DAILY TORPOR AND ENERGETICS IN A TROPICAL MAMMAL, THE NORTHERN BLOSSOM-BAT MACROGLOSSUS-MINIMUS (MEGACHIROPTERA)

Little is known about torpor in the tropics or torpor in megachiropter an species. We investigated thermoregulation, energetics and patterns of torpor in the northern blossom-bat Macroglossus minimus (16 g) to t est whether physiological variables may explain why its range is limit ed to tropical regions. Normothermic bats showed a large variation in body temperature (T-b) (33 to 37 degrees C) over a wide range of ambie nt temperatures (T(a)s) and a relatively low basal metabolic rate (1.2 9 mi O-2 g(-1) h(-1)). Bats entered torpor frequently in the laborator y at T(a)s between 14 and 25 degrees C. Entry into torpor always occur red when lights were switched on in the morning, independent of T-a. M Rs during torpor were reduced to about 20-40% of normothermic bats and T(b)s were regulated at a minimum of 23.1 +/- 1.4 degrees C. The dura tion of torpor bouts increased with decreasing T-a in non-thermoregula ting bats, but generally terminated after Sh in thermoregulating torpi d bats. Both the mean minimum T-b and MR of torpid M. minimus were hig her than that predicted for a 16-g daily heterotherm and the T-b was a lso about 5 degrees C higher than that of the common blossom-bat Sycon ycteris australis, which has a more subtropical distribution. These ob servations suggest that variables associated with torpor are affected by T-a and that the restriction to tropical areas in M. minimus to som e extent may be due to their ability to enter only very shallow daily torpor.