Introduction

The Koala Study Program at the University of Queensland has developed a unique method of determining the diet of koalas by examining leaf-cuticle remains found in faecal pellets collected from free ranging koalas. The use of this method has facilitated a better understanding of the way koalas utilise the variety of tree species found in their habitat.
Controlled feeding experiments have validated this method for captive koalas. The use of this technique has revealed that day-time tree occupancy cannot be used to predict the diet of free-ranging koalas.
 

Method

Making reference slides

Leaves from each species of Eucalyptus, and other trees, used by koalas in the studied areas are treated so that the cuticle, showing an imprint of the epidermal cell layer with stomatal structures, can be mounted on a microscope slide, stained and viewed using a microscope. A photograph of one slide of each species is taken to compile a reference collection of roost and diet species. This reference collection and the key developed from it by Nyo Tun (1993) has been expanded to encompass most Eucalyptus species found on our study-sites, including the Blair Athol Coal Mine at Clermont.
 Different species of Eucalyptus show significant differences in stomatal size and density as well as in shape, size and density of epidermal cells.

A reference slide showing the epidermal cell layer of E. baileyana at x40 magnification
 
 
 

A reference slide showing the epidermal cell layer of E. signata at x40 magnification
 

 Making slides from faecal pellets

Fresh pellets found under trees where koalas have been located are collected, crushed, bleached and mounted in a similar manner to the reference slides. In the prepared faecal, slide fragments of leaf cuticle are found and determined to species using the reference slides and the key.
 

 Validation of technique

To test the validity of this method a controlled feeding experiment was implemented on four captive koalas (two males and two females) held at the University of Queensland’s Veterinary Farm at Pinjarra Hills.
 

 The koalas were fed according to the following regime:
* Week 1: Diet composed of a mixture of Eucalyptus species excluding  E. tereticornis
* Week 2 This week the koalas received only E. tereticornis
* Week 3 Two koalas received a diet of only E. propinqua whilst the remaining two were given only E. microcorys
* Week 4 All four koalas were fed controlled proportions of E. tereticornis, E. resinifera and E. macculata

Pellets were collected hourly between 6 am and 9 am and between 4 pm and 8 pm. One pellet was chosen from each day of weeks 2, 3 and 4, prepared and analysed by the method developed by The Koala Study Program.

Results

From these results it is evident that the appearance of species in faecal pellets can be used to determine diet components for koalas. Leaf material is retained in the gut of the koala for 34 to 154 hours before appearing in the faeces.