Aj. Munn et Tj. Dawson, Thermoregulation in juvenile red kangaroos (Macropus rufus) after pouch exit: higher metabolism and evaporative water requirements, PHYSIOL B Z, 74(6), 2001, pp. 917-927
The population dynamics of red kangaroos (Macropus rufus) in the Australian
arid zone is tightly linked with environmental factors, which partly opera
te via the survival of juvenile animals. A crucial stage is the young-at-fo
ot (YAF) stage when kangaroos permanently exit the pouch. We have examined
the thermal biology of YAF red kangaroos during ages from permanent pouch e
xit until weaning. Over a wide range of environmental temperatures (ambient
temperature [T-a] -5 degrees to 45 degreesC), YAF red kangaroos had a mass
-specific metabolism that was generally twice that of adults, considerably
higher than would be expected for an adult marsupial of their body size. Th
e total energy requirements of YAF red kangaroos were 60%-70% of those of a
dult females, which were three times their size. Over the same range in T-a
, YAF red kangaroos also had total evaporative water losses equal to those
of adult females. At the highest Ta (45 degreesC), differences were noted i
n patterns of dry heat loss (dry conductance) between YAF red kangaroos and
adult females, which may partially explain the relatively high levels of e
vaporative cooling by YAF. By weaning age, young kangaroos showed little ch
ange in their basal energy and water requirements (at T-a 25 degreesC) but
did show reduced mass-specific costs in terms of energy and water use at ex
tremes of T-a (-5 degrees and 45 degreesC, respectively). In their arid env
ironment, typified by unpredictable rainfall and extremes of T-a, young red
kangaroos may need to remain close to water points, which, in turn, may re
strict their ability to find the high-quality forage needed to meet their h
igh energy demands.