Thermal Biology, Torpor, and Activity in Free-Living Mulgaras in Arid Zone Australia during the Winter Reproductive Season

Abstract

Little is known about the energy conservation strategies of freeranging marsupials living in resource-poor Australian deserts. We studied activity patterns and torpor of free-living mulgaras ('Dasycercus blythi') in arid central Australia during the winter of 2006. Mulgaras are small (~75 g), nocturnal, insectivorous marsupials, with a patchy distribution in hummock grasslands. Mulgaras (six males, three females) were implanted intraperitoneally with temperature-sensitive transmitters and monitored for 6–55 d. Temperature profiles for different microhabitats and the thermal properties of soil and a number of burrows were also measured. Air temperature ranged from -3°C at night to 30°C during the day. Although burrows buffered temperature extremes, the thermal diffusivity of the sandy soil was high, and many burrows were shallow. Hence, soil and burrow temperatures averaged about 15°C. The activity of mulgaras was often restricted to a few hours after sunset, before they retired into their burrows. Mulgaras employed torpor frequently, often entering torpor during the night and arousing around midday, with arousals occurring later on cooler days. Shallow burrows allowed cooling below mean Tsoil. Consequently, body temperatures as low as 10.8°C were observed. The longest torpor bout was 20.8 h. Torpor patterns changed seasonally and differed between males and females. From June to August, females entered torpor almost daily despite mating and gestation, but from the end of the gestation period onward, they remained normothermic. In contrast, males showed only shallow and short torpor during the mating season, but from mid-July, a transition to more frequent and deeper torpor resembling that of females was observed. Apparently, in both sexes, the reproductive effort entails energetic costs, but torpor, as an energy-saving mechanism, and reproduction are not exclusive in mulgaras. In a resource-poor environment during the least productive part of the year, frequent torpor seems to provide the means to compensate for the increased energetic costs associated with reproduction.