Continuous records of body temperature (Tb) and oxygen consumption were used to investigate the influence of daily torpor on energy requirements in Djungarian hamsters (Phodopus sungorus) exposed to ambient temperatures (Ta's) between O° C and 20° C During torpor Tb was lowered to values between 14.0 °C and 31.3°C for variable periods (0.3-9.2 h; mean, 5.4 ± 0.23 h). Average daily metabolic rates (ADMRs) were inversely related to Ta in both hamsters exhibiting torpor and animals staying normothermic and can be predicted from their linear relation to mean daily (Ta − Tb)-gradients. The torpor-induced reduction of ADMRs below normothermic values was directly related to torpor depth and duration, withprolonged torpor episodes (>4 h) causing a 20.2% ± 0.9% saving in energy. Thus, daily torpor reduces metabolic costs to a level approaching the resting metabolic rate of normothermic hamsters (24% below ADMR) and helps compensate for the energetic costs of locomotor activity. Individuals with a high tendency to enter torpor also save substantial amounts of energy by lowering average metabolic rates during the normothermic phase of the day. Calculations based on these data show that daily torpor in Djungarian hamsters may serve to allow the continuation of foraging at low Ta's during winter in the Siberian steppe.
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Ruf et al. (1992) studied this question.
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