Island Koalas: Eating Habits

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Blue gum (eucalyptus) leaf under microscope

Blue gum (eucalyptus) leaf under microscope

Whether it is in the koala barn at the San Diego Zoo or in the field in Australia, the fine details of the lives of koalas provide a steady stream of questions for keepers and researchers alike.

I have just returned from Brampton Island, which is a small island near our main research site, St. Bees Island (see post, Koalas: Floating Research Station). Both islands lie several miles off the coast of Queensland, and both are home to healthy populations of koalas. However, that’s where the similarities seem to end.

Brampton Island has a diverse array of vegetation, from native pine stands through ironbark forests to wetter rain forests. By comparison, we are used to tracking koalas across the open blue gum woodlands on St. Bees Island, with occasional forays into rain forest gullies or across acacia and grass patches. It has become clear to us that the koalas living on Brampton Island encounter a more varied habitat than do the koalas that live on St. Bees.

At the San Diego Zoo, the dietary preferences of koalas have been studied so that the koalas can be fed with the species they prefer. To do this, research coordinator Jen Tobey and the keepers spent many hours offering the koalas a variety of leaves and analyzing the responses. In the wild, working out what koalas eat is a little harder, because they feed mostly at night, and then during the following day they don’t always sit in the trees where they ate. Fortunately we are able to tell what koalas have been eating by examining koala poop. The small particles of leaf left behind in their droppings present unique signatures of each species eaten, so, with a little help from some stain and a microscope, we can see what they’ve been eating.

Since the tree species are quite different between St. Bees Island and Brampton Island, we figured that their diet might be different as well. So we collected lots of leaves on Brampton (we already had a lot from St. Bees), took them back to the laboratory, and are comparing them using a microscope to the leaf fragments found in the koala poop. Now it’s just a question of time and a lot of slides, and we will know just how different the eating habits are of koalas on the two islands, as well as among koalas living on the same island.

Bill Ellis is the Clark Endowed Postdoctoral Research Fellow at the San Diego Zoo’s Institute for Conservation Research. Read his previous blog, Koala Conference Washed Out.