Dk. Coburn et F. Geiser, SEASONAL-CHANGES IN ENERGETICS AND TORPOR PATTERNS IN THE SUBTROPICALBLOSSOM-BAT SYCONYCTERIS-AUSTRALIS (MEGACHIROPTERA), Oecologia, 113(4), 1998, pp. 467-473
Little is known about how animals from tropical and subtropical climat
es adjust their energy expenditure to cope with seasonal changes of cl
imate and food availability. To provide such information, we studied t
he thermal physiology, torpor patterns and energetics of the nocturnal
blossom-bat (Syconycteris australis 18 g) from a subtropical habitat
in both summer and winter. In both seasons, S. australis frequently en
tered daily torpor at ambient temperatures between 12 and 25 degrees C
when food and water were withheld. Unlike patterns observed in temper
ate animals, mean minimum metabolic rates during torpor were lower in
summer (0.47 +/- 0.07 ml O-2 g(-1) h(-1)) than in winter (0.75 +/- 0.1
1 ml O-2 g(-1) h(-1)). Body temperatures during torpor were regulated
at 19.3 +/- 1.0 degrees C in summer and at 23.4 +/- 2.0 degrees C in w
inter. Torpor bout duration was significantly longer in summer (7.3 +/
- 0.6 h) than in winter (5.5 +/- 0.3 h), but in both seasons, bout dur
ation was not affected by ambient temperature. Consequently, average d
aily metabolic rates were also significantly lower in summer than in w
inter. Body temperatures and metabolic rates in normothermic bats did
not change with season. Our findings on seasonal changes of torpor in
this bat from the subtropics are opposite to those made for many speci
es from cold climates which generally show deeper and longer torpor in
winter and are often entirely homeothermic in summer. More pronounced
torpor in subtropical S. australis in summer may be due to low or unp
redictable nectar availability, short nights which limit the time avai
lable for foraging, and long days without access to food. Thus, the re
versed seasonal response of this subtropical bat in comparison to temp
erate species may be an appropriate response to ecological constraints
.