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Dietary specialisation and Eucalyptus species preferences in Queensland koalas (Phascolarctos cinereus)

Higgins, AL, Bercovitch, FB, Tobey, JR & Hamlin Andrus, C 2011, Zoo Biology, vol. 30, no. 1, pp. 52-58.

Koalas appear to demonstrate individual dietary preferences for different species of Eucalyptus and an overall preference for particular species; however, the factors driving these preferences are not yet understood.

  Four adult male northern koalas at the San Diego Zoo were provided with nine species of Eucalyptus upon which to feed and their foraging behaviours monitored over an eight-week period. Each of the males appeared to preference the species in a different order, demonstrating individual selectivity in their choice of food. In general, however, the species most preferred by the group were E. camaldulensis and E. tereticornis. The same preferences have also been reported in other studies of Queensland koalas. The least preferred species were E. occidentalis and E. viminalis.

  Despite there being more than 600 species of Eucalyptus, koalas are known to feed on only five percent of these. Further, koalas have been observed to demonstrate individual preferences for particular Eucalyptus species. Such findings suggest that dietary preferences may be associated with intrinsic factors, such as age and reproductive state, and extrinsic factors, such as leaf chemical composition and moisture. It has been suggested that the leaf preferences of koalas may relate to age, sex, season and time of day. The influence of these factors upon dietary selection could not be examined here, however, as all subjects were adult males, the investigation occurred over only eight weeks in a single season, and observations were collected only in the morning. Furthermore, as only nine Eucalyptus species were provided, it is not known whether the species that koalas seemed to prefer in this instance would also be preferred where additional species are available.

  It has been argued that the foraging habits of koalas are more complex than they appear, and the findings of this study support this claim. While studies of the secondary plant compounds or toxic load of Eucalyptus leaves are quite common, it would be valuable to understand the other intrinsic and extrinsic factors that may affect the dietary preferences of koalas.

 

Summarised by Joanna Horsfall

 

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