Acoustic methods for sampling chiropteran diversity at the Sevilleta National Wildlife Refuge
Ariana Ananda, John Muir College, University of California San Diego, La Jolla, CA 92092
William Gannon, University of New Mexico, Albuquerque, NM 87131 Bats are incredibly important to the environment, serving as seed dispersers, pest controllers, and have a large potential to be bio-indicators of overall environmental health (Jones, et. al. 2009). Because of this, it is essential to monitor their trends in abundance and diversity to assess environmental health, especially at Long-term ecological research sites such as the Sevilleta National Wildlife Refuge (SNWR). In order to assess chiropteran diversity across different habitats at the Sevilleta NWR we planned to collect ultrasonic echolocation signatures of bats from various habitats and analyze with the Anabat™ ultrasonic detector (Titley Electronics, Ballina, New South Wales, Australia) and Analook analysis software. A self-contained detector system was to be deployed at sites chosen for habitat and management qualities. Detectors were to run for 8-10 days at each, after which call files would be downloaded. All calls would then be reviewed and verified by experts to confirm the bat species present. Data from a study 15 years ago was to be used as a comparison baseline for present diversity levels. The purpose of this study was to explore conservation applications based on the success of drinkers attracting a wide diversity of bats. Due to the technological difficulties that come with the steep learning curve required to utilize these devices, only one site was successfully monitored, and only for three consecutive nights. However, data from those three nights showed a considerable amount of diversity for a single location—10 different species were detected. When compared to a study conducted at the Sevilleta NWR in 1999, a total of 7 species were captured between four different sites.
Surveying bat diversity is an important way to examine environmental health. Bats play a large ecological role and maintain important relationships with both plants and other organisms. Bats are valuable bioindicators based on their taxonomic stability, the measurability of short and long-term effects on populations, and their sensitivity to environmental stressors such as drought, climate change, water quality, and pesticide use (Jones, et. al. 2009). Bats also provide several ecosystem services. Like all animals that aid in the process of seed dispersal, bats play an important role in plant success when they consume seed-bearing fruits by decreasing competition among seedlings as they move seeds farther from the parent plant, and allow plants to colonize new habitats as the animals that carry their seeds travel to new areas (Howe and Smallwood 1982). In the desert, bats serve as key pollinators for many species of cacti and agave (Allen-Wardell, 1998). With their highly mobile lifestyle, bats are incredibly effective long-distance dispersers of seeds and pollen and are critical in plant habitat regeneration (Muscarella and Fleming 2007). Bats also serve as important insect regulators, with a single bat consuming 4-8g of insects each night—most of these pest species. (Boyles 2011). The economic role bats play is so large that in Texas, for example, bat’s value as pest control for cotton farms shows an annual value of over $700,000 (Cleveland, et. al. 2006).
The Sevilleta NWR, located 20 miles North of Socorro, New Mexico encompasses four different biomes in its nearly 230,000 acres, including the Colorado Plateau Shrub Steppe, Great Plains Short Grass Prairie, the Chihuahuan Desert, and the Pinyon-Juniper Woodland. This could potentially provide important habitat to many of the ~27 bat species found in New Mexico. Habitat selection by bats is thought to be driven by a combination of foraging and roosting requirements (Findley, 1993) and choice of foraging habitat by bats may depend upon their wing design and the frequency of their echolocation. While some species are more specialized to forage in cluttered habitats, others are more equipped to forage in open environments solely based on the morphology of their wings and calls (Aldridge and Ratenbach, 1987; Gannon, unpublished data). With this project we wanted to utilize acoustic ultrasonic technology to assess species diversity at the Sevilleta NWR to understand what species are using the various habitat sources present and wanted to predict where species could be documented based on existing records as well as bat morphology.
Acoustic monitoring was chosen as a main avenue for studying bats at the Sevilleta due to its efficacy for conducting inventories of species. Unlike tradition mist-netting for bat identification, acoustic monitoring allows researchers a wider scope for sampling bats. Ultrasonic detectors are capable of sampling bats that routinely fly outside of the capabilities of nets and traps (O’Farrell and Gannon 1999), are mobile, and allows for passive sampling. Two models of the Anabat detectors were used, the Anabat SD2, and the older Anabat II. The ultrasonic Anabat SD II detector can be deployed in the field and record calls for multiple nights off battery reserves, requiring no researcher to be present for the entire duration. The SD2 can also provide real-time feedback in the field. If a laptop or PDA is connected to the recording device, immediate examination of echolocation calls is possible. The calls can be stored on a hard drive if recorded directly from a laptop (Anabat II) or can be stored on a CF card which is inserted into the device (Anabat SD2). The files can later be analyzed using Analook software to visualize the calls. Many bats can be identified to the species level by analyzing structural characteristics of calls, maximum and minimum frequencies, and linearity and changes of slope (O’Farrell, Miller, and Gannon 1999). Although acoustic monitoring provides an efficient way to evaluate bat diversity, it should always be used in conjunction with capture techniques to achieve the most accurate record of species (O’Farrell and Gannon, 1999).
Targeting vital resource areas for bats at the Sevilleta NWR, areas near water were chosen as monitoring sites. These included Nunn Well, a man-made drinker on open Chihuahuan grassland, Cibola Springs, a natural seep near the base of Los Pinos Mountains, and the Sevilleta Mesa trail, a gateway to a manmade pond. Two mobile Anabat units were planned to be deployed concurrently at two different sites. After a period of 1.5-2 weeks, the mobile units would be moved to the remaining site. We expected the cohorts of species to be ecomorphologically different as high, fast flying species (such as Tadarida brasiliensis) would likely be detected at Nunn Flats, whereas species more adapted for flying in clutter or short-distances (e.g., Parastrellus, Myotis) would likely be present at the natural Cibola Spring. Species that are open-foragers yet are not especially fast flying may occur at all sites in equal numbers (e.g., Antrozous pallidus).
Of these three sites, the only one assessed this season was the area surrounding the man-made pond outside the Sevilleta Field Station. The Anabat SD2 mobile unit was deployed on the Mesa trail for two weeks on-and-off, but each collection provided no successful recordings and only delivered error messages. Technical difficulties deploying the Anabat SD2 device in the field forced us to utilize a less mobile method of acoustic recording. Instead, the older Anabat II device was used. The Anabat II device consists of a broadband bat detector with a condenser microphone that can be processed and transferred by the Anabat Zero-Crossing Analysis Interface Module (ZCAIM) to a computer running a DOS operating system (Fenton, Bouchard, Vonhof, and Zigouris, 2001). Unlike viewing calls in Analook, the DOS operated Anabat II allows the researcher to playback bat calls and actually hear them, while also seeing a display of the echolocation graph. However, the Anabat II must remain connected to the computer and cannot be left out in the field unattended. To combat this, we set up the Anabat II on a tri-pod and deployed it out the back door of a field station house located near the Sevilleta pond. The DOS computer was mounted on the washing machine and the extension cord was fed through the door allowing the computer to remain safe from the elements while the Anabat II recorded data outside. This method was used for three nights, July 25th, 26th, and 27th. A second Anabat II and DOS computer combination existed, but attempts to set it up and record data were unsuccessful.
From these three nights of recording by the pond, 10 different species were identified by their acoustic signature (Table 1). This shows the potential for a higher amount of diversity than previously known throughout the Sevilleta NWR, as the other proposed habitat sites may hold even more species. A capture survey conducted in 1992 at the Sevilleta NWR found a total of 7 species across four different sites sampled over three months (Table 2, Gannon 1992). From the two surveys, a combined 14 different species are shown to be present at the Sevilleta NWR. It should be noted that the 1992 studies were not acoustic surveys and that capture techniques can have low success rates and actual diversity may have been higher.
These surveys are important because if conducted regularly, they can provide us with data to measure the short and long-term effects on bat populations that are occurring from both natural procedures (such as drought and El Niño events) and anthropogenic causes (pesticide use, water quality, habitat destruction). It is important to know which habitats are being utilized by bats within the Sevilleta NWR so that they may be monitored for quality and conservation. In the future we hope a more permanent monitoring system can be implemented that can be accessed remotely through Sevilleta WIFI for future research. A solar-powered Anabat system that would record calls nightly would allow for long term research of diversity and abundance to be conducted by researchers from their home institutions. Having this call data be available to the public public could open doors for countless scientific projects in the future.
Table 1: Chiropteran species identified by their acoustic signature based on three nights of monitoring with the Anabat II device positioned near Sevilleta Field Station pond. 10 different species were identified.
Table 2: Data of chiropteran species captured using mist nets in a survey conducted in 1992. Seven species were captured at a total of four different sites.
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