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 Ta.
N. major entered into and spontaneously aroused from
torpor at Tas as low as 5C, and
became torpid at Tas as high as
23C. Like other temperate-zone Australian vespertilionid bats, some torpid
N. major maintained a relatively high
Tb at low
Ta. 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 (
Tb –
Ta) differential at low
Ta or became torpid at relatively
high Ta , conductance values
approached euthermic levels.