The koala is one of Australia’s most recognizable and beloved animals, often depicted as a gentle, sleepy creature clinging to a tree. These marsupials are native to the eucalyptus forests of eastern and southern Australia. Despite their cuddly appearance, koalas are not bears, but are classified as marsupials, sharing a lineage with kangaroos and wombats. The inaccurate name “koala bear” has persisted since early European settlers first observed them, but the koala is the only living member of its family, Phascolarctidae. Their biology includes a highly specialized diet, unique physical traits, and surprising forms of communication.
Specialized Survival: The Eucalyptus Diet and Sleep
The koala’s existence is shaped by its diet of eucalyptus leaves, a food source toxic to most other mammals. Eucalyptus foliage contains chemical compounds which the koala must neutralize. To process this difficult food, they possess specialized liver enzymes and a very long digestive organ called a cecum, which can measure up to 6.5 feet (2 meters) in length.
This extended cecum contains millions of bacteria that break down the fiber and help detoxify the leaves. Because eucalyptus leaves are low in nutrition and caloric content, requiring significant energy to digest, koalas have a slow metabolic rate. They remain largely sedentary, resting or sleeping for up to 20 hours each day to conserve energy.
Koalas are selective eaters, choosing only certain leaves from a small fraction of the hundreds of eucalyptus species available. The name “koala” is thought to originate from an Aboriginal word meaning “no water,” reflecting that they rarely need to drink, as they get most of their hydration from the moisture in the leaves.
Hidden Details: Fingerprints, Pouches, and Paws
One surprising fact about the koala is a physical trait they share with humans and some primates: unique fingerprints. The intricate, swirling ridge patterns on a koala’s finger pads are so similar to human fingerprints that they are virtually indistinguishable without microscopic examination. This trait aids in grasping and climbing.
Their specialized climbing ability is enhanced by the structure of their paws. Koalas have two opposable digits, essentially two “thumbs,” on each front paw, which allows for an extremely powerful grip on branches. On their hind paws, the second and third digits are fused together, with the separate claws acting like a specialized grooming comb.
As marsupials, koalas give birth to extremely underdeveloped young called joeys, which are about the size of a jellybean at birth. The joey immediately crawls into its mother’s pouch, where it spends the first six to seven months of its life. Unlike kangaroos, the koala’s pouch opens toward the rear, a feature that protects the baby from falling out while the mother climbs. Before a joey eats eucalyptus, the mother produces a substance called “pap,” a specialized form of feces containing the necessary micro-organisms to help the baby digest the toxic leaves.
Sounds and Social Lives: Koala Communication
Koalas are largely solitary and territorial, but they communicate with a wide range of vocalizations. The most dramatic sound is the deep, guttural bellow produced by males, often described as sounding like a cross between a snore and a loud belch. This low-frequency call travels long distances through the forest, serving to attract mates and intimidate rival males.
The male koala possesses a specialized vocal organ, including a descended larynx and unique velar vocal folds, allowing them to produce sounds much lower in pitch than expected for their size. This deep basso sound exaggerates their body size, as females tend to pay more attention to the bellows of larger males. Mothers and joeys also communicate with soft clicking, squeaking, and humming sounds. All koalas share a common, panicked cry that sounds like a baby screaming when they are under stress.