Koalas, Phascolarctos cinereus, are arboreal herbivorous marsupials native to Australia. They are easily identifiable due to their stout, tailless body and large head with round, fluffy ears and a large, spoon-shaped nose.
The term koala bear is actually a misnomer. Koalas are not part of the bear family, Ursidae, but rather are a type of marsupial, which is a category of mammals most commonly associated with Australia. Marsupials are distinct from other mammals in that they give birth to their young at a relatively undeveloped stage. The young, often called joeys, then continue developing outside the womb in a pouch on the mother’s body.
In the case of koalas, joeys spend about six to seven months in their mother’s pouch before venturing out. Even after leaving the pouch, they continue to cling to their mother’s back or belly until they are about a year old.
Koalas are indeed the only existing members of the family Phascolarctidae. They’re an essential part of Australia’s biodiversity and hold significant cultural value in many Aboriginal Australian communities.
Koalas have a very unique diet. Their primary food source is eucalyptus leaves, but they are quite picky eaters. Of the approximately 700 eucalyptus species that exist, koalas will only eat from about 30 of them, with a preference for certain types varying from region to region.
Eucalyptus leaves are high in fiber and water content but low in protein, and they contain compounds that are toxic to many species. To process this diet, koalas have evolved a special digestive system with a long cecum, which allows them to break down the tough leaves and extract the maximum amount of nutrients. They also have a specialized liver that can break down the toxic compounds in eucalyptus oil.
Because the nutritional content of their food is so low, koalas must conserve energy, which leads them to sleep or rest for up to 20 hours a day. Their slow metabolic rate also helps them to survive on such a nutrient-poor diet.
It’s worth noting that despite the eucalyptus leaves’ high water content, koalas can become dehydrated during periods of high heat or drought. In such conditions, they have been known to drink from bodies of water, although this is generally unusual behavior.
Amazingly, the fingerprints of koalas are virtually indistinguishable from those of humans, even under a microscope. This is a rare example of convergent evolution.
Human and koala fingerprints are so alike in their pattern, shape, and size that even under detailed scrutiny of a microscope, they can be very difficult to tell apart. Both have a series of whirls and ridges that make up individual patterns.
This is an example of what scientists call convergent evolution, where unrelated species develop similar traits or characteristics independently of each other, typically because they’ve adapted to similar environments or ways of life. In this case, both humans and koalas have evolved to have highly sensitive fingertips likely due to an arboreal lifestyle where precise grip and tactile exploration are advantageous.
It’s worth mentioning that it’s quite unusual for marsupials to have fingerprints. Other than koalas, some primates and one type of aquatic mammal, the North American manatee, are the only other animals known to have fingerprints.
Female koalas, like all marsupials, have a pouch where the joey, the term for a baby koala, continues to develop after birth. The pouch serves as a safe, protected environment where the joey can nurse, grow, and develop until it’s ready to face the outside world.
One fascinating aspect of the koala’s pouch is that it opens toward the bottom instead of the top, which is unique among marsupials. This can seem counterintuitive as one might assume the baby would fall out. However, the pouch is designed to close tightly with a strong sphincter muscle at the opening, which holds the joey securely inside.
The baby koala, or joey, is extremely small when it’s born, about the size of a jelly bean. It crawls into its mother’s pouch immediately after birth, where it will latch onto a teat and continue its development, drinking its mother’s milk. After about six months, the joey begins to emerge from the pouch and starts eating partially digested eucalyptus leaves, called pap, which is prepared in the mother’s cecum.
The joey will continue to live in its mother’s pouch for up to a year, gradually venturing out more and more as it grows larger and stronger. By the time it permanently leaves the pouch, the joey is usually fully weaned and able to consume eucalyptus leaves on its own.
Koalas obtain most of their hydration needs from the eucalyptus leaves they eat, which are about 50% water. This unique ability allows them to live high up in the trees without having to descend frequently to drink, keeping them relatively safe from predators on the ground.
The name koala comes from the language of the Dharug people, indigenous to the Sydney area, and is often translated as meaning no water or no drink.
However, koalas will drink water if necessary, such as during times of drought or extreme heat when their hydration needs can’t be met by eucalyptus leaves alone. During these periods, they may be observed descending from their trees to drink from streams, puddles, or even from a kind person’s water bottle.
It’s worth noting that changing climate patterns and the increasing frequency and intensity of heatwaves and droughts present significant challenges for koala populations. Their reliance on eucalyptus leaves for both food and water means that changes to these trees’ health and availability due to climate change can severely impact koalas.
Despite their cute and cuddly appearance, koalas produce a very distinct and surprisingly loud vocalization, especially during the breeding season. This is primarily done by males, who emit a deep, resonant bellow as a mating call to attract females and also to warn off rival males. This bellow is quite remarkable and has often been described as a mix of snoring and belching or even the sound of a frog.
The sound is so deep and powerful that you might expect it to come from a much larger animal. The secret behind this bellow lies in the koala’s unique vocal anatomy. They have an extra pair of vocal folds outside their larynx, towards the base of the tongue, which are called velar vocal folds. These are different from the vocal cords found in most other mammals, and they enable koalas to produce their distinctive low-pitched sound.
The female koala also has a range of sounds, including snarls, screams, and wails, which can be quite loud and fierce, especially when rejecting the advances of a male or communicating distress. The young joeys make a different sound, a quieter squawk when communicating with their mother.
As of my knowledge cutoff in September 2021, the International Union for Conservation of Nature lists the koala as a Vulnerable species. This status means that the species faces a high risk of extinction in the wild unless the circumstances threatening its survival and reproduction improve.
Habitat destruction is one of the most pressing threats to koalas. Urban expansion and agricultural development are fragmenting and reducing their habitats, which primarily consist of eucalyptus forests and woodlands. This habitat loss not only reduces the available food sources for koalas but also forces them to descend from the safety of the trees more frequently, which increases their risk of being hit by vehicles or attacked by dogs.
Climate change poses another significant threat, as rising temperatures, droughts, and changing weather patterns can negatively affect the health of eucalyptus trees and the availability of suitable koala habitats. Additionally, increased frequency and intensity of bushfires can rapidly destroy large areas of koala habitat and kill or injure many individuals.
Koalas also face threats from diseases, particularly chlamydia, which can cause blindness, infertility, and death. Other health issues affecting koalas include a retrovirus similar to HIV in humans and various types of cancers.
Conservation efforts are ongoing to try to protect and rehabilitate koala populations. These efforts include habitat protection and restoration, roadkill mitigation strategies, research into vaccines for diseases like chlamydia, and the care and rehabilitation of injured or orphaned koalas.
Koalas have an unusually long digestive system for their size, primarily due to an extensive hindgut and a particularly large caecum. This adaptation allows them to break down the tough, fibrous content of eucalyptus leaves and also helps detoxify the various harmful chemical compounds they contain.
Eucalyptus leaves are notoriously difficult to digest. They’re high in fiber and low in nutrition, and they contain toxins that can be harmful or fatal to most species. However, koalas have evolved to not only survive on this diet but also to thrive on it.
Once a koala eats eucalyptus leaves, the food moves through the koala’s digestive tract to the caecum. The caecum is essentially a long, blind sac where the majority of fermentation of the fibrous material takes place. It is populated by a host of bacteria and other microorganisms that help break down the fiber into substances the koala can absorb.
The koala’s caecum is incredibly long up to 2 meters which allows the slow process of breaking down the fiber and toxins to occur. This means that food can stay in the koala’s digestive system for up to 100 hours, which is one of the longest digestion periods of any mammal. The result is that koalas extract the maximum amount of nutrients from their diet while also handling the toxic compounds effectively.
While this adaptation allows koalas to consume a food source that few other animals can, it also limits them to a very specialized diet and makes them particularly vulnerable to changes in the health and availability of eucalyptus trees.
Koalas have a very small brain, which takes up only 2% of their body weight.
One of the distinctive features of a koala’s brain is its lack of complexity in terms of folding. Most advanced mammals, including humans, have brains with a lot of folds, or convolutions, on the surface. These folds increase the surface area of the brain, which allows for more cerebral cortex cells, or gray matter. This is often associated with higher intelligence or more advanced cognitive processing.
However, the koala’s brain is relatively smooth more like the brains of less evolved animals. This could be due, in part, to their diet of eucalyptus leaves, which are low in nutritional value. The brain is a highly energy-demanding organ, and the low-energy diet of the koala might not support a larger or more complex brain. On the other hand, a simpler brain uses less energy, which fits with the koala’s slow-paced, energy-conserving lifestyle.
Despite their relatively small and smooth brains, koalas are perfectly adapted to their lifestyle and environment, demonstrating that every species evolves the characteristics that are most beneficial for its own unique way of life.
Koalas do have a highly developed sense of smell which is essential for their survival. Even though their diet consists almost entirely of eucalyptus leaves, they are very selective about the leaves they eat. They use their keen sense of smell to discern the freshness of the leaves, their water content, and even to distinguish between the different species of eucalyptus trees, preferring some species over others.
Their noses are also crucial for communication. Koalas are relatively solitary animals, but they use scent markings to communicate with each other, especially during the breeding season. Males, in particular, have a scent gland on their chest that they use to mark trees and signal their presence to females and other males.
In addition, their acute sense of smell helps them to detect predators or other potential dangers. Although they have relatively poor eyesight and rely less on their hearing than some other animals, their strong sense of smell helps them navigate their environment and stay safe.
