Production of Milk and Nutrition of the Dependent Young of Free-Ranging Koalas (Phascolarctos cinereus)
Andrew K. Krockenberger1,*, Ian D. Hume1, Steven J. Cork2
1School of Biological Sciences, University of Sydney, Sydney, New South Wales 2006, Australia;
2Commonwealth Scientific and Industrial Research Organization, Division of Wildlife and Ecology, Lyneham, Australian Capital Territory 2062, Australia
The production of milk by lactating females, and energy expenditure and foliage intake of their dependent young, were investigated in free-ranging koalas. Koalas had the lowest mass-specific daily milk-energy production at peak lactation so far recorded in a mammal, but the duraction of reproduction was 58% longer than the combined marsupial and eutherian average. As a consequence, the total energy input to reproduction in koalas was similar to that in other mammals. We propose that the prolonged lactation and low daily rate of energy transfer to the young be female koalas is an adaptation to the low energy availability from their diet of Eucalyptus foliage. Energy requirements (field metabolic rates) of young koalas were lower than those expected for typical marsupials (only 60% at permanent pouch exit), which may be a necessary preadaptation that allows the low rate of maternal energy transfer. However, the energy requirements of the adult females were no lower than expected for marsupials. This pattern of energy requirements and age resulted in a linear relationship between field metabolic rate and mass for the koalas in this population. Differences in milk production between the years of the study coincided with fluctuations in the availbilityof preferred young foliage, which suggests that the lactational output of koalas may be flexible and affected by diet quality. Despite the interannual differences in milk production, growth of the young was similar in the two years.