Koalas refined taste in leaves follows unusual start

Monday 1 May, 2023
The May Catchment Critter of the Month is the Koala (Phascolarctos cinereus) as part of the Goulburn Broken Catchment Management Authority’s (CMA) Grey Box Grassy Woodlands community wildlife awareness campaign. This project is supported by the Goulburn Broken CMA through funding from the Australian Government’s National Landcare Program.

 Goulburn Broken CMA Project Officer, Janice Mentiplay-Smith, said the Koala weighed up to 15 kilograms and was the largest tree-dwelling marsupial in the Goulburn Broken catchment.

“The Koala is mostly active at night and only comes down to ground level to move between trees. Access to water is not necessary as the Koala receives all its moisture from the leaves it eats,” Ms Mentiplay-Smith said.

“These days it’s hard to believe the Koala population was once severely reduced for the fur trade, with Australia’s Marsupial Destruction Act in 1877 openly sanctioning their slaughter. During the life of the fur trade the total number of Koala skins exported to Europe exceeded many millions.

“While no longer threatened by the fur industry the Koala still walks a precarious line of survival. In February 2022, the Koala was officially listed as endangered in the Australian Capital Territory, New South Wales and Queensland. It’s not classified in Victoria. Despite its legal protection, a large proportion of the Koala’s habitat and food source occurs on private land which is largely unprotected.”

The Koala is solitary and territorial with each individual requiring around 100 trees for its nutritional needs. A Koala’s diet depends on where it lives. Of Australia’s 700 or so eucalyptus species, only some are palatable to the Koala and make up its staple diet.

“The Koala is a very particular diner, it selects only the choicest leaves from a tree – preferably new, soft and juicy growth - before moving on to the next, meaning large tracts of habitat is required,” Ms Mentiplay-Smith said.

“Eucalyptus leaves are toxic, tough and difficult to digest. To manage this the Koala has evolved a slow metabolism and long digestive system to break down the leaves. However even this effort yields just 25 per cent of the nutrients ingested and requires the Koala to sleep around 20 hours a day. The other four hours are spent eating up to one kilogram of eucalyptus leaves each night.”

Koalas are seasonal breeders, mating in spring through to early autumn. After 35 days gestation a jellybean-sized joey weighing 0.5 grams is born (twins occur occasionally). The joey crawls into its mother’s pouch and attaches to one of two teats where it grows and develops. It stays in the pouch for 13 weeks, opens its eyes at around 22 weeks and at around seven months of age it will climb aboard its mothers’ back. By its first birthday, the joey is independent. 

Ms Mentiplay-Smith said however, there was something the joey needed to do first.

“Before it can eat toxic eucalyptus leaves, it must ‘inoculate’ its digestive system with its mother’s intestinal microorganisms by ingesting ‘pap’, a specialised form of her dung. This enables the joey to process and digest the only food in the world a Koala can eat,” she said.

“Whilst this may seem fairly gross to us, it is known as coprophagy, and it is a necessary survival tactic that quite a few mammals around the world use.”

Read more about the Koala and the 29 other mammal species present in the Goulburn Broken catchment’s Grey Box Grassy Woodlands environments in “the Mammal Book’, a 58-page booklet featuring beautiful photographs and informative text. To view a copy, visit the website The Mammal Book - GB CMA - Goulburn Broken CMA

The Koala is the Goulburn Broken Catchment Management Authority’s catchment critter of the month. Photo S Drysdale.

The Goulburn Broken CMA acknowledges and respects First Nations people and the deep connection they have with their land and waters.

We acknowledge the Yorta Yorta and Taungurung people and their ancestors/forbears as Traditional Owners of the land and waters in the Goulburn Broken Catchment (and beyond). We value our ongoing partnerships with Yorta Yorta Nation Aboriginal Corporation and Taungurung Land and Waters Council for the health of Country and its people.

We pay our respects to Elders past, present and emerging and acknowledge and recognise the primacy of Traditional Owners obligations, rights and responsibilities to use and care for their traditional lands and waters.

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