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Daily torpor is frequently expressed in small rodents when facing energetically unfavorable ambient conditions. Desert hamsters (Phodopus roborovskii, similar to 20 g) appear to be an exception as they have been described as homeothermic. However, we hypothesized that they can use torpor because we observed reversible decreases of body temperature (T-b) in fasted hamsters. To test this hypothesis we (i) randomly exposed fasted summer-acclimated hamsters to ambient temperatures (T(a)s) ranging from 5 to 30 degrees C or (ii) supplied them with different rations of food at T-a 23 degrees C. All desert hamsters showed heterothermy with the lowest mean T-b of 31.4 +/- 1.9 degrees C (minimum, 29.0 degrees C) and 31.8 +/- 2.0 degrees C (minimum, 29.0 degrees C) when fasted at T-a of 23 degrees C and 19 degrees C, respectively. Below T-a 19 degrees C, the lowest T-b and metabolic rate increased and the proportion of hamsters using heterothermy declined. At T-a 5 degrees C, nearly all hamsters remained normothermic by increasing heat production, suggesting that the heterothermy only occurs in moderately cold conditions, perhaps to avoid freezing at extremely low T(a)s. During heterothermy, T(b)s below 31 degrees C with metabolic rates below 25% of those during normothermia were detected in four individuals at T-a of 19 degrees C and 23 degrees C. Consequently, by definition, our observations confirm that fasted desert hamsters are capable of shallow daily torpor. The negative correlation between the lowest Tbs and amount of food supply shows that heterothermy was mainly triggered by food shortage. Our data indicate that summer acclimated desert hamsters can express fasting-induced shallow daily torpor, which may be of significance for energy conservation and survival in the wild. (C) 2016 Elsevier Inc. All rights reserved.