Koala Profile 

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42. Koala Profile

Common Name: Koala
Scientific Name: Phascolarctos cinereus
Genus: Phascolarctos
Family: Phascolarctidae
Order: Diprotodontia
Class: Mammalia
Phylum: Chordata
Conservation Status: Vulnerable (IUCN)

Physical Description

Koalas are iconic Australian marsupials known for their stout, tailless bodies, large heads with fluffy ears, and spoon-shaped noses. They have soft, thick, grey to brown fur that provides insulation and comfort while they spend long hours resting in trees. Koalas have sharp claws that help them grip and climb eucalyptus trees.

• Length: 60 – 85 cm

• Weight: 4 – 15 kg (males are typically larger than females)

Koalas have opposable thumbs on their hands and feet, which help them grasp tree branches, and their strong limbs allow them to cling to trees for hours, making them excellent climbers despite their sleepy nature.

Koalas are native to eastern Australia and live in a variety of forested environments, particularly those that are home to eucalyptus trees, which are crucial to their survival. These habitats include Eucalyptus woodlands, open forests, and coastal forests.

Diet

Koalas are herbivores and have a highly specialized diet consisting almost exclusively of eucalyptus leaves. Eucalyptus leaves are tough, fibrous, and low in nutrients, so koalas have evolved a slow metabolism to digest this food.

• Diet: Mainly eucalyptus leaves (up to 1 kilogram per day)

• Water intake: Koalas rarely drink water, getting most of their moisture from the leaves they eat, though they may drink from water sources during extreme droughts like they did during the destructive bushfires of 2019.

To break down the toxins found in eucalyptus leaves, koalas have a specialized digestive system with a long cecum that helps ferment the leaves.

Behavior and Social Structure

Koalas are solitary animals and have a reputation for being quite lazy, spending up to 20 hours a day sleeping. Their slow metabolism and energy-poor diet contribute to this behavior. However, during the few hours they are active, they move between trees, feed, or interact with other koalas.

Koalas are territorial, and males especially maintain overlapping territories that they mark with scent glands located on their chests. During the breeding season, males produce loud bellows to attract females and signal their presence to other males.

Fun Fact: Koalas’ unique vocalizations can be heard from over a kilometer away!

Reproduction

Koalas are marsupials, meaning their young, called joeys, are born underdeveloped and complete their development in their mother’s pouch.

• Breeding season: Spring to summer (October to February)

• Gestation period: About 35 days

• Litter size: Usually 1 joey

• Weaning: 6 – 7 months (joey stays with the mother for about 12 months)

When a joey is born, it’s only the size of a jellybean. It crawls into its mother’s pouch, where it continues to develop, feeding on milk. After a few months, the joey will begin to peek out of the pouch and start eating "pap," a nutrient-rich, partially digested form of eucalyptus that the mother produces to help the joey transition to solid food.

Did You Know?

• Unique Fingerprints: Koalas have fingerprints that are remarkably similar to humans! In fact, they’re so similar that koala fingerprints could be confused with human prints at crime scenes.

• Low Energy Lifestyle: Due to their low-nutrient diet, koalas spend most of their time resting to conserve energy. They’re perfectly adapted to their sleepy lifestyle!

• Picky Eaters: Out of over 600 species of eucalyptus trees, koalas prefer only a handful of species, making their habitat preferences quite specific.

• Unique Name: ''Koala'' means ''No drink'' in Aboriginal language, which clearly represents their lack of drinking. They get most of their water and other nutritions through the Eucalyptus leaves they eat.

Role in the Ecosystem

The Koala is a specialist folivore — a leaf-eater — and its ecological role in the eucalypt forests and woodlands of eastern Australia is more significant and multifaceted than its sedentary, slow-moving lifestyle might suggest. As a selective browser of eucalyptus foliage, the Koala exerts consistent and targeted grazing pressure on the canopy of preferred tree species, promoting new growth by stimulating the production of fresh leaf shoots and influencing the competitive dynamics between different eucalypt species in the forests it inhabits. 

The leaf litter generated by its feeding activity — dropped foliage, chewed fragments, and dislodged bark — contributes to the organic matter of the forest floor, supporting invertebrate communities and the decomposer networks that underpin forest soil health. Koala dung is a particularly important ecological contribution — the gut microbiome of the Koala, which enables it to detoxify the potent chemical defenses of eucalyptus leaves that are lethal to most other mammals, produces feces rich in partially processed plant compounds and microbial biomass that fertilize the forest floor and may play a role in inoculating juvenile Koalas with the gut bacteria they need to begin processing eucalyptus leaves — a process called pap feeding in which mothers pass specialized feces to their joeys as a critical dietary supplement during weaning. 

As prey, Koalas are taken by dingoes, powerful owls, wedge-tailed eagles, and large pythons, connecting the forest canopy to higher trophic levels in the eastern Australian food web. Their use of specific tree hollows and forked branch junctions for resting creates physical disturbances in the canopy that benefit other species, and the scratching of their strongly clawed feet on bark surfaces may contribute to bark structural diversity in heavily used trees. 

As a culturally iconic and charismatic species, the Koala also serves as a powerful umbrella species for the conservation of the eucalypt woodland and forest ecosystems it inhabits — landscapes that support an extraordinary diversity of other species whose conservation is advanced by the political and public attention directed at the Koala.

Why They're At Risk

Vulnerable (IUCN Red List) | Endangered (Australian law)

The Koala faces a multitude of threats. It was listed as Endangered under Australia's Environment Protection and Biodiversity Conservation Act in 2022 — an upgrade from Vulnerable that reflected accelerating population declines driven by a convergence of threats that have intensified dramatically in recent decades. Habitat loss and fragmentation remain the foundational threat. The clearing of eucalypt woodland and forest for agriculture, urban development, and infrastructure across Queensland, New South Wales, Victoria, and South Australia has eliminated vast areas of Koala habitat and reduced the remaining forest to increasingly isolated and degraded patches. 

The catastrophic 2019–2020 "Black Summer" bushfires burned through approximately 24% of the koala's core habitat range in a single season — killing an estimated 60,000 koalas directly and destroying the food trees on which survivors depend across enormous areas, in a scale and intensity of fire that is directly linked to the drying and warming of southeastern Australia under climate change. Chlamydia — a bacterial infection caused by two Chlamydia species specific to Koalas — is endemic across much of the Koala population and causes blindness, reproductive tract disease, and death across wild populations, reducing fertility and survival in ways that make recovery from other threats slower and more difficult. However, a vaccine for this disease has been approved back in 2025 (after over 10 years of development by the University of Sunshine Coast).

Vehicle strikes and dog attacks are significant ongoing causes of mortality, particularly in urbanized landscapes where Koalas must cross roads and gardens to move between increasingly fragmented tree stands. Drought — increasing in frequency and severity under climate change — reduces the water content and nutritional quality of eucalyptus leaves, forcing Koalas to descend to the ground more frequently in search of water and alternative food sources, where they are more exposed to vehicle strikes, dog attacks, and human disturbance.

Climate change also directly affects eucalyptus leaf chemistry — elevated atmospheric CO₂ is documented to increase the ratio of indigestible fiber to protein in eucalyptus leaves, reducing their nutritional value and potentially affecting the ability of Koalas to meet their energetic requirements on the same quantity of foliage. Inbreeding in isolated habitat patches reduces genetic diversity and immune function, making fragmented populations less resilient to disease and environmental stress.

The combination of habitat destruction, disease, climate change, and demographic fragmentation creates a set of interacting threats that no single conservation intervention can address — effective Koala conservation requires simultaneous action on land clearing laws, habitat corridor restoration, disease management, climate policy, and urban planning across the entirety of the species' eastern Australian range.