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Digestion, nutrition & metabolism

Nutrients, antinutrients and leaf selection by captive koalas (Phascolarctos cinereus)

Hume, ID, & Esson C 1993, Australian Journal of Zoology, vol. 41, pp. 379-92.

Eucalyptus foliage selection by captive koalas is driven by a suite of variables rather than a single factor.  The present study revealed that foliage most preferred by captive koalas had higher volatile monoterpenes, which are the most aromatic oil component, and lower sesquiterpenes in their essential oils.  Moreover, the most preferred foliage had higher nitrogen to fibre ratio, lower condensed tannin content and higher ratio of nitrogen to condensed tannin content than rejected foliage.

  The study was conducted in cooperation with thirteen wildlife parks and zoos in New South Wales, where samples of foliage used to feed captive koalas were analysed and the koalas’ preferences noted by their keepers.  The Eucalyptus foliage was subsequently separated into four groups based on the koalas’ perceived preferences, with Group 1 being the most preferred group and Group 4 the least preferred.  Different nutrient and antinutrient contents were analysed including water, oil, oil components, nitrogen, fibre, total phenolics and condensed tannins.  Overall, there was no distinct separation between the four preference groups indicating that leaf preferences were not determined by one or two main factors.  It was found that the ratios of nitrogen to fibre, nitrogen to condensed tannins and condensed tannin content were the factors that had the strongest influence on the koalas’ preference for Eucalyptus. The authors proposed that these factors were likely to be important predictors of the nutritive value of the foliage.  Furthermore, the authors of the study noticed the rejection of leaves that contained less water and essential oils by the koalas, suggesting that there are threshold levels of water, oil and nitrogen in the foliage to which the koalas accept.  The authors concluded that there may be two sets of factors that affect the dietary habits of the koalas; one of which determines whether the koala eats a leaf or not (based on water, oil and nitrogen content), while the other determines how much of the leaf the koala eats (based on nitrogen to fibre ratio, nitrogen to condensed tannins ratio and condensed tannin content).

  The authors of this study encouraged further research into the food preferences of free-living koalas, noting that there remains uncertainty as to whether or not these findings are applicable to free-living koalas. Similar observations have been reported, however, in koalas in the Brisbane Ranges National Park in Victoria and in greater gliders which, like koalas, are Eucalyptus specialists. 


Summarised by Cherie Chan


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