Koalas drink water by licking wet trees, scientists discover

Enigmatic marsupial has previously been thought to absorb almost all its moisture from eating leaves

Koalas drink water by licking moisture that is running down trees, scientists have discovered, a finding they say “significantly alters” our understanding of the much-loved but enigmatic animal.

It had been thought the tree-dwelling marsupial absorbed most of its fluids from chomping on juicy leaves in Australia’s eucalyptus forests.

But researchers from the University of Sydney have now documented koalas’ drinking behaviour in the wild for the first time. In a study published in the journal Ecology, they describe how the marsupials slurp up water running down smooth tree trunks during rain.

“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,” said Valentina Mella, a postdoctoral research associate at the university’s School of Life and Environmental Sciences.

“But 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.”

Australia is currently enduring its longest dry period ever documented, with little rainfall and record maximum temperatures.

That has prompted koalas – which usually spent most of their time in the safety of the treetops – to climb down in search of water.

The animals suffer severe heat-stress and mass deaths during prolonged hot and dry conditions, and Australian conservationists have set up artificial drinking stations to help them stay hydrated.

The Sydney ecologists say their research could help determine where and when such resources are needed, as well as reinforcing how vital trees are to the koalas’ survival.

“This type of drinking behaviour – licking tree trunks – relies on koalas being able to experience regular rainfall to access free water and indicates that 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.”

Wild koalas eat around 510g of succulent eucalyptus leaves each day, and the moisture in the foliage they feed on is believed to contribute about three quarters of their water intake.

Koalas have been observed to drink water in captivity, but this behaviour is considered unusual and often put down to disease or severe heat stress.

There are also anecdotal reports of koalas in the wild drinking from waterholes in summer when temperatures exceed 40C, and they have been observed approaching humans to access water during droughts and after fires.

But the koalas documented licking trees did so during a range of weather and even when free-standing water was available nearby.

“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,” said Dr Mella.

The study collated 46 observations supplied by members of the public and independent ecologists in Victoria state’s You Yangs Regional Park and the Liverpool Plains in New South Wales between 2006 and 2019.

“Our observations probably only represent a minority of the drinking that normally takes place in trees during rainfall,” said Dr Mella.

She added: “As koalas are nocturnal animals and observation of their behaviour rarely occurs during heavy rainfall, it is likely that their drinking behaviour has gone largely unnoticed and has therefore been underestimated in the past.”