I Radiotelemetry Techniques and Analysis SYBILL K. AMELON DAVID C. DALTON JOSHUA J. MILLSPAUGH SANDY A. WOLF -0 ADIOTELEMETRY HAS BECOME AN IMPORTANT tool in studies of animal behavior, ecology, management, and conservation. R From the first decades following the introduction of radio transmitters, radiotelemetry emerged as a prominent and critically important tool in wildlife science for the study of physiology, animal movements (migration, dispersal, and home range), survival, animal abundance, and resource selection. Advancements in technology since 1988 include subminiaturized transmitters, improved receiv- ing systems, satellite receivers, and global positioning systems (GPS), as well as increased computer hardware and software capabilities to process data collected in radiotelemetry studies. These advancements have revolutionized radiotelemetry studies and made it possible to use this tool for increasingly smaller species. The use of radiotelemetry requires an understanding of the techniques, limita- tions, and appropriate applications of this tool. Kenward (1987, 2001), White and Garrott (1990), Millspaugh and Marzluff (2001), and Fuller et al. (2005) provide re- views and detailed information on the technology, study design, and analysis of radiotelemetry for wildlife studies. This chapter provides an overview of consider- ations for using radiotelemetry in studies of the ecology and behavior of bats. We first discuss study design and the collection of radiotelemetry data, because these affect subsequent analysis, interpretation, and inferences. We then summarize and discuss analysis options. We focus primarily on techniques for working with mov- ing bats because less attention has been given to this topic than to the use of radio- telemetry to locate roosts. Due to rapid developments in both equipment and ana- lytical procedures, bat researchers should continue to review literature and electronic sources and to consult with colleagues and equipment suppliers to re- main current. WL__ 58 S. K. AMELON, D. C. DALTON, J . J . MILLSPAUGH, AND S. A. WOLF Costs associated with radiotelemetry vary consider- DESIGN OF RADIOTELEMETRY STUDIES ably depending on the objectives of the study and data Historically, bat telemetry studies were mainly de- analysis methods selected. Simple projects to find specific scriptive. Although descriptive studies have a role for rare, roosts may be relatively inexpensive, short term, and con- elusive, or previously unstudied species, research studies ducted by a few individuals; projects to quantify home designed to quantitatively investigate relationships be- range or foraging behavior require a much larger invest- tween bats and their environment are now achievable. ment of personnel, equipment, and time to obtain ade- The first consideration when designing a quantitative quate data to make inferences. To determine the feasibil- study is to identify specific objectives and the scope of ity of a study, a budget based on study objectives, including inferences; these decisions will guide many of the re- sample size and number of relocations required, should be maining considerations, including whether radioteleme- developed early in the design process. Project cost esti- try is an appropriate tool for achieving the objectives. mates should include the purchase of equipment (trans- The population of interest, geographic area, and scale of mitters, antennas, and receivers), salaries and expenses for the proposed question will guide other decisions, includ- field personnel, and transportation (e.g., vehicles, aircraft). ing appropriate experimental units, measures of preci- If the budget is limited, some objectives will not be feasible sion for hypothesis testing or model building, and num- and either additional funding should be sought or study bers of individuals to be radio tagged (Garton et al., objectives should be reevaluated. 2001). Carefully designed studies maximize the amount and EQUIPMENT AND TECHNIQUES FOR reliability of information obtained. Key considerations in RADIOTELEMETRY PROJECTS radiotelemetry studies include selection of animals (i.e., randomly) for radio tagging, the number of animals, and Equipment for Telemetry Systems the number of locations per animal (Worton, 1995; Sea- The basic components of a radio-tracking system in- man et al., 1999). Gender, age, reproductive condition, clude (1) a transmitting system consisting of a radio trans- geographic location, and other unique characteristics con- mitter, a power source, and a propagating antenna, and (2) tribute to variability or bias; therefore, stratification by a receiving system including an antenna, a signal receiver, sex or age is recommended when inference objectives dic- and a power source. Although several types of radiotelem- tate. Most analysis methods currently available for habitat etry systems are currently used in wildlife research, in- studies assume random selection of individuals, if ran- cluding very high frequency (VHF), ultra high frequency domization and stratification are impractical, the research (UHF), satellite, and GPS, VHF radiotelemetry is the only question, study design, or type of analysis may require type currently available that meets the size and weight re- modification to overcome violations of assumptions that strictions for smaller bat species. Technology, including use may invalidate results. Analysis of movements may in- of satellite tracking and GPS telemetry, is rapidly advancing; clude differential patterns based on the individual, sex, the minimum weight of currently available equipment is age, season, and representative activity. Some bat species approximately 9.5g for solar-powered platform transmit- spend considerable time foraging in a relatively small area ter terminal (PTT) units and 20g for battery-powered (Henry et al., 2002); others move rapidly from roost sites units. GPS-enabled PTTs weigh a minimum of 30 g. These to more distant foraging areas (Kerth et al., 2001; Bonta- weights may allow use of these methods for large species dma et al., 2002). Careful consideration of these factors but render them unsuitable for smaller species. Current will aid in determining appropriate time intervals to doc- satellite technology is considered less accurate than VHF; ument movement rates and will guide the cost—and ulti- differentially corrected GPS telemetry theoretically in- mately the feasibility—of a specific study. General guid- creases accuracy to ±5m. However, CPS units are also ance is available regarding numbers of animals (Alldredge several times more expensive than standard VHF and and Ratti, 1986, 1992; Leban et al., 2001, Winterstein et al., non-GPS satellite units. These technologies hold promise 2001) and the number of locations per animal (Seaman et for future applications, as units will likely decrease in size al., 1999; Kernohan et al., 2001). Having a proposed study and expense. design reviewed by a biometrician before embarking on any field work potentially avoids costly mistakes, such as Transmitters biased data or inappropriate inferences, caused by defi- Transmitters attached to microchiropterans typically cient design. Ratti and Garton (1994) provide detailed weigh less than 1.1g (Barclay et al., 1996; Brigham et al., information on experimental design; Kenward (1987, 1997; Lacki and Schwierjohann, 2001; Willis and Brigham, 2001), White and Garrott (1990), Carton et al. (2001), 2002) and have proportionally small batteries and weak Kernohan et al. (2001), and Millspaugh and Marzluff signals that place strict requirements on the receiving (2001) provide additional information on radiotelemetry equipment, especially on the receiving antenna. Trans- design issues. mitters weighing 0.25-0.65g, with magnetic reed switch Radiotelemetry 59 or manual activation, are available from several sources mass of the transmitter, adhesive, and any other markings (Appendix 3.1). Larger transmitters, suited to larger spe- should weigh less than 5% of the preattachment weight of cies, provide significantly longer battery life and thus lon- the bat. In the case of pregnant females, special consider- ger tracking time (for bats over 75 g, a 2-3 g transmitter ation should be given to whether attachment is appro- lasts 10 weeks or longer; Fuller et al., 2005). priate at all. If the female is tagged, preattachment mass Transmitters that provide temperature measurement should be estimated from the normal mass range for the of the bat use a sensitive thermistor that varies the pulse species, or by subtracting the estimated fetal mass based rate of the transmitter. The pulse rate is determined with on fetal development (a full-term fetus may represent 20- the aid of a stopwatch and converted to a temperature us- 30% of female body mass; Hayssen and Kunz, 1996). It is, ing a calibration curve. The system is sensitive to 0.1°C therefore, important to justify the need, understand the and does not increase the volume of the transmitter. impacts, and minimize complications of transmitters for Telemetry studies of small bats typically use surgical scientific, economic, humanitarian, and legal reasons glue or a similar nonirritating adhesive to attach the trans- (Murray and Fuller, 2000; Withey et al., 2001). A "com- mitter between the scapulars (Wilkinson and Bradbury, mon sense" rule is used by many researchers: (1) always 1988). Some species are particularly adept at grooming the consider the ethics of attaching tags; (2) consider the be- transmitter off before the transmitter fails.