Metabolic rate is a fundamental property that reflects the total energy demand for all aspects of organismal function, from immune performance to reproduction. Metabolic rate scales allometrically with body mass and varies with diet, tending to be lower for herbivores and large-bodied insectivores, and higher for carnivores specializing in vertebrate prey. In this study, we are examining the resting metabolic rate (RMR) of two Ursidae species at the Cambodia Bear Sanctuary supported by Free the Bears and located within the Phnom Tamao Wildlife Rescue Center in Cambodia. We are focused on two species that are divergent in body size and life history traits – the Asiatic black bear (Ursus thibetanus) and sun bear (Helarctos malayanus). Asiatic black bears are larger (110 kg versus 50 kg for sun bears) and are less insectivorous than sun bears, suggesting that their RMR may be lower. However, RMR may also be affected by the climate at our study site. Asiatic black bears are primarily distributed in temperate regions and our study site is close to their most southern and tropical extent, whereas sun bears primarily occur in tropical regions and are thus presumably better-adapted to the study site climate. This raises the possibility that the warm climate at our study site may result in a higher RMR for Asiatic black bears. Using flow through respirometry we are collecting measurements of resting VO2 and VCO2 of both species at the Rescue Center. We are repeating measurements on the same individuals within field seasons to assess intra-individual variation, and between seasons (December, cooler; May, warmer) to test for seasonal variation.