It sleeps for up to 20 hours a day, gets almost all of its water from eucalyptus leaves and seeks refuge in the coolest parts of the forest. But increasingly intense heatwaves and wildfires are putting one of Australia’s most iconic species at risk.
As record-breaking temperatures continue to affect Europe, Zurich Zoo is highlighting one of the animals best adapted to extreme heat: the koala (Phascolarctos cinereus). A true specialist in conserving both energy and water, this Australian marsupial has evolved remarkable strategies to cope with the hot, dry conditions of its natural habitat. However, climate change is pushing even these extraordinary adaptations to their limits.
Sleeping up to 20 hours a day to conserve energy
Anyone observing the koalas at Zurich Zoo will almost always find them motionless among the eucalyptus branches. This is not laziness, but a highly sophisticated evolutionary strategy.
In their natural habitat—the eucalyptus forests of eastern and southern Australia—summer temperatures frequently reach 30°C (86°F). To minimise energy expenditure and reduce body heat production, koalas spend up to 20 hours a day resting.
Their activities are concentrated during the cooler hours of the morning and evening, while throughout the day they seek out the shadiest areas of the forest. Research has shown that eucalyptus forests contain microhabitats that are several degrees cooler than the surrounding environment, and koalas deliberately select these locations.
Almost all their water comes from eucalyptus leaves
In addition to being masters of energy conservation, koalas are also exceptionally efficient at managing water.
Their metabolism is among the slowest of all mammals, allowing them to reduce both their energy and water requirements. As a result, koalas are only rarely observed drinking.
Most of the water they need comes directly from eucalyptus leaves, which contain between 60 and 80 percent water. During digestion, their bodies extract this moisture, while their highly concentrated urine and extremely dry faeces further minimise water loss.
Morning dew collected on eucalyptus leaves also contributes to their water intake. Only during prolonged droughts or extreme heatwaves do koalas occasionally descend from the trees to search for water.
The young koala born at Zurich Zoo in May 2025 has now reached this stage of development as well. At around six months of age it began feeding on eucalyptus leaves, and by approximately one year old it will be fully weaned.
Climate change is testing even the koala
Despite these remarkable adaptations, temperatures above 35°C (95°F), increasingly prolonged droughts and more frequent wildfires are making it increasingly difficult for koalas to survive in the wild.
Current estimates suggest that between 400,000 and 570,000 koalas remain in their natural habitat, although in some regions recent bushfires have caused population declines of up to 50 percent.
For this reason, the species is considered threatened, making conservation efforts more important than ever.
Zurich Zoo’s role in conservation
Zurich Zoo contributes to the conservation of the species through its breeding programme, helping to maintain a reserve population outside the koala’s natural habitat.
The zoo also supports Koala Conservation Australia, an organisation that operates a specialist koala hospital, protects eucalyptus forests, conducts scientific research and runs breeding programmes aimed at the future reintroduction of koalas into the wild.
Through educational talks and public outreach activities, Zurich Zoo also uses its koalas to raise awareness about the effects of climate change and the urgent need to protect one of Australia’s most iconic animals.
