, Volume 168, Issue 3, pp 233-239

Daily torpor and energetics in a tropical mammal, the northern blossom-bat Macroglossus minimus (Megachiroptera)

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Little is known about torpor in the tropics or torpor in megachiropteran species. We investigated thermoregulation, energetics and patterns of torpor in the northern blossom-bat Macroglossus minimus (16 g) to test whether physiological variables may explain why its range is limited to tropical regions. Normothermic bats showed a large variation in body temperature (T b) (33 to 37 °C) over a wide range of ambient temperatures (T as) and a relatively low basal metabolic rate (1.29 ml O2 g−1 h−1). Bats entered torpor frequently in the laboratory at T as between 14 and 25 °C. Entry into torpor always occurred when lights were switched on in the morning, independent of T a. MRs during torpor were reduced to about 20–40% of normothermic bats and T bs were regulated at a minimum of 23.1 ± 1.4 °C. The duration of torpor bouts increased with decreasing T a in non-thermoregulating bats, but generally terminated after 8 h in thermoregulating torpid bats. Both the mean minimum T b and MR of torpid M. minimus were higher than that predicted for a 16-g daily heterotherm and the T b was also about 5 °C higher than that of the common blossom-bat Syconycteris australis, which has a more subtropical distribution. These observations suggest that variables associated with torpor are affected by T a and that the restriction to tropical areas in M. minimus to some extent may be due to their ability to enter only very shallow daily torpor.

Accepted: 22 September 1997