Thermal Biology and Metabolism of the Greater Long-eared Bat, Nyctophilus major (Chiroptera :Vespertilionidae)

Abstract

Nyctophilus major is the largest member of its Australian-centred genus. Flow-through respirometry was used to investigate the thermal and metabolic physiology of adult N. major from south-western Australia. Oxygen consumption, carbon dioxide production, respiratory quotient, evaporative water loss and thermal conductance were measured at ambient temperatures of 5–40C. N. major was thermally labile and could be euthermic or torpid at low T_a. N. major entered into and spontaneously aroused from torpor at T_as as low as 5C, and became torpid at T_as as high as 23C. Like other temperate-zone Australian vespertilionid bats, some torpid N. major maintained a relatively high T_b at low T_a. Body mass and the duration of captivity had no detectable effect on the thermal responses of bats. The basal metabolic rate (BMR) of N. major was 85% of predicted, and falls within the the range of mass-specific BMRs reported for vespertilionid bats. While mean torpid á VO₂ was reasonably high, torpor still facilitates substantial metabolic savings. However, because of the high á VO₂ , N. major may not be able to remain torpid for more than about 60 days, relying solely on fat reserves. The evaporative water loss (EWL) of euthermic and torpid N. major was also high, although EWL during torpor was reduced compared with euthermy. Wet conductance was lower than predicted and probably relates to the solitary, tree-roosting habits of N. major. As has been reported for other bats, conductance values during torpor were lower than those during euthermy, but when torpid bats maintained a large ( T_b – T_a) differential at low T_a or became torpid at relatively high T_a , conductance values approached euthermic levels.