Study solves longtime mystery of how a koala gets its drinking water


Scientists have solved a mystery about koala behaviour: how these tree-dwelling* marsupials* drink enough water to live.

A new study describes koala drinking behaviour in the wild for the first time, finding that they lick water running down the smooth surface of tree trunks during rainfall — called stemflow — and do not only rely on the water content of the leaves that make up their diet.

The findings, which the researchers said could help in koala conservation* efforts, were based on 46 observations of koalas in the wild from 2006 to 2019, mostly at You Yangs Regional Park, west of Melbourne, Victoria.

One of the wild koalas the scientists watched licking a smooth tree trunk during rain. Picture: AAP/The University of Sydney

“I think the main message is that behavioural* observations in the wild are very important to establish what is normal and what is unusual, and to truly understand what animals need. If we watch them carefully, they will tell us,” said University of Sydney ethologist* Valentina Mella, lead author of the research published last week in the journal Ethology.

Koalas spend most of their lives high up in eucalyptus trees. They rely on a diet of eucalyptus leaves, normally eating around 500g to 800g daily.

Because koalas are nocturnal, it’s difficult to observe them drinking in this way. Picture: AAP/The University of Sydney

The word koala is thought to have come from the indigenous Dharug people’s word meaning “no water”.

The question of whether or how they drink water has long puzzled people.

“Koalas have been alleged* to never drink free water in the wild, or to drink only occasionally. Drinking behaviour has often been considered unusual and attributed to* disease or to severe heat stress,” Mella said.

koala drink

A koala in Belair National Park, SA, drinks rain off the road as desperately needed rain falls in South Australia in January. Picture: Brad Fleet

“Koalas were thought to gain the majority of the water that they require from the moisture content in the leaves that they feed on and to drink water unintentionally* in the wild by eating wet leaves after rain, or when dew is present on the leaf surface,” Mella added.

They sleep about 20 hours a day to conserve* energy because the leaves they eat require a lot of energy to digest.

“Koalas are nocturnal animals, so they are only active at night, and they are arboreal, which means that they live in trees and rely on them for food, shelter and, as we just discovered, also for drinking,” Mella said.

“Koalas actually spend 98 per cent of their lives in trees and the only time they are on the ground is when they are trying to find another tree with a more generous food supply or a mate.”


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