First study to show koalas drink water by licking tree trunks

Koalas are one of the world’s most charismatic animals. But there is a lot westill don’t know about them. For example, how do the marsupials access waterin the treetops? Do they only absorb moisture from the gum leaves they eat? Ordo they come down from the trees to drink from a waterhole? Until now, no onereally knew.

A study published today in Ethology , led by a researcher from TheUniversity of Sydney, has captured koala drinking behaviour in the wild forthe first time. The paper describes how koalas drink by licking water runningdown smooth tree trunks during rain.

The news arrives in time to celebrate Wild Koala Day on Sunday 3 May.

“For a long time, we thought koalas didn’t need to drink much at all becausethey gained the majority of the water they need to survive in the gum leavesthey feed on,” said Dr Valentina Mella , in the School of Life andEnvironmental Sciences. “But now we have observed them licking water fromtree trunks. This significantly alters our understanding of how koalas gainwater in the wild. It is very exciting.”


Australia is currently suffering the longest dry period ever documented, withsevere rainfall deficits and record maximum temperatures. Koalas experiencesevere heat-stress and mass mortality events in prolonged hot and dryconditions and they spend more time drinking from artificial water stations ifrain is scarce.

Further research could investigate when and why koalas from different areasneed access to free water – not contained in the leaves as moisture butavailable freely as liquid, such as rain, river water or puddles – and whetherwater supplementation is necessary for some populations.

“This type of drinking behaviour – licking tree trunks – relies on koalasbeing able to experience regular rainfall to access free water and indicatesthat they may suffer serious detrimental effects if lack of rain compromisestheir 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 toaccess free water and highlights the importance of retaining trees for theconservation of the species.”

Koalas rarely drink water

Each day, wild koalas eat around 510 grams of fresh succulent eucalyptusleaves, and the water in the foliage they feed on is believed to contributeabout three quarters of their water intake in both summer and winter.

Among their adaptations to the Australian climate, koalas also possessextraordinary urinary concentrating abilities and have restricted respiratoryand cutaneous water loss compared to similar-sized mammals.

In captivity, koalas have been observed to drink water, but this behaviour hasoften been considered unusual and attributed to disease or to severe heatstress.
However, anecdotal reports suggest that koalas in the wild drink fromwaterholes in summer when temperatures exceed 40 degrees Celsius.

Koalas have also been observed approaching humans to access free water (inbottles, gardens and swimming pools during drought and after fire. But this isconsidered an unusual occurrence.

Observing licking behaviour

For this study, Dr Mella collated observations of koalas drinking in the wildmade by citizen scientists and independent ecologists between 2006 and 2019 atthe You Yangs Regional Park in Victoria and the Liverpool Plains in NSW. Eachobservation was koala behaviour noticed by chance and reported to Dr Mella.

There were 44 observations of free ranging koalas licking water running down atree trunk during or immediately after rain in the You Yangs Regional Park.

The other two observations of koala drinking behaviour were recorded betweenthe towns of Gunnedah and Mullaley, in the Liverpool Plains. One was an adultfemale, with a joey, who drank profusely and uninterruptedly for 15 minutes.The other was an adult male who drank at a steady pace for 34 minutes.

“As koalas are nocturnal animals and observation of their behaviour rarelyoccurs during heavy rainfall, it is likely that their drinking behaviour hasgone largely unnoticed and has therefore been underestimated in the past,” DrMella said. “Our observations probably only represent a minority of thedrinking that normally takes place in trees during rainfall.”

Koalas were observed accessing water in trees by licking the wet surfaces ofbranches 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 thatthis behaviour is likely to represent how koalas naturally access water,” saidDr Mella.

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