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Koalas can predict hot days and adjust their body temperature

For the first time, scientists have observed wild koalas regulating their body temperatures ahead of hot summer days by lowering their temperatures during cooler mornings. 

The research, led by Valentina Mella from the University of Sydney, revealed that koalas can predict extreme heat and adjust their body temperatures accordingly. 

Koalas prepare for a warming climate

Over a two-week study in 2019, koalas displayed the highest and lowest body temperatures ever recorded for the species. This self-regulation helps koalas save water by reducing the need for evaporative cooling.

“This self-regulation requires individual koalas to predict days of extreme temperature from overnight and early morning conditions, adjusting their body heat regulation accordingly,” Mella said. 

The research showed that koalas’ core temperatures fluctuate with environmental conditions, which is an adaptive tactic to reduce water usage by 18 percent. This behavior might be more crucial for surviving hot days than previously known tactics like tree-hugging.

Koalas self-regulate their body temperature 

Koalas generally maintain a core body temperature of 36.3 degrees Celsius, but on hot days, they start with a lower body temperature, allowing it to rise with the air temperature. This approach is less reliant on water for cooling down. 

However, as climate change causes temperatures to increase, this strategy could become risky since temperatures above 40 degrees Celsius can be fatal for leaf-eating mammals like koalas.

Koalas use various methods to manage their body temperature, including their insulative fur, concentrated urine production to conserve water, and a low metabolism to reduce heat production. They also pant, lick their fur for evaporative cooling, seek cooler microhabitats, and adopt tree-hugging postures. 

Previous work by the research team also recorded koalas drinking freely available water on hot days, a behavior that was previously unknown.

Temperature regulation as a survival technique 

The study was conducted near Gunnedah in New South Wales, an area with an older population of koalas suffering from chlamydial disease. Remarkably, all of the koalas were still alive six months later, indicating that this temperature modulation is a survival technique. 

“Global climate models forecast that dry, hot weather will escalate and drought events will increase in frequency, duration and severity. This is likely to push koalas and other tree-dwelling leaf-eating mammals towards their thermal limit,” said Mella.

“Our results reinforce the importance of climate mitigations for ensuring future survival of koalas.”

More about the survival techniques of koalas

Koalas have developed several survival techniques to navigate the challenges of their environment. 

Specialized diet 

One of the most notable is their specialized diet, which consists almost exclusively of eucalyptus leaves. 

These leaves are tough, fibrous, and low in nutrition, but koalas have a highly specialized digestive system with a long gut to extract the maximum amount of nutrients. Their slow metabolic rate helps conserve energy, allowing them to survive on this limited diet.

Behavioral strategies 

In terms of behavior, koalas spend most of their time in trees, which provides safety from ground-based predators. 

They are mostly nocturnal or crepuscular, being active during the cooler parts of the day and night, which helps them avoid the midday heat and conserve water. 

During extreme heat, koalas can often be found hugging the cooler, lower parts of trees or spreading out their limbs to release body heat.


Additionally, koalas communicate with each other using a range of vocalizations. This helps them establish and maintain territories, find mates, and warn off rivals without needing to expend energy on physical confrontations. 

Impact of climate change on koalas

Koalas are significantly impacted by climate change, which exacerbates the challenges they face from habitat destruction and disease.

Rising temperatures and altered weather patterns can lead to more frequent and intense heatwaves, exacerbating dehydration and heat stress in koalas. 

Diminishing food sources 

Additionally, climate change affects the quality of their primary food source, eucalyptus leaves. These trees are sensitive to changes in climate.

Altered rainfall patterns and increased carbon dioxide levels can reduce the nutritional content of the leaves and make them more toxic, which can diminish koala food sources and affect their health.

Habitat loss

Climate change contributes to more severe and frequent bushfires, which can devastate koala habitats, causing loss of food sources and direct harm to the koala population. These fires not only destroy the trees koalas depend on but can also result in significant mortality for the species. 

The overall impact of climate change threatens the survival and conservation of koalas, making it crucial to address these environmental changes to help preserve this iconic Australian species.

The study is published in the journal Conservation Physiology.


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