with a laptop computer. Select sequences can be saved directly to the hard drive, avoiding extraneous noise and sound distortion commonly associated with tape recorders. To date, 18 of the 37 species known or expected to occur in the study region were identified by recognizable differences in the time-frequency characteristics of echolocation calls. In general, each family is recognizable by call structure patterns and species readily separated by frequency range parameters. Species that commute or forage at high altitudes are not susceptible to capture but are conspicuous by acoustic sampling. Further work is needed to determine limitations of the equipment, establish better sampling procedures, and develop a comprehensive library of vocal signatures incorporating the range of variation inherent in each species. As this work progresses, we predict the addition of hitherto unknown species occurring within the study region.

To evaluate the efficacy of the Anabat II ultrasonic detector and analysis system for use as a tool for conducting inventories, we compared results of acoustic versus capture techniques in the southwestern United States. We sampled 57 locations using standard methods (mist nets and double-frame harp traps) and simultaneously with an ultrasonic detector (Anabat II). Assuming total number of species obtained by both methods equaled a complete inventory, captures accounted for 63.5% and acoustic sampling 86.9% of the combined species present. Acoustic sampling was capable of sampling bats that routinely flew outside the sampling capabilities of nets and traps. We found no statistical difference between capture and acoustic sampling with respect to species that use low-intensity echolocation. Acoustic sampling of bat communities is a powerful tool but should be used with various capture techniques to perform the most accurate inventory.

A variety of ultrasonic (bat) detectors have been used over the past 3 decades to identify free-flying bats. Analyses of recorded echolocation calls were slow and typically restricted to few calls and at a resolution obscuring details of call structure. The Anabat II detector and associated zero-crossings analysis system allows an immediate examination, via a laptop computer, of the time-frequency structure of calls as they are detected. These calls can be stored on the hard drive for later examination, editing, and measurement. Many North American bats can be identified to species by qualitatively using certain structural characteristics of calls, primarily approximate maximum and minimum frequencies and morphological aspects of calls (e.g., linearity and changes in slope). To identify calls precisely, it is important to use a continuous sequence of calls from an individual in normal flight rather than from single isolated calls. All calls are not equally useful, and many fragmentary calls must be discarded before making a determination. Each sequence of calls must be examined to ensure that multiple bats have not been simultaneously recorded, which confounds correct identification. We found the percentage of non-usable calls within usable vocal sequences to be highest in vespertilionids (20–40%), whereas for other families this was frequently

Barclay (1999) criticized the qualitative approach for acoustic identification of species of bats (O'Farrell et al., 1999) on the basis of intraspecific variation due to geography, habitat, and species-assemblage factors. However, variations described to date represent minor variations in specific parameters of call structure and, with experience, present no difficulty in discriminating among species. Certain species, under certain circumstances, emit calls that may be confused with other species. These calls represent a small percentage of the total repertoire. Experience reveals these cases, and such calls should be judged unidentifiable. Barclay was concerned about a qualitative approach but stated that quantification has shown variation sufficient to negate the ability to identify species. The qualitative approach avoids this problem because it is not sensitive to minor quantitative differences.

In northwestern Belize, two emballonurids (Rhynchonycteris naso and Saccopteryx bili­ neata) and three monnoopids (Pteronotus pamellii. P. davyi, and P. personatus) were examined acoustically with the Anabat II bat detector and associated analysis system. R. naso used calls consisting of a short constant frequency (CF) at 47 kHz and concave downward frequency modulated (PM) sweep to ca. 40 kHz with two strong hannorucs. Echolocation sequences of S. bilineata revealed a paired cadence of calls. Both signals in a pair slowly increased in frequency, fonning a quasi-CF (QCF) component and tenninated with a short, downward PM sweep. The initial call of a pair ranged from 44.5 to 46.6 kHz and the second ranged from 46.6 to 48.7 kHz. P. parnellii used a long CF call at 63.5 kHz, with a tenninal downward PM sweep to ca. 54.5 kHz. P. davyi produced calls with an initial short CF at 68.1 kHz, a downward PM sweep, and a tenninal short CF at 58.0 kHz. P. personatus emitted calls similar in shape to P. davyi, with the initial CF at 83.0 kHz and the terminal CF at ca. 68.0 kHz. Previous descriptions of echolocation calls for these species compare favorably with those obtained in this study, but the Anabat equipment generally revealed more variation and detail than previously described. The echolocation calls described in this study provide precise vocal signatures for the accurate identification of free-flying individuals of the species studied. The recording and description of echo­ location calls of some Neotropical bats be­ gan with the pioneering work of Griffin (1953) and Griffin and Novick (1955). Al­ though data gathered were surprisingly good, technological limitations prevented recording under a variety of field condi­ tions. Thus, much of the early descriptions of vocalizations were generated from cap­ tive bats. Bats of the families Emballonur­ idae and Mormoopidae tended to produce high-intensity sounds that were easier to de­ tect and record than the low-intensity, high­ ly directional sounds produced by bats in the Phyllostomidae. Subsequent examina­ tion of some of these species. using im­ proved equipment, resulted in more defini­ tive descriptions of echolocation calls (Novick, 1963; Pye, 1973), although the

We evaluate several hypotheses concerning differential use of habitats by males and females based on data from live-trapping Peromyscus truei for 1 year. Multivariate statistical techniques revealed differential use of habitats by males and females during autumn and winter and different levels of habitat specificity throughout the year. Habitat use by males was less variable in autumn and winter, whereas habitat use of females was less variable in spring and summer. Niche breadth and overlap were density-dependent. Males shift use of habitat in response to reproductive condition of females, whereas females show little change in use of habitat throughout the year. Although the data do not falsify the eclectic-female hypothesis, they are most consistent with the reproductive-constraints hypothesis.

Two types of mesh live traps were better than Sherman traps for capturing rodents in high and low deserts, Mediterranean grassland and shrubland, and riparian woodland and scrub habitats ( P < 0.001). Mesh traps took more species and more individuals within a species than did Sherman traps, resulting in substantially different estimates of density, sex ratios, age structure, and movement. Kangaroo rats frequently kicked sand into Sherman traps, but not into mesh traps. A significant difference in trap response for a variety of rodents suggests a need for reevaluation of studies on populations, behavior, and distribution conducted with Sherman and other closed, box-type traps.

Echolocating bats (Pipistrellus, Myotis) sometimes fly in dense swarms for 1–2 h over desert water sources. Swarming is different from streaming at caves or roosts because ∼10–100 bats staying within a small volume (∼1000 m3) for an extended time rather than transiting. We study swarming using thermal infrared video cameras and a three‐microphone acoustic array. Swarming bats emit a steady stream of short (∼2 ms) FM sonar sounds with nearly identical sweeps and a collective duty‐cycle approaching 100%. Surprisingly, given the tendency to think in terms of bats in close proximity deliberately varying their signals for jamming avoidance, the signals of swarming bats are very similar. Video/acoustic tracks reveal no sign of mutual interference or collisions. It is not obvious whether bats gather to drink or to feed on insects, which also congregate near the water, or whether social behavior predominates. Some drinking occurs throughout the swarming period, but the occurrence of captures during swarming is ne...

A method for localizing sounds was applied to simultaneously reconstruct the emission pattern and flight path of echolocating bats. An infrared camera and an array of three microphones were used to record simultaneous audio signals and video images of groups of bats while foraging. The bats studied (Eptesicus, Myotis, Pipistrellus) use frequency sweeping ‘‘chirps’’ in the 25–45 kHz to 100–120 kHz band for echolocation. Cross correlation of the bats’ chirps was used to find delays in chirp arrival time between microphones in the array. These delays were then used to locate the chirps’ direction. A time‐series of these coordinates was found, then calibrated to pixel points of the corresponding infared video recording to reconstruct the flight path and chirp pattern for each of the bats over 15‐s intervals. By providing simultaneous emission and position information throughout time, this method addresses questions about dynamic adaptation of the emission patterns of bats to the acoustic environment. Simultaneous adaptation between bats flying in groups is particularly interesting. An accompanying abstract discusses the implications of these findings for the current paradigm of information processing in the FM bat’s auditory pathway.

Using an infrared body‐heat‐imaging video camera and a microphone array, we made field recordings of FM echolocating bats (Eptesicus, Myotis, Pipistrellus) while they deployed their sonar alone or in company with other bats. We observed cruising flights of bats in transit from roosts to feeding areas, bats flying low over water for drinking or hunting, and aerial interception maneuvers in open areas (larger insects were visible, too). However, we also recorded frequent captures of insects on or near the ground, flights into vegetation to capture beetles, and groups of bats flying in close proximity while drinking or making aerial captures of insects. Bat‐to‐bat dogfights were common, some involving two or more bats diving and violently maneuvering close to the ground or near vegetation. For single bats or several bats not very close to each other, we recorded typical interception maneuvers with pursuit sequences consisting of search‐, approach‐ (tracking‐), and terminal‐stage signals. By reconstruction of flight and emission patterns, we found that bats flying in close proximity alternated their broadcasts, and large aggregations of bats feeding close together perpetually emitted sounds characteristic of the mid‐approach stage, with short durations, high repetition rates, and no discernible terminal stages.

The properties of motor activity over a wide range of temperatures for 5 species of bats compared to a homeotherm and poikilotherm revealed the following: 1. 1. Force contraction of poikilotherms increase with a decrease in temperature. For homeotherms, force contraction remains relatively constant, losing contractability between 12° and 5°C. For bats, force contraction remains relatively constant over the entire test range of temperatures. 2. 2. Twitch duration increased for all species of animals tested, but for bats, the magnitude of duration was greater as temperatures were reduced. 3. 3. There was an inverse relationship between muscle size and force contraction for the bat species tested. 4. 4. The adaptive significance of motor activity at various temperatures is discussed with regard to known ecological behavior.

The echolocating bat,Plecotus phyllotis (Vespertilionidae), uses long-CF/FM and FM sonar sounds in different situations. The CF component in long-CF/FM sounds occurs at 27 kHz and has a duration of 20 to 200 ms. The FM component sweeps down from 24 to 12 kHz, with a prominent second harmonic from 40 to 22 kHz. This second harmonic sweep is interrupted at 28 to 25 kHz, providing a notch in the spectrum of the FM component at the CF frequency. This notch probably permits isolation of CF and FM components in echoes for separate processing, thus avoiding mutual interference with the different kinds of target information the two components convey. The FM component is also used without the CF component as a sonar sound. Two other FM orientation sounds are used when the bat is in a confined space such as a room. One contains only the second and fourth harmonics of the 24 to 12 kHz fundamental sweep, while the other contains only the fifth harmonic. This bat's repertoire of sonar sounds closely matches the hearing capacities of the genus.

1. 1. Nine of eleven species of desert bats tested demonstrated the ability to initiate and maintain flight at reduced body temperatures. This ability is associated with periodic activity throughout the winter. 2. 2. Of the two species studied most intensively, Pipistrellus hesperus demonstrated a stronger relationship between ambient and body temperatures than did Myotis californicus . It is hypothesized that differences in total body insulation are responsible for the difference in this relationship. 3. 3. Pipistrellus hesperus shows seasonal shifts in actual flight body temperature with a difference of 8–10°C between summer and winter. Spring and fall represent transition periods where the body temperature responds more directly to ambient temperature. Myotis californicus shows the same patterns only to a lesser extent. 4. 4. Low temperature flight appears to be an inherent physiological mechanism with no significant differences observed during laboratory experiments on a sexual or seasonal basis. 5. 5. Some variability is observed which appears to reflect the body condition and caloric and water balance. 6. 6. It is proposed that low temperature flight associated with winter activity is a mechanism adaptive for maintenance of water balance; but only incidentally of value as a feeding strategy.

An examination of the annual changes in brown fat deposits of Pipistrellus hesperus and Myotis californicus reveals: 1. 1. P. hesperus reaches peak brown fat levels in January and February, declining rapidly through March and April, then increases gradually through the remainder of the year. 2. 2. M. californicus , on the other hand, maintains peak levels of brown fat from December through February, decreasing gradually through August, then increasing rapidly in the fall. 3. 3.The major brown fat deposits for both species are interscapular, jugular, squamooccipitocervical and carotid bodies. 4. 4.The interscapular deposit (which accounts for 50–70% of all brown fat) appears to be a good index of brown fat dynamics. 5. 5.Brown fat appears to be important in maintaining body temperature during night at cold ambient temperatures.

Home range sizes were estimated seasonally for Microdipodops megacephalus and Perognathus longimembris and biweekly for Dipodomys merriami, D. ordii, D. panamintinus, D. microps , and Peromyscus maniculatus. Mean estimates are also presented for Reithrodontomys megalotis and Onychomys torridus . Principal component analysis was used to calculate home range values because of its ability to deal with a wide variety of home range configurations. All species showed great variability in home range size throughout the year. Shape of home range was similarly variable, although most species tended towards elliptical movement configurations. The heteromyids showed consistency in annual composite home range areas (0.33–0.49 ha) regardless of body size. The generally smaller cricetine rodents exhibited much larger composite home range areas (0.95–1.42 ha). Emphasis is placed on the utility of point-in-time estimates of movements rather than obtaining a single home range value, which subordinates the dynamic nature of small mammal movements.

1. 1. Oxygen consumption (OC), weight specific oxygen consumption (VO). heart rate (HR), breathing rate (RR) and evaporative water loss (EWL) differ in adult female Myotis thysanodes and M. lucifugus and are significantly related to thermoregulatory performance (regulating or conforming) and to reproductive condition but not to body composition, spleen or adrenal weights or age class. 2. 2. Multiple regression equation models of these physiological parameters as possible linear or exponential functions of ambient temperature (Ta), body temperature (T), T, to T differential, weight, and each other are presented. 3. 3. The relations of the physiological variables to Ta is curvilinear with OC, VO, RR and oxygen pulse (cm3 of oxygen consumed/heart beat) reaching minimal levels at similar optimal T's which exceed normally controlled T1. HR becomes minimal at T's approximating normally controlled Tl and EWL reaches minimal values at Ta's lower than controlled T1. Evaporative heat loss equals metabolic heat production at Ta's which exceed normally controlled T. 4. 4. Roosting energy budgets differ in the two species and are functions of reproductive status and thermoregulatory performance. The ability of regulating individuals to conform at low Ta's conserves a large portion of the roosting energy budget.

Density was estimated for the old-field mouse ( Peromyscus polionotus ) and the cotton rat ( Sigmodon hispidus ). Two types of trapping configurations, grid and parallel census lines, each with assessment lines, were used for density determinations. Live-trapping was followed by removal trapping on the same study sites. Population densities were calculated for each configuration from both sets of trapping data (live and removal). The results for both methods are compared and recommendations are given. Live-trapping using assessment lines appears to yield better estimates of density than removal trapping.

Twelve species of nocturnal rodents were studied on a 2.7-hectare plot of sagebrush desert in west-central Nevada. Six species, Dipodomys merriami, D. ordii, D. panamintinus, D. microps, Onychomys torridus, and Peromyscus maniculatus, were active throughout the year. Four species, Perognathus longimembris, P. formosus, Microdipodops megacephalus, and Reithrodontomys megalotis, hibernated and were active only in spring, summer, and autumn. Onychomys leucogaster and Neotoma lepida were trapped intermittently throughout the year but were not permanent residents of the area. Differences in time of daily activity were found between potential competitors demonstrating a degree of temporal isolation. Time after sunset and amount of moonlight were the two most important factors correlated to rodent activity. Ambient temperature, wind, cloud cover, precipitation, and water vapor pressure had little effect on activity except when extreme conditions prevailed. (auth)

Digestibility (82%) was measured directly for 10 cotton rats in the laboratory. Subsequently, digestibility was estimated using the ratio of ash in food and feces as well as the ratio technique with 15 specific elements. Digestibility estimates were all too low, therefore, the fecal ash values were corrected relative to a digestibility of 82%. Using the same correction factor with the modified ash ratio technique, digestibility was estimated to be 78% under field conditions. Digestibility values for the 23 field-caught cotton rats were all too low using the ratio technique for the 15 specific elements, however, the Ba estimate was 76%. Assimilation of each element under both laboratory and field conditions were estimated from digestibility values and the elemental concentration data for stomach contents and feces. Problems with estimating elemental assimilation are discussed relative to the specific elements examined.

An examination of warming rates of chest muscle in relation to rectal temperature and subsequent thermal mapping of selected tissues in active bats has shown the following trends: 1. 1. During arousal, chest muscle warms slightly faster than rectal temperature in Pipistrellus hesperus , Antrozous pallidus, Myotis californicus, M. thysanodes. Eptesicus fuscus , and Tadarida brasiliensis , whereas in Plecotus townsendii chest muscle warms twice as fast as rectal. 2. 2. Bats that warmed sufficiently to initiate flight in the laboratory had interscapular temperatures that were higher than rectal, brain, or adjacent flight muscles. 3. 3. Field data, however, indicate interscapular temperatures to be lower than flight muscle temperature, especially following periods of sustained flight. 4. 4. Both laboratory and field data show that certain bats are capable of coordinated and sustained flight at tissue temperatures well below recognized homeothermic levels.

1. 1. A zone of thermoneutrality exists for adult female Myotis thysanodes in early September in an ambient temperature range of 32·5–34·5°C with minimum metabolism of 1·74 cm3/g per hr. 2. 2. A transition from a homeothermic to a non-homeothermic metabolism to ambient temperature relation is evident by late September in adult female M. thysanodes. 3. 3. In early September, some adult female M. yumanensis exhibit a homeothermic metabolism to ambient temperature relation while others exhibit a non-homeothermic relation. 4. 4. In early September, adult M. lucifugus occultus of both sexes exhibit a non-homeothermic relation. 5. 5. At ambient temperatures above 32·5°C, metabolism in M. thysanodes increases at a significantly more rapid rate than in M. lucifugus occulttus. 6. 6. A critical thermal maximum ambient temperature of 44·5°C has been found for each of these three species.

1. 1. Mid-August to mid-September fat indices for female Myotis lucifugus were 0·58–0·69 g fat/g lean dry wt. with constant gross body composition. 2. 2. During the same trime span, fat indices of female M. yumanensis showed a gradual significant increase from 0·30 to 0·87 with a concurrent significant increase in percent non-fat and percent water. 3. 3. In mid-September, fat indices of M. thysanodes increased significantly from 0·09 to 0·73, while gross body composition was unchanged. 4. 4. M. thysanodes body fat had a caloric content of 9·418±0·016 kgal/g. 5. 5. Fatty acid analysis revealed 72–81 per cent unsaturation with oleic acid being the most abundant. 6. 6. For each species, females contained more body fat than males, and adults were fatter than young of the year.

Bats were netted at a desert spring in southern Nevada for a total of 70 nights covering each month of the year. Two species, Pipistrellus hesperus and Myotis californicus, were active throughout the year with peaks of seasonal activity during the warmer months. Antrozous pallidus was netted in all seasons of the year. Air temperature was a major factor affecting seasonal and nightly activity with more bats being netted at higher temperatures. However, both M. californicus and P. hesperus were active at air temperatures between −8° and 31 °C. During the warmer months, when air temperatures remained above 15°C for the entire night, both species sustained activity throughout much of the night, but in winter months, they were active only shortly after dusk and activity ceased when air temperatures dropped. Evidence for foraging and insect activity during the winter is presented. The hypothesis of continued year-round activity of bats in warmer areas of the southwest is presented as an alternative to hibernation or migration.

1. 1. Thermoregulatory patterns and levels of controlled body temperature (Tb) in adult female Myotis thysanodes and M. lucifugus throughout their stay in maternity colonies are significantly affected by stage of reproduction and even more by stage of pregnancy, but are not affected by abundance of body fat or age. 2. 2. It is impossible to distinguish regulating bats from conforming bats in ambient temperatures (Ta's) above 20–24°C, with bats of both species becoming partially hyperthermic above these Ta's. 3. 3. Minimum Tb required for initiation of flight averages 30·3 and 24·3°C, for M. lucifugus and M. thysanodes, respectively, while neonates of these two species begin to regulate at about 9 1 2 and 4 1 2 days after birth, respectively. 4. 4. Behavioral aspects of thermoregulation may be as important as physiological thermoregulation in the biology of these species.

Poddano analizie statystycznej zaleznośc miedzy wiekiem a ilością wody i bialka w organizmie nornic, Clethrionomys glareolus oraz ilorazem ilości bialka i wody. Zawartośc bialka i wody oznaczono u nornic pochodzących z dlugoletniej hodowli oraz u osobnikow stanowiących pierwsze pokolenie urodzone w hodowli z dzikich rodzicow odlowionych na początku i przed koncem sezonu rozrodczego.

Echolocating bats use different information-gathering strategies for hunting prey in open, uncluttered environments, in relatively open environments with some obstacles, and in densely cluttered environments. These situations differ in the extent to which individual targets such as flying insects can be detected as isolated objects or must be separated perceptually from backgrounds. Echolocating bats also differ in whether they use high-resolution, multidimensional images of targets or concentrate specifically on one particular target dimension, such as movement, to detect prey.

1. 1. Ten captive Myotis thysanodes ingested an average of 5·05 kcal/day and egested 0·47 kcal/day with a mean energy utilization of 90·8 per cent. 2. 2. One captive M. lucifugus ingested 4·15 kcal/day and egested 0·37 kcal/day with an energy utilization of 91·2 per cent. 3. 3. M. thysanodes gained an average of 2·77 cm 3 /day of water and lost an average of 2·86 cm 3 /day. This represents a water turnover of almost half the total body water. 4. 4. The M. lucifugus gained 1·97 cm 3 /day of water and lost at least 1·47 cm 3 /day representing a water turnover of about one third of the total body water. 5. 5. It is suggested that for small mammals in general that the energy utilization approaches or exceeds 90 per cent efficiency.

The small mammal communities in four major plant associations were examined in the Whirlwind Valley, Eureka and Lander Counties, Nevada. All associations have been extensively grazed by livestock. Live trapping plots were placed and sampled seasonally in each habitat. Dipodomys microps and Perognathus parvus were the primary species within the big sagebrush and shadscale associations. In the greasewood association, P. maniculatus and Eutamias minimus were primary species. Microtus montanus, Reithrodontomys megalotis, Sorex vagrans, and Thomomys talpoides formed the small mammal community in the marsh-meadow association. Density was low on all plots, not exceeding a total of 13 individuals/ha. Grazing pressure probably accounts for the low habitat quality which did not support more than 0.6 kg/ ha biomass in shadscale and big sagebrush-shadscale, whereas less than 0.3 kg/ha was supported on each of the remaining habitats. Mammal species diversity was highest in greasewood and the ecotonal plot which corresponded to the habitats with the greatest plant diversity, cover, and vertical structure. The composition of small mammal communities changes from east to west in the Great Basin Desert of Nevada (Hall, 1946). The western edge of Nevada contains components of the southern Nevada Mohave Desert fauna that is lacking in the remainder of the northern part of the state. Detailed population studies which relate the temporal and spatial properties of small mammal community structure have not been conducted in northeastern Nevada. The high elevation, cold Great Basin Desert encompasses the intermontane region of Nevada, California, Utah, Idaho, Oregon, Washington, Montana, and Wyoming. In addition to the expected rigors of desert existence, small mammals must also cope with winters marked by intense cold. Inasmuch as this desert region consists of such a massive area, there are considerable variations in habitat mosaic and concomitant structural differences within respective small mammal communities. The shrub-steppe of south central Washington represents a six-species system of small mammals with 99% of the community represented by Perognathus parvus and Peromyscus maniculatus (O'Farrell et al., 1975). The Great Basin scrub of eastern California had a seven-species system with virtually all of the individuals belonging to Dipodomys microps, D. merriami, and Perognathus longimembris (Kenagy, 1973). Several habitat types were examined in Idaho and the composite community consisted of five species (Larrison and Johnson, 1973). A total of 12 species was documented for a sagebrush community in west-central Nevada (O'Farrell, 1974). Measures of seasonal population fluctuations are presented for all of these studies. The purpose of this study was to provide a baseline description of existing faunal conditions in the Whirlwind Valley in northern Nevada as a part of an environmental assessment of the Geysers Geothermal Resource Area. A thorough seasonal examination took place in all the major habitat types within this valley. T E S TH ESTERN NATURALIST 31(1):23-32 MARCH 31, 1986 This content downloaded from 157.55.39.192 on Wed, 24 Aug 2016 05:56:20 UTC All use subject to http://about.jstor.org/terms The Southwestern Naturalist STUDY AREA-The Whirlwind Valley is located about 80 km west of Elko, in portions of Lander and Eureka Counties, Nevada. The valley is formed by a bifurcation of the northern end of the Shoshone Range, bordered on the northwest by the Argenta Rim and on the southeast by the Malpais. Plant associations were mapped using aerial photographs and extensive ground truthing and designated by the nomenclature of Cronquist et al. (1972). Species identification follows Cronquist et al. (1972, 1977) and Holmgren (1942). Four major plant associations were found: big sagebrush, shadscale, greasewood, and marsh-meadow. The big sagebrush association occupied the upper elevations (1525 to 2205 m), including the Malpais with its steep northern slope. Soil tended to be rocky (17% ground cover). Dominant perennial species consisted of Artemisia tridentata, Poa nevadensis, Gutierrezia sarothrae, Grayia spinosa and Sitanion hystrix, in decreasing order of importance. Abundant annuals were Microsteris gracilis (30.2/m2) and Bromus tectorum (3.5/m2). Aerial perennial cover was 29% and mean height was 25.2 cm + 5.0 (1 S.E.). Perennial species richness was 18, diversity (H') 1.82, and evenness (V') 0.63. The shadscale association occurred adjacent to and interdigitated with big sagebrush (1463 to 1525 m) throughout most of the valley floor and gentler slopes. Soil tended to be less rocky (10% ground cover) and more saline than at the higher elevations. Dominant perennials were Atriplex confertifolia, Artemisia spinescens, Grayia spinosa, and Poa nevadensis. Annuals were dominated by Lepidium perfoliatum (49.2/m2), Microsteris gracilis (23.0/m2), and Bromus tectorum (14.9/ m2). Aerial perennial cover was 24% and mean height was 21.1 cm ± 6.2. Perennial species richness was 9, diversity 1.48, and evenness 0.67. The greasewood association occupied the lowest elevations (1402 to 1463 m) and the most saline soils. The soil surface predominantly was a salty crust devoid of rock. Dominant perennials were Sarcobatus vermiculatus, Suaeda fruticosa, Distichlis stricta, Chrysothamnus parryi, and Atriplex lentiformis. The primary annual was Atriplex pusilla (8.4/m2). Aerial perennial cover was 45% and mean height was 41.9 cm ± 12.7. Perennial species richness was 10, diversity 1.70, and evenness 0.74. The marsh-meadow association was a relatively small, discrete patch found in the runoff areas from the geothermal pools. This area was limited to seepage zones where water was readily available (1402 to 1463 m). Predominant perennial species were Distichlis stricta, Juncus balticus, Carex spp., Scirpus nevadensis, and Solidago spectabilis. Vegetative cover, excluding litter, was 70%. Climatic records taken during this study show some differences when compared to long term trends (Table 1). Mean temperature extremes differed slightly for most months although mean minimum values were generally higher than long term values from August 1982 through January 1983. Rainfall in 1982 was 5.3 cm greater than the 11 year mean. Large quantities of rain in March and September coupled with warm temperatures provided suitable conditions for germination and growth of annual vegetation. Data on livestock use in the Whirlwind Valley is generic at best. Bureau of Land Management (BLM) data is given in animal unit months (AUM); one animal unit (1 cow, 455 kg, plus a calf