Assessing the potential of subcutaneous biologging tools for physiological monitoring in a large terrestrial mammal, the Guanaco ( Lama guanicoe )

Abstract

Physiological responses of animals to environmental and anthropogenic stressors are fundamental to effective conservation and wildlife management. Continuous monitoring of heart rate (HR) and body temperature yields key information on energy expenditure, stress, reproduction and health status. However, acquiring long-term physiological data from free-ranging large mammals remains technically challenging. Subcutaneous implantable biologgers represent a promising approach, yet concerns about device retention, data quality and animal welfare can constrain their widespread adoption. In this study, we assessed the feasibility of subcutaneous biologging to monitor HR and subcutaneous body temperature in guanacos (Lama guanicoe), the largest wild ungulate in South America and a species currently facing increasing anthropogenic threats. Two implantation trials were performed in captive adult females, each employing distinct biologger models and surgical techniques. The initial trial, which used a larger device implanted in the pectoral region, resulted in complete device expulsion within 4 weeks, despite successful surgeries and apparent normal wound healing. Conversely, the second trial, utilizing a smaller logger implanted in the intercostal region, achieved full device retention throughout the deployment period, with minimal tissue reaction and successful data retrieval. While the results suggest that device size and implantation site are influential, the simultaneous variation in multiple aspects of experimental design prevents a definitive attribution of retention success to a single variable. The retained devices provided the first continuous records of HR and subcutaneous body temperature in this species, revealing pronounced daily rhythms and temperature patterns that correlated with ambient temperature. Overall, these results underscore the necessity of species-specific pilot validation before field deployment to minimize study failure and ensure animal welfare. By outlining practical considerations for implantable biologging in large ungulates, this study provides insight to help guide the development of physiological monitoring protocols for future field applications.