Energetics, Thermal Biology, and Torpor in Australian Bats

Abstract

Although most Australian bats have been isolated from bat species in other parts of the world for prolonged periods and may functionally differ, little detailed research has been conducted to determine how Australian bats cope with seasonal and short-term food shortages and adverse environmental conditions. This chapter provides a comparative summary about the limited information on the thermal biology and energetics of Australian bats. The data suggest that, in general, Australian bats are similar in their thermal characteristics and energy use to other bats. Thermal conductance of Australian bats is almost identical to what has been observed in other bat species, although conductance in some tropical taxa is higher than predicted. The basal metabolic rate (BMR) of Australian bats tends to be somewhat below that predicted from allometric equations for bats and, in general, is well below that of placental mammals. However, BMRs of the insectivorous/carnivorous micro bats (Microchiroptera) do not appear to differ from those of frugivorous/ nectarivorous megabats (Megachiroptera). Torpor appears to be common in Australian bats and has been observed in six of seven families: Preropodidae (blossom-bats and tube-nosed bats), Emballonuridae (sheathtail bats), Rhinolophidae (horseshoe bats), Hipposideridae (leaf nosed bats), Vespertilionidae (long-eared and benrwing hats and others), and Molossidae (free-tailed bats). Australian vespertilionids (and likely members of other families) have the ability to enter deep and prolonged torpor in winter (i.e., hibernate) and members of the genus Nvctophilus have been observed entering brief bouts of torpor in the field on every day during the resting phase, even in summer. The body temperature (T) in some vespertilionids falls to minima between 2 and 5 ' C and the metabolic rate (MR) during torpor can be as low as 3-4% of BMR. Small megabats (e.g., blossom-bats) enter daily torpor, their T falls to a minimum of 17-23 °C and their MR to about 50% of BMR. Unlike many other species, torpor in blossom-bats is more pronounced in summer than in winter, likely clue to the low supply of nectar during the warm season. The low BMR and the high proclivity of Australian bats for using torpor suggest that they are constrained by limited energy availability and that heterothermy plays a key role in their life history. However, more research on families that have received little scientific attention and more fieldwork are needed to establish how Australian bats are Iuuctionallv adapted to the specific challenges of their local environment.