The koala (Phascolarctos cinereus) is the largest arboreal folivore found in Australia, with a lifestyle adapted to life in the trees. It is the only extant member of the family Phascolarctidae but debate continues amongst researchers as to whether there are two or three subspecies, or whether there are any at all. The koala feeds almost exclusively on leaves of Eucalyptus and allied genera such as Corymbia, Angophora and Lophostemon, which are potentially harmful to some other mammals. Koalas are able to detoxify eucalyptus oil and obtain enough nutrients from the leaves to live. Their caecum (intestine) is the largest of all mammals. The caecum is a large fermentation chamber, where leaves (cellulose) are digested by micro-organisms.

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The koala’s scientific name comes from the Greek words ‘phaskolos’ meaning pouch, ‘arktos’ meaning bear, and the Latin word ‘cinereus’, which means ash-coloured. Its Australian indigenous name is koobor which means ‘does not drink water.’ Its common name ‘koala’ is an aboriginal name from the Hawkesbury River district (near Sydney).

Home range

• Varies with the quality of habitat with larger home ranges in poorer habitat.
• Ranges from less than 2 ha to 150 ha in size. In good habitat areas of South East Queensland, females have a home range of 5-8 ha and males 9-22 ha.
• Male koalas generally have a larger home range than females.
• Home ranges can overlap.

Distribution

• Fragmented distribution throughout eastern Australia.
• Found in Queensland, New South Wales, Victoria, and South Australia.
• Extends as far north as Atherton Tablelands (west of Cairns), and as far south as the islands off Victoria and South Australia.
• Introduced to some islands (Kangaroo, Phillip Islands) where populations have become over-abundant, leading to defoliation of food trees such as the manna gum — ultimately resulting in the starvation and death of koalas.
• Population in South Australia became extinct in the 1930s and since then all have been introduced from Victorian animals.
• Majority of populations in Victoria have been supplemented by translocations.

Description

Koalas have large, furry ears, a prominent black nose and a very small tail. The northern and southern populations differ in appearance.

• The southern population is heavier, with males reaching 12 kg and females 8.5 kg, while northern males reach a maximum of 8-9 kg and females 5-6 kg. They have darker fur with brown colouring, and the fur is longer and thicker; these are adaptations to the cooler climate.
• The northern population is a lighter grey colour, with more prominent light ventral colouring.

The koala is adapted for movement in the trees, with long and strong digits and claws. The koala’s hands have two ‘thumbs’, and their feet have a joined second and third digit with two claws used for grooming.

Signs

• Scats:
• Small, oval-shaped with well-digested small particles.
• Very hard and dry.
• Often in piles on the ground under Eucalypt trees or in branches.
• Small branches often cover the ground under Eucalypt trees, which indicates that koalas have been feeding in that tree.

Habitat

• Eucalyptus woodlands and forests of eastern Australia.
• Are also known to rest in non-eucalypt trees.

Ecology

Life history and behaviour

• Generally solitary.
• Mostly nocturnal (inactive for most of the day).
• Males survive for up to 10-12 years and females 12-14 in the wild but may survive for up to 24 years in captivity.

Breeding

• Mating season extends from early spring to midsummer.
• Gestation period is approximately 35 days.
• Female usually produces one young per year.
• Newborn koala is approximately 19 mm long and 5.5 gms in weight.
• Newborn climbs unaided to the pouch and attaches to a teat.
• Mother produces a special form of faeces known as ‘pap’ which inoculates the gut with bacteria required for its adult diet of Eucalyptus leaves.
• 6 months later, young emerge from pouch and has grown around 20 cm in length.
• Joey is carried on the mother’s back for a further 6 months.
• During the breeding season, males advertise by bellowing and scent marking from a gland on their chest.

Food

• Eucalyptus and allied genera leaves.
• Very selective feeders, preferring young foliage at the tips of the branches.
• Very poor source of energy which is high in toxic compounds — therefore, koalas have a very low metabolic rate.
• Consume water very rarely.
• Also known to feed on non-eucalypt species, but these contribute a very minor proportion to the diet.

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