Koalas rely on trees for water: study

A new study of koalas indicates the Australian marsupial relies on trees not just for shelter, food and rest, but also for drinking water.

An analysis published on Sunday in the journal Ethology claims to have captured koala drinking behaviour in the wild for the first time, showing how the native animal can drink by licking water running down tree trunks during rain.

Led by Dr Valentina Mella from the University of Sydney's School of Life and Environmental Sciences, the study uses observations of koalas drinking collated from citizen scientists and independent ecologists between 2006 and 2019.

"For a long time, we thought koalas didn't need to drink much at all because they gained the majority of the water they need to survive in the gum leaves they feed on," Dr Mella said in a statement on Sunday.

Wild koalas consume about 510 grams of fresh eucalyptus leaves each day, with water in the foliage believed to contribute approximately 75 per cent of their water intake in both summer and winter.

"Now we have observed them licking water from tree trunks. This significantly alters our understanding of how koalas gain water in the wild. It is very exciting," Dr Mella said.

Free-ranging koalas were seen licking water running down a tree trunk during or immediately after rain a total of 44 times in the You Yangs Regional Park in Victoria, with a further two observations of drinking recorded in the Liverpool Plains in NSW.

They were observed licking the wet surfaces of branches and tree trunks during rain across a range of weather conditions, even when free-standing water was available in dams.

"This suggests koalas were drinking not as a result of heat stress and that this behaviour is likely to represent how koalas naturally access water," Dr Mella said.

Koalas drinking in this way relies on the marsupial experiencing regular rainfall to access free water, and indicates they may suffer "serious detrimental effects if lack of rain compromises their ability to access free water," Dr Mella said.

"We know koalas use trees for all their main needs, including feeding, sheltering and resting.

"This study shows that koalas rely on trees also to access free water and highlights the importance of retaining trees for the conservation of the species."

The release of the study coincides with Wild Koala Day.