Koala

Quick Take

• A baby koala's very first solid meal is something most people would find deeply unsettling, yet this disturbing food source is the key to their survival. Discover the unusual first meal →
• Koalas share a physical feature with humans that shows up in forensic science, and it has nothing to do with their face. Explore their unique anatomy →
• Their famously lazy lifestyle isn't laziness at all. It's the result of a hidden biological trade-off that quietly cost them a vital organ's full potential. See the energy trade-off →
• Despite being one of Australia's most iconic animals, koalas nearly vanished in a single decade, and the trigger was not what most people assume. Uncover the near-extinction trigger →

The koala is one of the most loved mammals in the world with its adorable round face, unique nose, and gentle demeanor. The name “koala” actually comes from the language of the Aborigines and is believed to mean “no drink.” Ironically, koalas don’t need to consume as much water as most animals because the eucalyptus leaves they eat hydrate them naturally.

Evolution

Scientists claim that koalas evolved over tens of millions of years in forests on the Australian continent, which were thicker and wetter than today’s forests. Their chewing apparatus evolved as the forests became drier and full of leaves and plants that were tougher to chew. It’s thought that the bite force of the koala adapted to this challenge, allowing the koala to shred tough eucalyptus leaves.

Classification

The Koala is a small to medium-sized mammal that is found inhabiting various types of forests in south-eastern Australia. Despite its appearance and the fact that it is also known as the Koala Bear, Koalas are in fact marsupials but are so distinctive among marsupials that they are classified in a scientific group of their own.

Although they are now considered to be one of Australia’s most iconic mammal species, when European settlers first arrived things were very different, with millions of Koalas known to have been killed every year for their pelts (fur). The Koala is a unique animal that famously feeds only on the leaves of the eucalyptus trees which they inhabit. However, this diet is very hard to digest and lacks many of the vital nutrients that are key to the survival of most animal species. Today, the Koala is affected by habitat loss as vast areas of land are cleared every year to support growing development.

Types of Koalas

There are three distinct types of koalas based on the region of Australia they inhabit and the color of their fur:

• Brown Koala: Native to the Victorian Region of Australia. Other names: Victorian koala and Southern koala.  Brown koalas have the thickest coats of the species to keep them warm in a cooler climate. They’re also the largest type of koala. There are up to 28,000 Brown koalas in Victoria and 19,000 in Southern Australia.
• Gray Koala: Native to Queensland, Australia, the Gray koalas have thin gray fur and are the smallest type. Other names: Northern koala and Queensland koala. This type is the most threatened.
• Gray-Brown Koala: Native to New South Wales, Australia. These koalas have gray-brown fur and face extinction, with only 16,000 left in the wild. Other names: koalas of New South Wales, Grayish-Brown koalas.

Anatomy and Appearance

The Koala is one of the most charismatic of all marsupials, with its large, wide face and round, white-tufted ears giving it the appearance of a small bear, along with its lack of a visible tail and smooth, black nose. The Koala has dense and soft grey or grey-brown fur which is lighter on its underside and mottled on the rear. Because Koalas spend almost all of their lives in the trees, they have evolved several adaptations to help them with their arboreal lifestyle, including having short, powerful limbs tipped with sharp claws.

Having two opposable thumbs and three fingers on each hand means that Koalas can grip even the smoothest of bark when climbing and feeding in the trees. Koalas also have human-like fingerprints.

Koalas move about in the trees by jumping, first gripping the trunk with their front paws (helped by their rough paw pads and claws) before then moving both their back legs up the tree together, allowing them to get higher up.

Distribution and Habitat

The Koala would have once been widespread throughout south-eastern Australia and on a number of its surrounding islands, but populations (particularly in the south) were wiped out in some areas due to hunting. They are, however, surprisingly resilient and adaptable animals that are known to inhabit various types of forest from the tall eucalyptus forests to coastal regions and even low-lying woodlands further inland.

Even though they are common in much of their natural range today, land clearance has not only meant a loss of their habitats but also separated populations from one another, making them more and more isolated. it is not just the loss of habitat to human activity, though, that has led to population declines in certain areas, as quick-spreading forest fires can devastate vast areas of land in minutes and severely affect the local Koala populations in the process.

Behavior and Lifestyle

The Koala is a solitary and nocturnal animal that spends most of the daytime hours sleeping in the fork of a eucalyptus tree. Their low-energy diet (which is comprised only of the fibrous leaves of the eucalyptus) results in Koalas leading a largely inactive lifestyle, as they can spend up to 18 hours a day sleeping or simply sitting in the trees to conserve energy. Everything from sleeping to eating and even breeding is done in the trees, as although Koalas are known to come down to the ground quite frequently, it is only so they can move to another tree.

Koalas are also sedentary, meaning they occupy a fixed home range that can vary in size depending on the abundance of food available (home ranges are smaller in areas with more food as there is no need to travel as far). Although the home ranges of males and females do overlap, males will not tolerate rival males intruding on their territory and will fight viciously by scratching and biting.

Reproduction and Life Cycles

During the breeding season, males can be heard producing loud booming calls through the forest, used both to attract a female mate and to deter potential rivals. In Koala society, it is the dominant male that gets to mate with the most females, meaning that although males (like females) can reproduce from the age of two, breeding is not normally successful until the male Koala is between 4 and 5 years old and has established his dominance.

After a gestation period that lasts for a mere 35 days, a single joey is born about the size of a jellybean and very underdeveloped, immediately crawling unaided into the pouch on its mother’s belly. Here it attaches itself to one of the two teats and remains in the safety of the pouch until it is weaned at between 6 and 7 months old after having grown dramatically. The young Koala then clings onto its mother’s back, where it tends to remain for another few months or until the next season’s young have developed and are ready to leave the pouch.

Diet and Prey

The Koala is a herbivorous animal that only feeds on the leaves of the eucalyptus (gum) tree in order to survive. Despite there being more than 700 different species of eucalyptus, Koalas only seem to feed on 30 of them, depending on the surrounding habitat. Eucalyptus leaves are tough and fibrous and often toxic, making them inedible to other herbivorous animals, but the koala has evolved to fill this gap in the ecosystem, with large cheek pouches where the leaves are stored.

Once full, the Koala then begins to grind the leaves down into a pulp using their flat cheek teeth, with some of the toxins then being detoxified by the liver. The Koala also has an incredibly long digestive tract (more than three times its body length) to help it to break down the tough leaves. To help the process, Koalas are also known to occasionally eat soil, bark, and gravel to aid the digestion of such a fibrous plant.

Predators and Threats

Despite being relatively small, the lack of native mammalian predators in Australia means that adult Koalas have very few natural predators except large birds of prey. Young Koalas are more vulnerable, however, and are preyed on by several different animals including snakes, but both are most threatened by domestic animals,, particularly dogs, that not only attack Koalas but are also known to spread disease into local populations. This is one of the biggest threats to koalas in certain areas, as large numbers have been affected, particularly by the Chlamydia bacterium. Although antibiotics can treat it, they also destroy the gut bacteria koalas need to digest eucalyptus leaves, making treatment difficult and sometimes fatal.

Other threats to the current Koala populations include habitat loss due to growing human settlements, tourist developments, and forest fires that can spread rapidly in semiarid regions. The Koala populations on several islands have also been affected by overpopulation, as the increasing number of individuals means that there is less food to go around.

Interesting Facts and Features

Due to the fact that Koalas sustain themselves on a diet that is only comprised of leaves, they have little need to drink as they get almost all of the water that they need through their food. However, living on a diet so low in nutrients has led the koala to evolve a very small brain relative to its body size, as a larger brain would drain the body’s limited energy supplies.

After having spent their first six months of life developing in their mother’s pouch, suckling milk, baby Koalas must then attempt to eat solid foods, the first being their mother’s soft droppings. Young Koalas are thought to do this as it contains microbes that help the young both fight off disease and begin digesting the tough, fibrous leaves of the eucalyptus.

Relationship with Humans

The Koala would have once been abundant throughout the forests of south-eastern Australia, but intense hunting for their soft fur in the early 20th century led to drastic population declines and even local extinction in some areas. When the industry peaked in 1924, two million pelts were traded, which eventually led to public outcry over the situation. Since then, the hunting of Koalas has been banned, and management of populations has seen them increase once again.

Despite their rising population numbers, though, Koalas are affected by Human activity throughout much of their natural range, mainly in the form of habitat loss as vast areas of land are cleared annually for development and agriculture. However, the koala today is one of Australia’s most famous and treasured mammal species and is found on numerous emblems and in stories not just in Australia but worldwide.

Conservation Status and Life Today

Today, the Koala is listed by the IUCN as Vulnerable in the wild, though in 2022 Australia’s federal government uplisted koalas to Endangered under national law in Queensland, New South Wales, and the Australian Capital Territory. In the recent past, population numbers were stable and widespread; in fact too high in some areas, with 10,000 individuals relocated back to mainland Australia over the past 75 years to prevent island populations from growing out of control. Populations are, however, becoming more and more remote and isolated from one another due to habitat loss, bushfires, road accidents, and domestic dog attacks. In fact, a report published in December 2020 estimated that the 2019–2020 bushfires impacted around 61,000 koalas, through death, injury, or habitat loss. The Australian Koala Foundation now estimates there are fewer than 57,920 Koalas left in the wild, maybe as few as 32,065.

Some koalas have also been exposed to diseases in certain areas. Where possible, though, infected Koalas (and particularly those that have been attacked by domestic dogs) are given veterinary first aid to help them recover and prevent outbreaks from spreading through entire populations.