Assessing heart rate in an apex predator: piloting biologging in jaguars (Panthera onca)

As top predators, jaguars ( Panthera onca ) are key drivers of ecosystem health and particularly vulnerable to habitat disturbances, whether arising from natural processes or anthropogenic impacts. Yet, their physiological responses to increasing environmental pressures and habitat loss remain poorly understood. Because physiological stress and changes in metabolic processes can occur before visible behavioral alterations or population declines, physiology offers a valuable early-warning metric for conservation. Among physiological indicators, heart rate (HR) is a practical and informative parameter that reflects both acute and chronic responses to environmental change. Incorporating HR monitoring via biologging can enhance our understanding of how individuals respond to stressors. Consequently, understanding how apex predators respond to environmental and management-related factors from a physiological perspective, including HR, is important not only to assess how individuals cope with change, but also to predict potential population declines or shifts in trophic interactions, thereby improving conservation strategies. Yet, even baseline cardiac parameters remain undefined for most species, and existing references are often limited to anesthetized animals. We used jaguar ( Panthera onca ) as a model for advancing HR monitoring approaches in keystone species. We present the first validation and long-term assessment of HR in conscious, unrestrained captive jaguars using an insertable cardiac monitor (ICM). We successfully collected data from seventeen jaguars, implanted with the Reveal LINQ™ device at two Brazilian facilities (NEX and AMPARA). After excluding one individual with persistent T-wave oversensing artifacts, 16 animals yielded high-quality HR recordings with a mean duration of 375 days. Mean HR over 2-minute intervals across all individuals was 85 ± 28 bpm (range 31–250). Using generalized additive models, we identified activity as the strongest HR predictor, followed by time of day, ambient temperature, season, and weekday versus weekend. Jaguars exhibited daily rhythms, with HR and activity peaks between 05h00–06h00 and 16h00–20h00, the latter aligning with feeding schedules and reflecting anticipatory behavior. These findings validated the ICM as a safe and reliable tool for jaguar cardiac monitoring, established a natural baseline for monitoring stress responses to anthropogenic threats in free-ranging populations, and provided a quantitative framework for optimizing ex situ welfare.