Pulse of the Arctic: feasibility of long-term physiological monitoring of polar bears using implantable heart rate and temperature loggers

Abstract Background Energy expenditure shapes key biological functions in animals, including reproduction, growth, foraging, and survival. Yet quantifying energy expenditure over long periods in wildlife, especially in remote Arctic environments, remains difficult. Traditional approaches of estimating metabolic rate using heart rate (HR) measurements by external devices have substantial limitations, whereas implantable biologgers offer a promising alternative. This study assesses for the first time the feasibility of using implantable heart rate and temperature (HRT) loggers in wild adult female polar bears (Ursus maritimus) equipped with GPS collars in the Svalbard Archipelago. Results Five bears were surgically implanted with HRT devices that recorded HR and body temperature every 15 min for more than a year, along with short (4 s) and long (10 s) electrocardiograms (ECG) every 6 h and 18 h, respectively. The females were tracked using GPS collars throughout the study. All implantation procedures were completed safely, and device retrieval the following year revealed no lasting health effects. The loggers performed reliably, with 82% of HR data classified as high quality. Manual validation of ECGs increased data retention by 1.7% and verified the accuracy of extreme HR values (11 to 178 BPM). Lower-quality data were generally associated with shorter ECG durations and low HR, although variation among individuals suggests that motion artifacts or muscle electrical activity also contributed. Minimal heat loss occurred at the shaved implantation site, and subcutaneous temperature stabilized within 2–5 days. Conclusions Overall, the study demonstrates that implantable HRT loggers are an effective tool for long-term recording of heart rate and sub-cutaneous temperature in wild polar bears. Future deployments should prioritize longer ECG durations (10 s) to maximize data quality.