The digital mobile and adjustable telemetry system being introduced may benefit researchers lacking a dedicated vehicle in which permanent alterations can be made. The construction of DMATS is simple and can be accomplished in a relatively short period of time given the necessary materials and tools are available. The cost for materials is small. However, the electronic compass, the most costly portion of the equipment, can be substituted with a compass rose that has some type of pointed object that has been aligned with the main tine of the antenna that can be used to indicate the bearing on the compass rose. If this is not an option, the user can utilize a handheld compass by exiting the vehicle and taking a reading by aligning the handheld compass bearing with the main tine of the antenna. Both methods, which will lower the cost of DMATS, also come with the potential for increasing the probability of increased human error in acquiring a bearing when compared to that of an electronic compass. Kenward (2001) described methods to construct a traditional mobile system, which requires a permanent hole to be placed in the roof of the vehicle's cabin, and estimated the cost to be $2100–$4200 USD (these amounts have been adjusted to 2012 values). Far more expensive than the $1059 USD needed for the construction of DMATS.
The accuracy and precision of DMATS were important factors when designing this system. We defined accuracy as the ability of the device to correctly identify the true location of the telemetry collar and precision as the ability of DMATS to identify the true location of the telemetry collar repeatedly. We assessed the accuracy of DMATS by the size of error ellipses and the bias between the estimated location of the collar and the true coordinates of the radio collar. Additionally, we assessed precision by examining the standard deviations associated with the error ellipses and the distribution of estimated locations.
The absence of statistical difference in the size of error ellipses between the handheld system and DMATS indicated that the precision of DMATS proved to be equivalent to that of the handheld telemetry system. However, even though there was variation in the size of error ellipses between users the standard deviations, which is the measure of precision for telemetry (Saltz 1994; Kenward 2001; Fuller et al. 2005), remained relatively small for each tester (Table 2). Demonstrating the precision, or repeatability, of the system. Furthermore, even with the variation in the sizes of error ellipses, the areas within the error ellipses overlapped. It is those areas of overlap that contained the true location of the test collar.
We believe the primary cause for variation in error ellipses was due to the differing levels of experience between the testers and topographic features of the area used for testing the system. In difficult terrain, detecting the direction of the strongest signal can be challenging for the most experienced technician (Kenward 2001). However, when combining the topography with the presence of electrical power lines, such as those located within and surrounding the test location, and more specifically, those near testing stations, signal deflection may have increased substantially. Therefore, making the detection of the actual location of the collar difficult to distinguish—especially by a less experienced user.
We believe some features of DMATS may help minimize mistakes by the less experienced user. In most cases, the more experienced user will be knowledgeable of methods to reduce some biases associated with telemetry, however, the ability to adjust antenna height and the use of an electronic compass may compensate for the lack of experience. The ability to adjust the antennae is critical to getting the strongest signal reception (Kenward 2001; Fuller et al. 2005). In challenging habitats, especially those with increased signal deflection, less experienced users can become frustrated trying to identify the bearing of the signal. Having the ability to not just move the antennae horizontally but also vertically will greatly increase the ability of the user to detect the true signal bearing.
Mountainous, afforested, and urban areas can prove to be quite challenging for telemetry studies. Kenward (2001) noted difficulties in identifying a bearing because of signal deflection in areas with considerable amount of tree cover. However, while testing DMATS in an urban setting, we also took note of the sizeable amount of signal deflection. Given the inherent characteristics of urban settings, increased electrical wiring and high concentrations of impervious surfaces, the occurrence of signal deflection may be a continuous. As such, this will almost certainly create difficulties in determining the true bearing of transmitting devices. However, we believe, in addition to the adjustable antenna height, the use of the electronic compass, may make the task of achieving a true signal bearing more attainable for less experienced users. While testing DMATS, the electronic compass allowed the user to focus on correctly identifying the direction of the strongest signal reception without the distraction of determining the bearing using a compass rose or a prismatic compass.
Mobile telemetry systems possess an advantage over handheld telemetry systems by allowing the user to move more rapidly between sampling areas. Additionally, the use of a vehicle removes the constraints of the weight and difficulty associated with carrying added equipment or a larger antenna. Our mobile telemetry system provides the traditional advantage over handheld telemetry while also providing adaptability not found with other vehicle-mounted systems. The DMATS system allows the user to cover multiple terrain types by simply moving the system to an appropriate vehicle. Users who may otherwise track animals with a handheld system due to an inability to modify a vehicle or multiple vehicles can utilize DMATS to decrease search time and increase search range.
As an added benefit, although not tested empirically, we believe the use of DMATS increased the speed in which readings can be taken when compared to that of a handheld system. We make this assumption because DMATS allows the operator to take a bearing from the driver's seat of the vehicle, eliminating the time used to park and exit the vehicle. This can be important when performing telemetry in urban settings or other areas where the necessary locations to take readings may be unsafe for vehicles to be stopped for prolonged instances. Additionally, the use of the digital display of the electronic compass also increased efficiency by reducing the amount of time that would be needed to determine a compass bearing. This may be of greater importance when tracking highly mobile species and minimizing time between readings is important.