Michael J. O'Farrell

Qualitative Identification of Free-Flying Bats Using the Anabat Detector

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 <10%. Active rather than passive collection of data maximizes quality and quantity of diagnostic calls and provides a contextual base for the investigator.

A Comparison of Acoustic Versus Capture Techniques for the Inventory of Bats

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.

Use of a Mesh Live Trap for Small Mammals: Are Results from Sherman Live Traps Deceptive?

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.

HABITAT USE BY BATS IN A RIPARIAN CORRIDOR OF THE MOJAVE DESERT IN SOUTHERN NEVADA

Abstract 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.

Spatial Relationships of Rodents in a Sagebrush Community

Twelve species of nocturnal rodents were studied on a 2.7-ha plot of sagebrush desert in westcentral Nevada. Species richness appeared to be augmented by food resource allocation, microhabitat selection, temporal partitioning, and the establishment of an interspecific dominance hierarchy. Three species ( Dipodomys mi-crops, Perognathus formosus , and Neotoma lepida ) were restricted to the shadscale habitat. One species, D. ordii was restricted to sand dunes, and one species, D. panamintinus , was restricted to big sage habitat. Three species, D. merriami, P. longimembris , and Peromyscus maniculatus , appear to be habitat generalists. Intraspecific overlap values indicate that D. merriami and P. longimembris are the most social of the heteromyids studied, although Peromyscus maniculatus was the only species exhibiting intraspecific overlap throughout the year. Between-sex overlap was greatest during reproduction. Male-male overlap was most prevalent for all species except P. longimembris , which exhibited greater female-female overlap. The magnitude of total overlap tolerated by a species showed a positive density relationship although on an individual basis, overlap values tended to remain fairly constant. Interspecific overlap was low except for the habitat generalists, which tended to use more habitat patches. By using principal component analysis to study changes in home range shape, size, and orientation, one can assess changes in overlap and space utilization. This technique should enhance our knowledge of small mammal social structure.

Home Range Dynamics of Rodents in a Sagebrush Community

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.