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

Although the advent of high-resolution GPS tracking technology has helped increase our understanding of individual and multi-species behavior in wildlife systems, detecting and recording direct interactions between free-ranging animals remains difficult. In 2023, we deployed GPS collars equipped with proximity sensors (GPS proximity collars) on brown bears (Ursus arctos) and moose (Alces alces) as part of a multi-species interaction study in central Sweden. On 6 June, 2023, a collar on an adult female moose and a collar on an adult male bear triggered on each other's UHF signal and started collecting fine-scale GPS positioning data. The moose collar collected positions every 2 minutes for 89 minutes and the bear collar collected positions every 1 minute for 41 minutes. On 8 June, field personnel visited the site and found a female neonate moose carcass with clear indications of bear bite marks on the head and neck. During the predation event, the bear remained at the carcass while the moose moved back and forth, moving towards the carcass site about 5 times. The moose was observed via drone with 2 calves on 24 May and with only one remaining calf on 9 June. This case study describes, to the best of our knowledge, the first instance of a predation event between two free-ranging, wild species recorded by GPS proximity collars. Both collars successfully triggered and switched to finer-scaled GPS fix rates when the individuals were in close proximity producing detailed movement data for both predator and prey during and after a predation event. We suggest that, combined with standard field methodology, GPS proximity collars placed on free-ranging animals offer the ability for researchers to observe direct interactions between multiple individuals and species in the wild without the need for direct visual observation.

尽管高分辨率GPS追踪技术的问世，助力我们加深了对野生动物系统中个体及多物种行为的认知，但检测并记录自由活动野生动物间的直接互动仍颇具挑战。2023年，我们在瑞典中部开展一项多物种互动研究，为棕熊（Ursus arctos）与驼鹿（Alces alces）佩戴了搭载近距离传感器的GPS项圈（GPS proximity collars）。2023年6月6日，一只成年雌性驼鹿的项圈与一只成年雄性棕熊的项圈相互触发对方的UHF信号，随即开始采集细粒度GPS定位数据。该驼鹿项圈每2分钟采集一次定位数据，持续89分钟；该棕熊项圈每1分钟采集一次定位数据，持续41分钟。2023年6月8日，野外研究人员前往该监测位点，发现一具雌性新生驼鹿幼崽的尸体，其头部与颈部带有清晰的熊类咬痕。在此次捕食事件过程中，棕熊始终停留于尸体位点，而驼鹿则在周边往复移动，先后5次靠近该位点。5月24日的无人机监测显示，该驼鹿携带有2只幼崽；而6月9日的无人机监测则显示，其仅剩余1只幼崽。据我们所知，本案例研究首次借助GPS近距离感应项圈记录到自由活动的野生跨物种捕食事件。当两只个体近距离接触时，两个项圈均成功触发并切换至更高采样频率的GPS定位模式，为捕食事件发生期间及结束后的捕食者与猎物提供了详尽的活动轨迹数据。我们认为，若将此类GPS近距离感应项圈与标准野外研究方法相结合，可为研究人员提供无需直接目视观测，即可记录野外多个体、跨物种直接互动的可行方案。