Localizing Japanese toads in a mountainous terrain using drone-based radiotelemetry

Abstract

Monitoring the movement of small animals is a fundamental aspect of ecological studies as well as spatially explicit conservation and management. However, this remains a challenging task especially in mountainous terrains. Although drone-based radiotelemetry (DRT) is employed to localize animals, its application in mountainous terrains is limited by the collision risks associated with undulating terrains as well as the obstruction of signals by dense vegetation and steep slopes. We addressed these challenges by generating fine-scale three-dimensional maps and moving vertically mounted directional antennas in a double grid pattern, scanning both in longitudinal and latitudinal grids. This new DRT system was helpful in localizing four adult Japanese toads ( Bufo japonicus) living in hiding places typical of mountainous terrains. All toads were located within 1–60 days of being released. Transmitter signals were detected within two consecutive flights (three flights in one case). Instances of transmitter detection were significantly biased when the drone was facing either direction of the double-grid path, indicating that the double-grid pattern had reduced detection failure. The absolute localization error ( n = 48) of 22.4 ± 21.0 m (44.8 ± 42% of the transmitter-to-receiver distance) was lower than that reported in a previous study conducted in a similar mountainous terrain.