W. Glen Bradley

Activity Patterns of Bats over a Desert Spring

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.

Reproduction and Food Habits of Merriam's Kangaroo Rat, Dipodomys merriami

Collections of Merriams kangaroo rat ( Dipodomys merriami ) were made from a creosote bush community near Las Vegas, Nevada, during the period 30 May 1962 to 31 January 1965. All months of the year were represented and 985 specimens were examined. The reproductive condition of all specimens was determined. Some males were in reproductive condition, as evidenced by scrotal testes or abdominal testes 5 millimeters long or longer, during all months of the year. Approximately 50 per cent or more males were in reproductive condition during the period February through September. Some females were reproductively active in the period January through August. Visible embryos, recent placental scars, lactation, and swollen vulva were the criteria for determining reproductively active females. Two or more litters may not be uncommon. The stomachs of 740 kangaroo rats were examined and food items were separated into categories of seeds, greens, and insects. The diet is primarily made up of seeds. Greens were an important source of food in the period February through May and again in August. Greens made up more than 30 percent by volume of the stomach contents during these months. We suggest that greens are utilized primarily as a source of water during the period of reproduction.

FALL AND WINTER BAT ACTIVITY AT A DESERT SPRING IN SOUTHERN NEVADA

Bats were captured in a mist net at White Spot Spring, Desert Game Range, Clark County, Nevada during the months September through May for a total of 21 mist net nights. Time of capture, air temperature, and wind conditions are given for each species. Two species, Pipistrellus hesperus and Myotis californicus were active throughout the fall and winter. Pipistrellus was netted at air tempera- tures ranging from 10 to 310 C. Myotis californicus was netted at air temperatures of 20 to 270 C. Approximately 48% of the Myotis were taken at air temperatures be- tween 2o and 60 C. and approximately 11% of the Pipistrellus were netted at air temperatures of 50 C. or below. A third species Antrozous pallidus was netted in low numbers at air temperatures as low as 20 C. Studies of bat activity have usually been conducted during the spring, summer, and early fall months when bat activity is highest. Since bat activity is low or non-existent in temperate areas during the fall and winter, few data on activity are available for these seasons. The present study provides some indications of fall and winter activity for certain species found to be active at these seasons in southern Nevada. DESCRIPTION OF THE STUDY AREA. White Spot Spring is lo- cated at 4460 feet elevation, on the north-facing slope of the Las Vegas Range, Desert Game Range, Clark County, Nevada. The spring flow is contained within a stone tank which is approximately 11.5 feet square by 2 feet deep. The tank was usually full of water. It is bordered on one side by Tamarix spp. and Phragmites communis. The surrounding area consisting or rolling hills is covered by various desert shrubs in- cluding Coleogyne ramosissima, Larrea divaricata, Yucca schidigera, and Atriplex canescens.

HOME RANGE, ACTIVITY PATTERNS, AND ECOLOGY OF THE ANTELOPE GROUND SQUIRREL IN SOUTHERN NEVADA'

Live trapping data from the Desert Game Range in southern Ne- vada were used to determine the activity patterns and home range of the antelope ground squirrel, Citellus leucurus. Young ground squirrels appear above ground in the late summer. Few animals remained on the study area by the following spring. Above-ground activity occurs at that time of the day when temperatures are mod- erate. Live trapping data as indicated by the number of daily captures and average range of daily movements clearly suggest that temperature is a major factor in- fluencing activity. Squirrels are largely inactive at temperatures below 10? C. and above 320 C. and are most active in September, a time when moderate temperatures occur throughout the day. The winter and early summer are periods of reduced activity as revealed by fewer captures and shorter average range of movements for daily and monthly periods. Home ranges by the greatest distance between captures method averaged 20.6 acres as contrasted with an estimate of 14.9 acres by the mini- mum home range plus estimate method and eight acres by the distance between random points of capture method. Data from nine squirrels captured 20 or more times, strongly indicate that ap- proximately 20 captures are needed for a reliable estimation of home range. In ad- dition captures should occur over a period of at least one month for a good estimate of home range in this species. Average daily range of movements indicate that this ground squirrel utilizes an area of approximately four acres for periods of one or more days. Over a period of time a ground squirrel moves throughout all of the segments of a home range. The area of daily activity may be called a daily range in contrast to the home range which contains several daily ranges. The large home range consisting of several smaller daily ranges enables ground squirrels to utilize a large area in search of a wide variety of seasonal food items. During periods of un- favorable weather, short excursions can be made from numerous burrows found within the daily ranges thereby avoiding the extremes of the desert environment.

COMPARATIVE THERMAL RELATIONSHIPS OF FLIGHT FOR SOME BATS IN THE SOUTHWESTERN UNITED STATES

Abstract 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.

Ecological Distribution of Fishes of Moapa (Muddy) River in Clark County, Nevada

Abstract Fish collections were made at nine stations along the Moapa River of southern Nevada. Four native species are ecologically separated into headwater and middle-stream types. The headwater fishes are ecologically segregated into one pond species (Crenichthys baileyi) and one stream species (Moapa coriacea). The apparent temperature preference for both species is near 29.5 C. Temperature range for Crenichthys is 27–32 C and for Moapa 19.5–32 C. Both Gila robusta and Rhinichthys osculus are most abundant in the turbid middle portion of the stream in undisturbed, deep riffle habitats. A fifth native species, Plagopterus argentissimus, is extremely rare or of accidental occurrence. The unsaturated Moapa River environment has been easily colonized by exotic or non-native species, most recently and most successfully by Poecilia mexicana. An additional species, Gambusia affinis, is widespread and abundant throughout much of the stream. Cyprinus carpio, Notropis lutrensis, Pimephales promelas, Ictalurus me...

Night Roosting Behavior in Four Species of Desert Bats

Various aspects of night roosting behavior were observed for four species of desert bats. Variability in night roost utilization was found for those species for which adequate observations were available. Myotis californicus roosted primarily in desert shrubs or trees, depending on availability. Pipistrellus hesperus utilized rock, rock crevices, and desert shrubs as primary roosting sites, rock being preferred when in close proximity to water. Antrozous pallidus was more flexible in roosting behavior, utilizing small trees, rock crevices, and an abandoned shed. In contrast, Tadarida brasiliensis roosted in a bridge expansionjoint where they were also found during daylight hours. Night roosting for digestion and subsequent weight loss reduces wing loading, thereby allowing considerable energy conservation in further foraging activity or long flights back to day roosts. During daylight hours, bats seek shelter in a wide variety of habitats. Day roosts have been described in numerous previous studies. Existing data on night roosts, however, are limited and have resulted mainly from accidental encounters in buildings, bridges, mines, caves, and rock crevices (Barbour and Davis 1969). In desert areas bat activity is concentrated near free water, which may be located at a considerable distance from roosting sites. There are, however, numerous isolated mountain ranges and adequate vegetation which could provide suitable night shelter. Where typical roosting sites occur adjacent to a water source, night roosts for some species of desert bats have been described (Dalquest 1953; Krutzsch 1954; Orr 1954; Cross 1965; Barbour and Davis 1969; Poche and Ruffner 1975). In this study we attempted to locate and describe night roosts in areas of the Mojave Desert where night roosts have not previously been identified. MATERIALS AND METHODS. Bats used for roosting behavior observations were collected at various locations in southern Nevada and northern Arizona (600-1480 m elevation) during the period July-September 1975. Roosting behavior observations were made on 34 Myotis californicus, 32 Pipistrellus hesperus, 26 Antrozous pallidus, and 24 Tadarida brasiliensis.

The Vegetation of Saratoga Springs, Death Valley National Monument, California

The vegetation of Saratoga Springs and adjacent areas was sampled by means of 1 meter2 quadrats placed at 4 meter intervals along randomly located transects. The frequency of occurrence, average percent cover and numbers of perennial species was computed for each community belonging to xerophytic shrub, phreatophytic shrub and marsh vegetation types. Plant communities arranged along moisture and salinity gradients clearly indicate the importance of water availability and salt content of the soil. Xerophytic and phreatophytic shrub communities have fewer perennial species, lower percent cover and a lower standing crop than plant communities within the marsh. In general, plant communities form a vegetation mosaic in the marsh and vegetation belts or zones along sharp environmental gradients (salt concentration and water availability) adjacent to the marsh. Chapman (1960) reviewed the salt marsh vegetation of the world, including inland salt marshes. Jenson (1963) reported on the edaphic and- aquatic plant relationships in marshes bordering Great Salt Lake, and Bolen (1964) studied a spring fed salt marsh in western Utah. There are no studies of salt marsh vegetation in Death Valley and few detailed studies of the vegetation of the Death Valley region. Coville (1893) in his report on the sytematic botany of the Death Valley region included much of interest to the plant ecologist. Went (1949) and Went and Westergard (1949) have studied the effects of temperature and precipitation upon the germination of desert plants, especially annuals. Hunt (1966) has recently studied the distribution of the major perennial plants in Death Valley in relation to soils and geology. The perennial vegetation of Saratoga Springs and the surrounding desert habitats are covered in this report. STUDY AREA. Saratoga Springs lie in the extreme southern portion of Death Valley National Monument at an elevation of 195 ft. in the NW1/? Sec. 2, T. 18N., R. 5 E. One main spring source occurs at the southern tip of the base of a ridge that extends southward from the Ibex Mountains. Three addi- 111

POPULATIONS OF TWO SONORAN DESERT PLANTS, AND DEDUCTIONS AS TO FACTORS LIMITING THEIR NORTHWARD EXTENSION

Recently discovered populations of ocotillo Fouquieria splendens, and smoke tree, Dalea spinosa in extreme southern Nevada were studied. Sparse distribution, reduced vigor and size all indicate that these populations have reached their northern geographic and ecologic limits. It is suggested that nothern dispersal and establishment of smoke tree is checked in extreme southern Nevada by lowered and more prolonged winter temperatures. Populations of ocotillo are disjunct and may be relict. Populations of ocotillo, Fouquieria splendens, Engelm and smoke tree, Dalea spinosa Gray have recently been located along the Colo- rado River in extreme southern Nevada. Neither species has been defi- nitely reported prior to this study as occurring in Nevada although Tidestrom (1925) and Muller (1940) suggest the possibility of oco- tillos being present in the most southern part of the state. Both species are found in the southern part of the Mohave Desert and are wide- spread in the more southern Sonoran Desert. The most northern ex- tension of the Sonoran Desert in California is in the vicinity of Needles, California where both species are found in suitable habitats. The population in Nevada represent a northern extension of the known range of both species into the northern Mohave Desert. No- menclature used in this paper follows Munz (1959). DESCRIPTION OF THE STUDY AREA. The area studied was the flood plain of the Colorado River on the Nevada side extending from south of Davis Dam to the California-Nevada boundary. The flood plain along this portion of the river is several miles wide, usually about three miles in width on the Nevada side, and varies from about 700 to 500 feet in elevation. The soil is primarily alluvial sand but small areas elevated above the main flood plain may be sandy loam. Several vegetation types are represented, the most common and widespread being creosote bush (Larrea divaricata) and burro-weed (Franseria dumosa). Thick stands of quail bush (Atriplex lenti- formis) are located near the river. Riparian populations of such species

Growth and development of two species of chipmunks: Eutamias panamintinus and E. palmeri.

Growth rates and developmental patterns were determined on four litters each for two species of chipmunks, Eutamias panamintinus and E. palmeri , raised in the laboratory. E. palmeri were larger and had a faster rate of development in the early postnatal period, that is, earlier appearance of hair on head, erect pinnae, ability to stand, eruption of upper incisors, and appearance of cheek teeth. In weight and linear measurements, E. palmeri had faster growth rates than E. panamintinus . Constant growth rate (k) based on weight for E. panamintinus was 0.076 and for E. palmeri , 0.092. An accelerated ontogeny is characteristic of sciurids that hibernate; therefore, we attribute the more rapid growth rate of E. palmeri to its more extended period of hibernation at higher elevations.