Heart rate biologging as a tool to understand the energetic needs of life history states.

Energy is vital for life, and the energetic needs of an organism can be quantified via its metabolic rate, for which measurements have traditionally been restricted to the laboratory. Alternatively, heart rate has been shown to be an excellent predictor of metabolic rate under laboratory conditions and can provide long-term measurements from free-ranging individuals at fine temporal resolution. We quantified the relationship between metabolic rate, heart rate and body temperature of a small arboreal marsupial, Krefft's glider (Petaurus notatus; ~125 g) and how their energetic needs are affected by reproductive condition. Gliders were housed in a large outdoor aviary that experienced natural weather variations. We measured heart rate and body temperature continuously with internal implanted data loggers, and metabolic rates were intermittently measured in a laboratory with open flow respirometry. In addition to establishing a positive curvilinear relationship between heart rate and metabolic rate, these data were also used to calculate daily energy expenditure while gliders were in the outdoor aviaries. Daily energy expenditure decreased from winter to spring, indicating a strong seasonal influence, which likely resulted in lactating females utilizing less energy during spring than gestating females during winter. Understanding the energetic requirements of species under different life history states is vital for understanding their ecology and ultimately conservation management.