Many small mammals employ hibernation or daily torpor to reduce energy expenditure by lowing metabolic rate and body temperature. Although it is known that the reduction of metabolic rate is more pronounced during hibernation than during daily torpor, it is unclear whether different physiological processes contribute to metabolic rate reduction during the two patterns of torpor. In addition, differences in relation to behaviour and energy expenditure between hibernation and daily torpor are not well understood. To determine physiological difference between hibernation and daily torpor, a detailed investigation was conducted by using two similar-sized small marsupials, 'Cercartetus nanus', a hibernator, and 'Sminthopsis macroura', a daily heterotherm. Thermophysiological variables, including metabolic rate, body temperature, thermal differential between body temperature and ambient temperature, and conductance of the two species were measured under the same experimental conditions. Interrelations between these variables during both normothermia and torpor were analysed over a wide temperature range. Torpor entry, steady-state torpor, and arousal were distinguished in the analyses. In addition, temperature selection and locomotor activity in relation to the use of torpor were investigated. Energy expenditure in response to duration of torpor and arousal was also compared. ... The thermal and metabolic characteristics of 'C. nanus' and 'S. macroura' indicate that different physiological adjustments are involved in hibernation and daily torpor to achieve energy conservation.

Marsupial mammals living in temperate regions must cope with environmental stresses imposed by daily and seasonal changes in climate. However, limited information is available on seasonal adjustments of thermal physiology, morphology and behaviour of this mammalian subclass. The sugar glider, 'Petaurus breviceps', is a small, nocturnal marsupial (115-140 g) which inhabits the east coast of Australia, including the New England Tablelands, a cool-temperate region with marked daily and seasonal changes in ambient temperature (Ta). Consequently, this species is often subjected to high energetic stress. To see how they respond to energetic challenges, gliders were maintained under natural Ta and photoperiod. Metabolic rates, body temperature (Tb), thermal conductance, locomotor activity, body mass, body composition, and food consumption were determined throughout the year.