Development and utilization of implantable cardiac monitors in free-ranging American black and Eurasian brown bears: System evolution and lessons learned

Biologgers can be used to monitor both human and animal physiology and behaviors, activity patterns, and/or environmental stressors. Monitoring of heart rates and rhythms, respiratory patterns, and activity in free-ranging bears can provide unique insights into physiological mechanisms. Such research can also influence the conservation of wildlife, the management of human-wildlife conflicts, and potentially human medicine. Here we describe our experiences with the development and utilization of three generations of implantable biologgers in American black and Eurasian brown bears (Ursus americanus and Ursus arctos arctos). These devices have enabled novel investigations into the underlying mechanisms for winter survival, including the discovery of an extreme respiratory sinus arrhythmias that acts to conserve energy while providing adequate circulation to maintain alertness (i.e., "fight or flight" behaviors). Extreme variations in heart rate have also been documented, including a 33.8s asystole and a 261beats/min sinus tachycardia in black bears and a 39.4s asystole and a 240beats/min sinus tachycardia in brown bears. Long-term data recording has also identified annual trends in heart rates and activity in both species. Combining physiological data with concurrent GPS collar locations provided insights into the impacts of human and environmental stressors (hunting, predation by other bears, road crossings, drones), which would not have been apparent through spatial data analysis alone. More recently, short-range wireless telemetry has allowed for real-time streaming of data via telemetry stations placed in remote den locations. Future iterations include transponders for biomonitoring and as an early warning system to aid in the prevention of poaching in free-ranging animals. In this review, we discuss the primary experimental capabilities of the current and next-generation systems. We highlight device evolution in terms of new physiological measurements (e.g., temperature, activity, impedance, posture), increased data storage capacity, improved wireless capabilities, and miniaturization to reduce the invasiveness of implantation procedures. These biologgers are now being applied to other species, and the possibilities seem limitless as technologies continue to advance.