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Bat Monitoring Study

In Clark County, lowland riparian habitats are found along the Virgin and Muddy Rivers, Las Vegas Wash (Wash) and the Colorado River. These riparian ecosystems provide essential habitat for a variety of bat species in this arid desert environment. A two-year monitoring study, completed in January 2006, filled the void of information regarding these nocturnal creatures and their use of the Wash and expanded the body of knowledge regarding bats in Southern Nevada, of which not much had previously been known. Prior studies, conducted more than a decade ago, involved collections at discrete fixed points using standard capture methods and rarely entailed repeated temporal sampling. Capture results were biased due to the small surface area of sampling devices and the necessity of placing these over water, in fly-ways or in other specialized situations where concentrations of bats can be expected. Results were further biased by the fact that foraging bats detect and avoid traditional capture devices.

batThe purpose of this study was to investigate bat species diversity and activity along the Wash by utilizing acoustic monitoring systems. Since bats use echolocation calls (high-pitched ultrasonic sounds made by their vocal chords) to “see” with their ears, we were able to record these calls and later use them to identify the species of bat that made them. This study resulted in the collection of baseline information for the bat community in the Wash. This data will help with the long-term management and conservation of identified species.

Recent advances in acoustic technology have resulted in a passive monitoring technique that can be used to study bat activity and community diversity. Acoustic sampling has been shown to be superior to standard capture methods for inventory and activity studies. As with capture methods, the area sampled acoustically is finite and species-dependent (e.g., loud species will be detected at greater distances than quiet species) and thus passive monitoring techniques are not without inherent bias, but sampling volume is far greater than with nets or traps. Unlike capture methods, acoustic sampling is not restricted to fixed-points but can be used in mobile surveys allowing for a landscape-scale examination of bat distribution and habitat use. With the appropriate acoustic equipment (e.g., Anabat II) and adequate experience, echolocation calls can be used to identify species presence.

Three acoustic monitoring stations collected nightly data along the Wash. These stations consisted of an Anabat II bat detector fitted with a Hi-Mic microphone, a Compact Flash Storage Zero-Crossings Interface Module (CF ZCAIM), and a data logger configured to record temperature and light intensity. The stations were mounted on a metal pole and secured to the ground with a concrete footing.

Echolocation calls were detected by the Anabat II and stored as digital files to the Compact Flash memory card. The files were later downloaded to a computer and viewed through the Analook software. The files were interpreted by Dr. Michael O'Farrell (www.mammalogist.org), a pioneer and expert in the field of bat biology. This technology also allowed the distinction among various behavioral activities, such as foraging, drinking, or simply commuting activities. Species richness (diversity) was generated for each sampling period.

Data collected from the acoustic monitoring stations revealed the presence of 17 species using the Wash. They are the California myotis (Myotis californicus), western yellow bat (Lasiurus xanthinus), Brazilian free-tailed bat (Tadarida brasiliensis), pallid bat (Antrozous pallidus), Yuma myotis (Myotis yumanensis), hoary bat (Lasiurus cinereus), western pipistrelle bat (Pipistrellus hesperus), big brown bat (Eptesicus fuscus), Townsend's big-eared bat (Corynorhinus townsendii), western red bat (Lasiurus blossevillii), western small-footed bat (Myotis ciliolabrum), greater mastiff bat (Eumops perotis), Allen’s big-eared bat (Idionycteris phyllotis), California leaf-nosed bat (Macrotus californicus), big free-tailed bat (Nyctinomops macrotus), fringed myotis (Myotis thysanodes), and silver-haired bat (Lasionycteris noctivagans).

Many of the species identified during the study are on sensitive species lists maintained by both federal and state agencies. In addition, six of the species detected had never been recorded in the Las Vegas Valley before. These species include: M. ciliolabrum, M. thysanodes, M. yumanensis, L. blossevillii, L. xanthinus, and I. phyllotis.

Data from the study was presented at the North American Symposium on Bat Research (NASBR). NASBR is a "society dedicated to the promotion and development of the scientific study of bats." The meeting, held in October 2005, was the annual meeting of bat researchers from North America where all scientific aspects of bats, including conservation and public education, are discussed.

Long-term monitoring of bat populations associated with extensive riparian restoration in Las Vegas Wash, Clark County, Nevada
Long-term monitoring of bat populations associared with extensive riparian restoration in Las Vegas Wash (PDF)

For more information on the individual bats found in Nevada, you can visit the Nevada Bat Working Group website. This website lists all of the bats found in Nevada. The site includes scientific and common names, distribution, habitat characteristics, resident status, winter status, roost sites, reproduction, food habitat, status of protection and conservation/management issues.

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Las Vegas Wash Project Coordination Team • 100 City Parkway, Suite 700 • Las Vegas, NV 89106 • (702) 822-3300