Bats of the mammalian order Chiroptera make up about one-fifth of all mammal species and a large proportion of bat species inhabit subtropical and tropical regions. Most bats, particularly microchiropterans, weigh well under 25 g and therefore expend large amounts of energy for normothermic thermoregulation. Consequently, many microchiropterans are heterothermic endotherms and use torpor for energy conservation. However, despite the large number of species inhabiting subtropical and tropical regions knowledge about torpor use in free-ranging subtropical and tropical microbats is scarce. This is largely due to the view that low and stable ambient temperatures (Ta) are necessary for torpor use. The aim of my project was to collect data on the skin temperature (Tskin) of free-ranging insectivorous northern long-eared bats ('Nyctophilus bifax'), which are restricted to the Australian tropics and subtropics. This was accomplished via temperature-telemetry. As weather, food availability and reproduction vary seasonally, I undertook seasonal studies on 'N. bifax' at a subtropical field site, because detailed knowledge on how free-ranging subtropical insectivorous bats cope with such changes is essentially non-existent. Winter studies were undertaken on 'N. bifax' in two different habitats, a subtropical region near the southern end of their range and a tropical region near the northern end of their range to determine whether they employ torpor and especially prolonged torpor, and also whether their thermal physiology varies within their range. Additionally, since few studies have examined the thermal energetics of torpor in species that inhabit only subtropical and tropical regions, I quantified the thermal energetics of 'N. bifax' during summer, winter and spring from a subtropical habitat and also during winter from a tropical habitat.