Seasonal and diel variation in body temperature and heart rate of the Eurasian beaver

Knowledge concerning diel and seasonal variation of body temperature and metabolic rates can provide useful information concerning the physiology, ecology, and behavior of animals and how they are adapted to living in cold conditions. Here, we investigated seasonal and diel variation in body temperature (T b ) and heart rate (HR) of Eurasian beavers ( Castor fiber ) in a region characterized by cold winters. Our aims were to better understand if (1) T b and HR vary seasonally depending on climatic conditions, (2) if these measures can be used to estimate daily activity periods, and if T b can be used to detect (3) the timing of parturition and (4) potential stress responses to GPS-tagging. We implanted body temperature- and heart rate loggers in 28 beavers in two study areas located in southeastern Norway, obtaining usable HR data for 5 individuals and T b data for 10 individuals. We demonstrate that beavers have pronounced diel and seasonal patterns of T b and HR, although seasonal changes in T b were much less pronounced than compared to hibernators. Furthermore, HR data may be used to estimate activity budgets and T b can potentially be used to identify parturition timing, tagging effects and potentially other stressors. These findings increase our understanding of the physiology and behavior of beavers, especially when inside the lodge and during winter, when behavioral or ecological studies are limited. Moreover, they provide novel data concerning the exact date of parturition, which will be useful for wildlife management.