Performance Characteristics of Small Global-Positioning-System Tracking Collars

Abstract

Recent technological advances have made possible the development of animal-tracking devices based on the global positioning system (GPS) that are much smaller than what were available previously. However, potential limitations in size-dependent technologies and differences in patterns of behavior between small and large animals could mean that miniaturized GPS tracking devices may not function as well as their larger counterparts. Here, we evaluate the performance characteristics of 105-g GPS collars suitable for prolonged use on animals weighing as little as 2.5 kg. We tested 9 collars in stationary trials at a single reference site and in field deployments on common brushtail possums ( Trichosurus vulpecula/ ), a semi-arboreal, nocturnal marsupial. We found in both trials that individual collars differed in several measures of positional accuracy and precision, yet overall the small collars compared favorably with published results of larger devices in similar habitats. Differences in operational characteristics between the two trials were mainly in the number and spatial configuration of satellites used to calculate position fixes, resulting in an increase in median location error from 9.8 m in the stationary tests to an estimated 14.7 m in the field trials. Most probably, these effects were due to dissimilarities in microhabitat features and variation in the orientation of GPS antennae which occurred when the possums changed their body posture during movement. The collars evaluated in this study promise to be a valuable tool for the study of the ecology, behavior, and conservation of many small-to-medium sized animals.