Introduction of an automatic and open-source radio-tracking system for small animals

Movement ecology of small wild animals is often reliant on radio-tracking methods due to the size and weight restrictions of available transmitters. In manual radio telemetry, large errors in spatial position and infrequent relocations prevent the effective analysis of small-scale movement patterns and dynamic aspects of habitat selection. Automatic radio-tracking systems present a potential solution for overcoming these drawbacks. However, existing systems use customized electronics and commercial software or exclusively record presence/absence data instead of triangulating the position of tagged individuals. We present a low-cost automatic radio-tracking system built from consumer electronic devices that can locate the position of radio transmitters under field conditions. We provide information on the hardware components, describe mobile and stationary set-up options, and offer open-source software solutions. We describe the workflow from hardware setup and antenna calibration, to recording and processing the data and present a proof of concept for forest-dwelling bats using a mixed forest as study area. With an average bearing error of 6.8 degrees and a linear error of 21 m within a distance ranging from 65 m to 190 m, the accuracy of our system exceeds that of both traditional methods as well as manual telemetry. This affordable and easy-to-use automatic radio-tracking system complements existing tools in movement ecology research by combining the advantages of lightweight and cost-efficient radio telemetry with an automatic tracking set-up.