Nutrients, Antinutrients and Leaf Selection by Captive Koalas (Phascolarctos cinereus)
I. D. Hume and Carol Esson
School of Biological Sciences A08, University of Sydney, N.S.W. 2006, Australia.
The preferences of koalas for Eucalyptus foliage, as ranked by keepers at 13 wildlife parks and zoos in New South Wales, were compared with the content of a number of nutrients and antinutrients (allelochemicals) in samples of the leaves offered to koalas in each park. Statistical analyses indicated that no single factor separated the four preference groups used, but that koalas selected foliage that contained at least a minimal or threshold level of water (approximately 55%) (P=O.028) and essential oils (approximately 2% of dry matter) (P=0.044). The essential oils of the two most preferred groups had a higher proportion of volatile monoterpenes (the most aromatic oil fraction) (P<O.001) and a lower proportion of sesquiterpenes (P<O.001) than those of the two least preferred groups. The two most preferred groups also had a higher (P=0.008) ratio of nitrogen (N) to neutral-detergent fibre (NDF), and the most preferred group had the lowest (P=0.033) content of condensed tannins (CT) and the highest (P=0.010) ratio of N to CT. Thus, the ratios of N to NDF and CT are likely to be important predictors of koala acceptance of Eucalyptus foliage, and probably its nutritive value. It also appears that koalas may use eucalypt oils as a positive feeding cue, and that they prefer oils with a relatively high proportion of volatile monoterpenes.