|
Energy expenditure during homeothermy
and heterothermy in the western pipstrelle, Pipistrellus hesperus
(adapted from Altringham, 1996).
|
For
hibernators like the red bat (Lausiurus borealis),its heart rate
ranges from 10-16 beats/min. (Davis, 1966);
the big brown bat (Eptesicus fuscus), 42-62 beats/min (Altringham,
1996). In contrast, the average heart rate for a bat at rest is 250-450
beats per minute and 800 beats /min during flight (Studier
et al., 1969). During hibernation, the rate of breathing declines
and becomes irregular: 60-90 minutes may pass without the bat taking a
breath. In fact, the oxygen consumption of a little brown bat (Myotis
lucifugus) hibernating at 2ºC is 140 times slower than a fully
homeothermic bat (Thomas
et al., 1990). As these numbers indicate, if a bat remains in torpor
throughout the cold season its energy savings are tremendous. However,
bats can and do arouse spontaneously, independent of ambient temperature,
causing heart rate and body temperature to change (graph).
Arousal occurs for a variety of reasons but
at a great energetic cost (Davis, 1970). |
Physiology
ofTorpor
II