Koala (Phascolarctos cinereus) is a herbivorous, marsupial mammal species that is endemic to Australia. Living a tree-dependent life in eucalyptus forests, this animal typically weighs between 5 and 12 kilograms and exhibits pronounced sexual dimorphism depending on gender. Its strong claws and opposable digits allow it to grip branches firmly.
Koala (AA)
Morphological Characteristics
Koalas are marsupials distinguished by their large heads, short necks, and thick, soft fur. Their body length varies by sex and geographic location. In southern populations, males can reach an average length of 78 cm and a body weight of 11.8 kg, while females average 72 cm in length and weigh approximately 7.9 kg. Northern populations are smaller in size, with males weighing around 6.5 kg and females approximately 5.1 kg.
Males have broader faces, smaller ears, and a prominent sternal gland on the chest. Females possess a backward-facing pouch that opens upward. The tail is vestigial. Fur color is generally grey or brown, with white coloration on the chin, chest, and inner forelimbs. The ears are fringed with long white hairs, and white spots may be present on the rump.
Koalas have large, strong claws. On the forelimbs, the first and second digits are opposable to the remaining three, allowing for a strong grip on branches. On the hind limbs, the first digit is short and broad, while the second and third digits are partially fused yet have separate claws. These adaptations demonstrate the koala's specialization for an arboreal lifestyle.
Distribution and Habitat
Koalas (Phascolarctos cinereus) are endemic to Australia and are naturally distributed along the eastern coastline, from northeastern Queensland to Victoria and parts of South Australia. Historically widespread across eastern and southeastern eucalyptus forests, their range has contracted due to habitat loss. Today, natural populations are found in Queensland, New South Wales, and Victoria, while populations in South Australia, around Adelaide and the Murray River, as well as Kangaroo, French, Phillip, and Magnetic Islands, have been established through human intervention.
Koalas inhabit forests and forest edges dominated by eucalyptus trees, typically at elevations below 600 meters. Adapted entirely to an arboreal existence, they spend nearly their entire lives in eucalyptus canopies, which provide food, shelter from predators, resting sites, and places for rearing young. Koalas depend on dense, humid, evergreen eucalyptus forests, which are classified as “forest” in terrestrial biome classifications.
Behavior and Ecology
Due to their diet of eucalyptus leaves, which are low in nutrients and rich in cellulose, koalas have evolved an energy-conserving lifestyle. They spend between 18 and 22 hours per day sleeping or remaining inactive. They are mostly nocturnal, with peak activity occurring at night.
Koalas are solitary animals, with each individual maintaining a defined home range. The size of these territories varies by sex and age. Males typically have larger ranges than females, and these areas may partially overlap with those of other individuals.
Feeding
Koalas are highly specialized herbivores that feed almost exclusively on the leaves of eucalyptus trees (Eucalyptus spp.). These leaves contain toxic compounds, are high in fiber, and low in protein, making them indigestible for most animals. However, koalas have adapted to this diet through evolutionary modifications, particularly in their digestive system. Their large and complex cecum enables the fermentation and breakdown of fibrous plant material to extract nutrients.
Koalas consume up to 500 grams of eucalyptus leaves per day, depending on geographic location, season, and body size. Since they obtain most of their water from the moisture in the leaves, they rarely need to drink in natural conditions. Nevertheless, because the chemical composition of eucalyptus leaves varies throughout the year, koalas exhibit selective feeding behavior, choosing among different eucalyptus species to balance toxicity and optimize nutrient intake.
Feeding Koala (Pixabay)
Reproduction
Koalas are gonochoric, meaning they are a sexually dimorphic species, with sexual maturity typically occurring around the age of two in females and around four years in males. Although male koalas are biologically capable of reproduction at the age of two, they usually mate later due to the need for sufficient size and dominance to access females. Females mate only once a year, with the breeding season occurring during the summer months, particularly in December and January.
Koalas exhibit a polygynous mating system; males mark their territories and use vocalizations to gain access to females. Females have an estrous cycle lasting approximately 27–30 days. The gestation period is relatively short, averaging around 31 days. At birth, the joey is extremely small (approximately 0.5 grams) and underdeveloped; however, it climbs unaided into the mother’s pouch, where it attaches to a teat and remains for about 5–7 months. During this period, it feeds exclusively on the mother’s milk.
After leaving the pouch, the young koala is carried on its mother's back and typically becomes independent around the 11th month. Nevertheless, even after gaining independence, it continues to live near the mother for some time. In the wild, koalas have an average lifespan of 13–17 years, while in captivity, they can live for approximately 15–20 years.
Koala Joey (AA)
Conservation Status and Threats
The koala (Phascolarctos cinereus) was classified as “Vulnerable” by the International Union for Conservation of Nature (IUCN) in 2020. This assessment is based on various scientific studies indicating an average population decline of approximately 28% over the past three generations (about 18–24 years). This decline is particularly pronounced in inland regions most affected by drought; for example, localized declines of up to 80% have been reported in parts of inland Queensland.
The primary threats facing koalas include habitat loss and fragmentation, drought and rising temperatures linked to climate change, vehicle collisions, dog attacks, and infectious diseases—particularly Chlamydia spp. infections. Additionally, low genetic diversity in certain populations renders these groups more vulnerable to environmental changes and disease outbreaks. Urban expansion and agricultural activities contribute to the destruction of eucalyptus forests, eliminating critical sources of food and shelter for koalas.
