Aimee Tallian, Norwegian Institute for Nature Research

Understanding how animals interact with one another is a fundamental goal of ecology. Although studying interactions between free-ranging animals is challenging, the advent of high-resolution GPS tracking technology has helped increase our understanding of multi-individual and multi-species behavior in wild systems. Proximity sensors for GPS collars are a novel technology that allow for detailed study of focal individuals. Proximity sensors both transmit and detect weak ultra-high frequency (UHF) signals. When a UFH signal is detected, the GPS collar will ‘trigger’ and switch to an alternate fix rate for a pre-defined time interval. In other words, collars normally set to a coarse fix rate (e.g., 1 hour) can switch to a finer-scale fix rate (e.g., 1 minute) for a specified time period when they come in the ‘proximity’ of another UHF transmitter device. Proximity sensors therefore offer the possibility to switch GPS collars to collect fine-scale GPS data during specific events and then switch back to coarser fix rates once the event is over saving battery, extending collar life, and delaying invasive, time-intensive, and costly recapture events. Here, we showcase the use of proximity sensors in several studies on brown bear predation in Scandinavia. The first study deployed proximity sensor equipped GPS collars on brown bears in Norrbotten, Sweden to evaluate bear predation on reindeer, which were equipped with simple UHF transmitters. The second study is currently deploying proximity sensor equipped GPS collars on brown bears and moose, and potentially wolves and red deer in the future, in the Ljusdal Municipality, Sweden with a goal of opportunistically collecting fine-scale movement data during direct interactions between the two species. To the best of our knowledge, this is the first time that GPS proximity collars have been simultaneously deployed on two free-ranging species to detect interspecific interaction events and record fine-scale movement in the wild.