Fingerprint localisation for fine-scale wildlife tracking using automated radio telemetry

1: Automated radio telemetry systems are among the most widely applicable method for tracking wildlife at fine spatiotemporal scales. These systems are increasingly applying large networks of simple receivers to detect radio signal strength (RSS) from radio tagged individuals. Analytical methods to derive position estimates using RSS localisation, however, are relatively underdeveloped in the field of wildlife tracking. Here, we apply approaches from indoor positioning systems to develop a new method, radio fingerprinting, for localizing radio tagged animals in structurally complex, outdoor environments. This method characterizes the RSS patterns at known locations to generate a radio map of the study area, which is then used to predict the location of new RSS patterns. 2: We conducted field tests to evaluate the localisation accuracy of radio fingerprinting relative to multilateration, a commonly used method for RSS localisation. To do so, we established an experimental receiver network covering multiple habitat types and compared the localisation accuracy of radio fingerprinting to multilateration. Additionally, we evaluated how a variety of features characteristic of typical tracking datasets affected the accuracy of both methods. 3: While both methods had a similar median error (~30 m), the fingerprint localisation method offered several advantages over multilateration. Multilateration localisation estimates were highly affected by missed detections from the nearest receiver to the test point, which occurred in 30% of cases. In these cases, the median error was 97 m, over a 3-fold increase. Distance to the nearest receiver also biased multilateration estimates with error increasing as the distance increased. Additionally, errors from multilateration estimates were higher in more densely vegetated areas. In contrast, fingerprinting position estimates were largely robust to each of these scenarios. 4: Automated radio telemetry enables the fine-scale, continuous tracking of range-resident animals. We present radio fingerprinting as a localisation method in outdoor environments where standard localisation methods may be inadequate. This approach can be applied to any automated radio telemetry hardware and to any study system where a radio map can be generated.