Proximity-sensors on GPS collars reveal fine-scale predator-prey behavior during a predation event: A case study from Scandinavia

Bears and female moose were captured and collared via helicopter using established protocols (Kreeger and Arnemo 2007, Arnemo et al. 2012, Lian et al. 2014), which were approved by the Swedish Ethical Committee on Animal Research; Permits Dnr 5.8.18-03376/2020 and Dnr A11-2020. Moose capture efforts began in 2020, with the goal of collaring females near the 2018 burn and within the core study area (Fig. 1). Bear capture efforts began in 2022 and were focused on the area where moose had previously been collared to maximize temporal and spatial overlap between species and thus, the potential to observe interspecific interactions. Captured bear and moose were equipped with GPS neck collars (Vectronic Aerospace, 2023). During the 2023 capture, a sub-sample of bears (n = 4; 2 adult males, 1 solitary female, and 1 female with cubs of the year) and moose (n = 18) were fit with GPS neck-collars that also had proximity sensors and UHF transmitters, i.e., GPS proximity-collars (Vectronic Aerospace GmbH, Berlin, Germany). Proximity collars are equipped with a UHF transmitter and receiver; the transmitter sends a weak UHF signal while the receiver scans for other UHF signals (see Table 1 for detailed settings). Once a signal was received by a collar, the collar reconfigured to a pre-determined fix schedule and logged the ID of the collar that it was triggered by. Once the signal was lost, the collar reverted to its original programming after a pre-scheduled amount of time. The range of UHF signal detection is based on terrain and cover but is usually about 100 m or so away. Bear proximity collars were programmed to take GPS positions every 30 minutes and increase to a fixed rate of 1 position every 1 minute for a duration of 15 minutes when they came within range of another UHF signal (Table 1). Moose proximity collars were programmed to take GPS positions every 30 minutes and increase to a fixed rate of 1 position every 2 minutes for a duration of 60 minutes when they came within range of a proximity-collared bear; the 2-minute setting was chosen to save battery life over the longer fix duration. Using the GSM-network or IRIDIUM satellite, the collars send continuously positions to the existing database Wireless Remote Animal Monitoring (Dettki et al. 2014) at the Swedish University of Agricultural Sciences, which allows us to monitor animals remotely in near real-time.