Possibly a lot more than we thought.
This article is suited to students in all years studying Biological or Earth and Space sciences. Although younger students may not be able to read the entire article or answer all questions, extracts should be taken by the teacher and adapted to suit learners to provide context and relevance to the learning. It is well suited to students learning about the needs and features of living things, alongside their dependence on their habitat.
Try the included investigation with students in the garden or school grounds.
Word Count / Video Length: 453 / 0:30 minutes
This is a video of a koala licking rainwater from a tree. Not the most exciting viewing, perhaps, even for hardcore koala fans, but it has made scientists sit up and take notice.
That’s because (a) it hasn’t really been noticed before, let alone filmed and (b) it’s not the kind of thing koalas were thought to do.
The reason for (a) is largely that people don’t go koala spotting at night in the rain. The reason for (b) is largely the animal’s well-understood diet.
“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,” says Valentina Mella from the University of Sydney, Australia, the lead author of a paper in the journal Ethology.
Koalas in the wild eat around half a kilogram of fresh eucalyptus leaves each day and the water in the foliage is believed to contribute about three-quarters of their water intake in both summer and winter.
They also have extraordinary urinary concentrating abilities, Mella says, and have restricted respiratory and cutaneous water loss compared to mammals of a similar size.
Koalas have been seen drinking water in captivity, and wild koalas will approach humans and accept water during drought or after fire, but such behaviour has been considered unusual and attributed to disease or severe stress.
Similarly, Mella says, there are anecdotal reports that koalas in the wild drink from waterholes in summer when temperatures exceed 40 degrees Celsius.
However, there has not been a solid body of evidence to suggest this may actually be a common and thus important thing.
For their study, Mella and colleagues collated chance observations of koalas drinking in the wild by citizen scientists and independent ecologists between 2006 and 2019 at the You Yangs Regional Park in Victoria and the Liverpool Plains in NSW.
There were 46 sightings in all of koalas licking water running down a tree trunk during or immediately after rain. One adult kept it up at a steady pace for 34 minutes. And that’s just the tip of the iceberg, Mella suggests, because of (a) above.
Importantly, koalas were seen licking trees even when free-standing water was available in dams, suggesting it is natural behaviour and may be an important way to get the water they need – which makes Australia’s current drought more than a little problematic.
“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,” Mella says.
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