A Telemetric Monitor for Determining Animal Activity

Design details are presented for a radio transmitter, keyed on and off by an inexpensive motion transducer. A piezoelectric element from a phonograph pickup cartridge and two steel balls create voltages which trigger the transmit circuits whenever the unit is moved. In use, the transmitter quantifies animal activity and permits nonvisual monitoring of daily, seasonal, and annual activity rhythms. It also aids in determining the effects of meterologic or physiologic conditions upon patterns of animal activity. Periodic counts of jackrabbits (Lepus californicus) along ranch roads in Texas were initiated in 1964 to serve as indices to populations. The technique was similar to that used by French et al. (1965) for this species and by Wight (1959) and Alkon (1963) for cottontails (Sylvilagus floridanus). Our count lines were run monthly and began within the first half hour after sunrise. Inspection of the data suggested that jackrabbit counts were influenced by weather, as Alkon (1965) reported for cottontails, and by changes in circadian rhythms, similar to those described for cottontails by Lord (1959, 1961). Since changes in activity patterns relative to our sight-census procedures would imply that data collected at different times were not comparable, knowledge was needed of jackrabbit activity patterns. Several limitations were encountered in adapting techniques previously used for studying the activity rhythms of free-ranging animals. Repeating sight-census techniques throughout the diurnal-nocturnal cycle (Lord 1961) provides a relative distribution of the numbers of animals seen but gives no indication of the degree of synchrony in activities of individuals or the percentage of individuals involved at any specific time. Automatic camera devices used for detecting activity patterns (Pearson 1959, Abbott and Coombs 1964) are not especially suited for use on species without well defined trail systems. Radiotracking and telemetering equipment, however, offered several possibilities. Several authors (Southern 1965, Marshall 1965) have mentioned that movements of animal-mounted transmitters can be detected through qualitative changes in the radio signals received. Mech et al. (1966) used changes in transmitter location, as determined by direction-finding "fixes," as an indication of snowshoe hare activity. Both techniques are subjective in that they require interpretations of signal quality or rely on secondary means of determining activity or quiescence. In the latter case, Mech and his associates mentioned they were limited by the resolving power of their radio direction-finding system and position changes of less than 50-200 ft could not be detected. We observed that at the beginning of an activity period, cottontails and jackrabbits frequently are active in the immediate vicinity of their forms for periods up to 45 minutes (occasionally 90 minutes) before venturing 50 ft or more from their resting places. To avoid arbitrary definitions of activity and biases inherent in subjective interpretations of radio signals, we designed a telemetric monitor to provide discrete information on animal motions.