Koala

SPECIES Koala
TAXONOMY Phascolarctos cinereus
STATUS Vulnerable (Redlist); Vulnerable QLD (ala.org.au)

The Koala is the most recognisable Australian marsupial. They are a native species and unique to Australia. They have become a symbol for several industries to attract the world market to buy Australian made products and visit our shores. Although industry may appreciate it now, the Koala has experienced many trials since European settlement. 

History
There are three (some scientists describe two only) subspecies which are divided by geography and separated into Northern (QLD), Intermediate (NSW), and Southern (VIC and SA). The adaptations are temperature related in that cooler climate koalas have adapted with darker, longer, and more dense fur and are larger in general.  

  • Phascolarctos cinereus adustus: Northern or Queensland 

  • Phascolarctos cinereus cinereus: Intermediate or New South Wales

  • Phascolarctos cinereus victor: Southern or Victoria and South Australia

The scientific name comes from the two Greek words ‘phaskolos’ meaning pouch, and ‘arktos’ meaning bear. Often today it is referred to as a ‘koala bear’. However, it is not related in any way to the bear which is a placental omnivore mammal. When the animal was given its scientific name by Europeans, few people except Aboriginal Australians had ever seen a marsupial. At that time, the bear was the closest that they could relate it to. In reality, the Wombat is the closest living relative to the Koala. They both share vestigial tails (meaning no external tail), cheek pouches, few premolar teeth, and unique blood proteins.

Habitat
Koalas are arboreal and occur in woodlands typically dominated by eucalyptus species. They will only remain on the ground long enough to move to another tree in search of food. They are found in ‘koala populations’ where there are overlapping territories that sustain multiple individuals. In their home range koalas have shelter trees and food trees. They tend to revisit these selected trees throughout the year. 

Feeding
Koalas are a highly specialised folivore (a leaf eating herbivore) possessing unique blood proteins and an extended digestive tract. Eucalyptus leaves are very high in fibre and very low in protein. Within the caecum, a fermentation process involving millions of bacteria decompose the cellulose that make up the plant cell walls. The leaves also contain strong smelling oils and phenols poisonous to most mammals. Although these may be avoided, some leaves during certain seasons may also contain cyanide-type compounds. Koalas are able to detoxify these substances in their liver. 

  • The bacteria required for digestion is actually passed from the mother Koala and consumed by the Joey at 22 weeks through a substance called ‘pap’.

To obtain enough food, an adult koala will eat more than 500 grams (or 10% of its body weight) of leaves every day. They will consume this in short sessions of up to six per day, store food in their cheek pouches, and rest for up to 20 hours in a single day to conserve as much energy as possible. The inactivity and slow digestive tract allows them to fully extract the nutrients and moisture from the leaves. This process almost completely eliminates the need to source water, except in times of drought where the leaves do not contain enough. It is also one reason why Koalas prefer areas of higher rainfall.

  • The name ‘koala’ is an Aboriginal word meaning ‘no drink’. This is descriptive in the sense that koalas are able to obtain enough moisture from their diet of eucalyptus leaves and will rarely look for additional water sources. 

Of the 700 varieties of eucalyptus tree species, the Koala will only feed on the leaves from approximately 40 of these. With its acute sense of smell, the Koala will choose a suitable variety based on the smell of the tree trunk. They will also smell the leaves to decide whether they are safe to eat. The foliage on some species of tree can be toxic, even to the koala, during certain seasons of the year.

The main Koala forage in the southern mainland is the Manna Gum (Eucalyptus viminalis), also called White Gums or Ribbon Gums. A forest species of eucalyptus, it grows up to 50 metres in height and sheds long ribbons of bark. Similar to Candlebarks, the tree is distinguished by the juvenile leaves which occur in opposite pairs and are long, thin, glossy, and green. Manna Gums grow in areas with higher rainfall, at higher elevations, and cooler aspects.

  • Koalas enjoy the benefits of a natural insect repellent by consuming eucalyptus leaves.  

Behaviour
Koalas are generally solitary creatures, however can be found in overlapping home ranges where food sources are sufficient to sustain individuals. These populations are referred to as a ‘Koala Colony’. They are solitary in the sense that they only spend time together for mating or in a maternal relationship of caring for the young. 

They will sleep up to 22 hours per day in order to conserve energy to digest their food, becoming active during the night and when it is time to move to another tree in search of food. Climbing down from a tree in order to move to another involves climbing down backwards, bottom first. They will also take some time out for moving between branches, grooming, or social behaviour. 

They communicate with each other by scent marking and calling. Males will rub their scent gland on their trees, or urinate on the base of the tree and nearby ground. Both males and females make a variety of vocal calls such as bellows, snarls, and screams. During mating season a very distinct scream can be heard. They are most active during mating season when it is time to dominate challengers or locate females. A male koala will survive in the wild in suitable habitat for up to 10 years. A female will survive up to 15 years. 

Appearance
The Koala has soft, thick, ash-grey coloured fur. The length of fur and depth of colouring change based on geographic region. The chest is a white or cream colour. They have a round head, fluffy ears, a stout body, and are without a tail. The nose is distinctly spoon shaped and black. Males are larger and range up to 80 centimetres in length. 

Built for an arboreal lifestyle, the Koala has a wedge shaped cartilaginous plate that forms a platform to allow it to stabilise in the forks of trees. They have very long arms, powerful claws, and fingers that have been especially designed for climbing with the first and second fingers opposable to the other three. Their fur acts as insulation against temperature fluctuation. They will alter their exposure by positioning the lighter coloured chest hair to reflect heat or turning their backs towards the sun to absorb it. 

Reproduction
Koala populations are recorded as having a dominance hierarchy among the males. The dominant male has successfully obtained status through both physical and verbal expression.  Although capable of breeding from 18 months of age, young males do not reach full physical maturity until 4 to 5 years and are prevented access to the females due to this dominance. The most dominant male will mate with most of the females within the population, and will revisit them regularly while they continue to be in season. The female group is often referred to as ‘the harem’.

Australia hosts many types of natural wildlife. Of the three classifications of mammals, the more unusual species are native to this country. The Koala is a marsupial and unique to this continent. 

The three classifications of mammals are: 

  • Placental Mammals: which experience live births of fully developed offspring;

  • Monotremes: which lay eggs (there are only two species still in existence (the platypus and the echidna); and,

  • Marsupials: also known as metatherian mammals, give birth to immature young that develop further in the protection of the mother’s pouch. Some species have protective folds of skin which may be permanent or only develop at the onset of reproduction.

The Koala’s pouch is situated in the centre of the female’s abdomen with the opening facing outwards and towards the bottom. As the joey grows and puts its head out, it can appear that the pouch is facing backwards.

Breeding is both an annual and seasonal event. If conditions are favourable, females will produce a single young during the spring or summer months. Twins are relatively common. The female Koala has the sole responsibility of caring for the young.

Gestation lasts only 35 days. In the later stages of pregnancy, the opening of the pouch will constrict.

Neonates (the newly born joey) are less than 2 centimetres long and weigh less than 1 gram. At this stage it is blind, hairless, and only has buds for hind limbs. It does have functional lungs, digestion, urinary systems, muscled shoulders, and forelimbs with tiny claws. Once born, the tiny forearms and claws are used to crawl its way from the birth canal (the urogenital opening), climb up through the mother’s fur, and enter into her pouch. The neonate also has well developed lips and will seek out the smaller of the two teats and firmly attach itself and will begin to suckle. The young will remain on this same teat throughout its pouch life. The mother will contract her muscles to stop the joey from falling out of the pouch. By the time it is weaned, the teat will be elongated and far too large to accommodate the tiny mouth of the next neonate. Instead, the next born will choose the smaller teat that was unused in the previous year. The joey will remain in this position for the first 13 weeks of its life.

At 13 weeks fur will start to appear.

By 22 weeks the eyes have opened and the joey will begin to poke its head out of the pouch. This is a critical stage in the joey’s life as it stimulates the mother’s cloaca to make a modified faeces called ‘pap’. The joey will consume this substance which provides the intestinal microflora needed to digest eucalyptus leaves. It also doubles the body weight of the joey. 

At 24 weeks the joeys will have a dark brown, full coat of fur. The first teeth appear and they have their first feed of eucalyptus leaves. The joey will weigh at least 500 grams.

By 30 weeks the fur colour has lightened. It will spend much of its time clinging to the belly fur of its mother while she protects it by wrapping her arms around it.

36 weeks sees an end to the joey’s time in the pouch, becoming more and more adventurous. It will spend as much time clinging to the mother’s back as it will venturing away from her. At this stage its body weight is up to 2 kilograms. Mothers spend this time teaching their joeys how and what to eat (or what not to eat) amongst the different species of eucalyptus. 

A new pregnancy will see the end of the joey’s access to the pouch and subsequent suckling. Pregnancy induces hormonal changes that cause the mother to terminate the behaviour. Old bushmen tell stories of how they have seen mothers ‘cuff or spank’ their young when it is time for them to stop. 

52 weeks marks the anniversary where the mother will likely have a new neonate to tend, fully breaking the bond with the mature joey. The joey may be independent physically, but it still needs its mother around. 

During the next 6 to 12 months the young will continue to live in close proximity of their mother, often in the same tree.

  • Female koalas are sexually mature from the age of 2 to 2 ½ years. Females will often remain near or within the home range of their mother.

  • Male koalas, although capable of breeding at 18 months, likely will not have the opportunity due to a dominant male and will become nomadic while they seek to establish their own home range.

Threats
From early settlement through the 1920s, millions of Koalas were slaughtered for their thick, soft fur. Statistics evidence that in 1924, two million koala pelts were exported from the eastern ports in Victoria, New South Wales, and Brisbane. Although they were declared as Protected in the late 1920s in NSW, exports continued until the end of that decade from QLD. It is generally said that this high commercial harvesting had no long term impact on the overall population.

Since that time, Koala distribution has reduced from habitat disturbance through land clearing, drought, changing fire patterns, and changes to fire management. When population densities increase, the defoliation of preferred tree species can lead to the crash of isolated populations. Vulnerability to predation and vehicular strike also increases as Koalas are forced to move on the ground to find new areas.

The devastation to habitat by the fires that occurred in January of 2020 has had a direct impact on koala populations due to the intensity and widespread area. Many koalas were caught in the canopy and could not escape, resulting in death or severe injury. Among the injured, many are in remote locations and will not be rescued. With the canopy lost and any water source contaminated, they may fall prey to opportunistic and feral predators.

Koala suffer from the communicable disease Chlamydia pneumoniae. It is widespread among many populations and affects the animal through keratoconjunctivitis that leads to blindness, urinary tract infections that lead to chronic wetness, and reproductive tract infections that lead to reduced fertility. Even if isolated and treated, the organism is not fully eliminated. This is spread through the dominant males, however isolated populations do exist that are free of this disease. 

More recently, a serious and untreatable virus has been identified as the Koala Retrovirus (KoRV) and also known as Koala Immune Deficiency Syndrome (KIDS). This is associated with immune changes, ill thrift, and disease presence in the host animal. It is occurring more in the northern populations, and is similar to that seen in humans as HIV/AIDS. It too, is questioned as communicable which means that it is transferred by direct contact. 

Updated 5 May 2021