About Koalas

Phascolarctos cinereus
koala
Contents

What is a Koala?
Habitat & Diet
Physiology
Climbing Trees
Breeding
Communication
Threats
Save the Koala Day
Koala & Wildlife Links
Bibliography
Koala Photo Gallery

koala


What is a koala?

The koala is a small bear-like, tree-dwelling, herbivorous marsupial which averages about 9kg (20lb) in weight. Its fur is thick and usually ash grey with a tinge of brown in places.

The koala gets its name from an ancient Aboriginal word meaning "no drink" because it receives over 90% of its hydration from the Eucalyptus leaves (also known as gum leaves) it eats, and only drinks when ill or times when there is not enough moisture in the leaves. ie during droughts etc.

The koala is the only mammal, other than the Greater Glider and Ringtail Possum, which can survive on a diet of eucalyptus leaves.

Habitat & Diet

'Habitat' refers to the types of bushland that koalas like to live in. They are found in a range of habitats, from coastal islands and tall eucalypt forests to low woodlands inland.

Koalas today are found in Queensland , New South Wales , Victoria and South Australia . Their range extends from the Atherton Tableland west of Cairns in Qld to islands off the coast of Victoria and South Australia in the south, and west to central and western Qld, NSW and Victoria.

Koalas live in societies, just like humans, so they need to be able to come into contact with other koalas. It is because of this they need to have areas of suitable eucalypt forest which are large enough to support a healthy koala population and to allow for expansion by maturing young koalas. Koalas are highly territorial and in stable breeding groups, individual members of koala society maintain their own "home range" areas.

A ‘home range’ consists of a number of ‘home range trees’ and ‘food trees’ which comprise the long-term territory of the individual koala. These trees provide the koala with food, shelter and places for social contact which will support it for the term of its natural life (assuming there is no habitat clearing).

A home range varies in size depending on the habitat quality of bushland. Habitat quality can be measured in terms of the density of key food trees. "Home range trees" define the boundaries of the individual koala’s home range and can be likened to surveyors pegs marking the extent of a property. They are not always apparent to the human eye, but koalas can tell whether a tree ‘belongs’ to another koala or not. Within a socially stable group, the home ranges of individual koalas overlap with those of their neighbours. It is in the shared, overlapping trees that the majority of social interaction takes place. These are very important trees.

Koala populations only occur if suitable habitat is available and because Koala's are very fussy eaters and have strong preferences for different types of gumleaves, then the most important factor which make habitats suitable are the presence of tree species preferred by koalas (usually eucalypts, but also some non-eucalypts) growing in particular associations on suitable soils with adequate rainfall.

Research has shown that socially stable koala populations occur only when there are favourite tree species present. Even if a selection of tree species known to be used by koalas occurs within an area, the koala population will not use it unless one or two favourite species are available.

In Australia there are over 600 types of eucalypts, but koalas will only eat 40-50 varieties with only about 10 being preferred. Within a particular area, as few as one, and generally no more than two or three species of eucalypt will be regularly browsed while a variety of other species, including some non-eucalypts, appear to be browsed occasionally or used for just sitting or sleeping in.

Different species of eucalypts grow in different parts of Australia, so a koala in Victoria would have a very different diet from one in Queensland. Koalas like a change, too, and sometimes they will eat from other trees such as wattle or tea tree.

Eucalyptus leaves are very fibrous and low in nutrition, and to most animals are extremely poisonous. To cope with such a diet, nature has equipped koalas with specialised adaptations. A very slow metabolic rate allows koalas to retain food within their digestive system for a relatively long period of time, maximising the amount of energy able to be extracted. At the same time, this slow metabolic rate minimises energy requirements and they will sleep for up to 18 hours per day in order to conserve energy.

Each koala eats approximately 200 to 500 grams of leaves per day. The teeth are adapted to deal with for this. The sharp front incisors nip the leaves from the branches and the molars(back teeth) are shaped to allow the koala to cut and shear the leaves rather than just crush them. A gap between the incisors and the molars, called a 'diastema', allows the tongue to move the mass of leaves around the mouth efficiently.

Physiology

The Koala is well suited to life in the trees. The koala has an excellent sense of balance and its body is lean and muscular and its quite long, strong limbs support its weight when climbing. The arms and legs are nearly equal in length and the koala's climbing strength comes from the thigh muscle joining the shin much lower than in other animals.

Its paws are especially adapted for gripping and climbing with rough pads on the palms and soles helping it to grip tree trunks and branches. Both front and hind paws have long sharp claws and each paw has five digits. On the front paw, two fingers are opposed to the other three, rather like a human's thumb, so they are able to be moved in opposition to the fingers. This allows the koala to grip more securely. On the hind paw, there is no claw on the big toe, and the second and third toes are fused together to form a 'grooming claw'.

Koalas have a thick woolly fur which protects them from both high and low temperatures.It also acts like a 'raincoat' to repel moisture when it rains. The fur varies in colour from light grey to brown, with patches of white on the chest and neck, inside arms and legs and inside the ears. Mature males are recognisable by the brown 'scent gland' in the centre of their white chest.

The fur on the koala's bottom is densely packed to provide a 'cushion' for the hard branches it sits on, and has a 'speckled' appearance which makes koalas hard to spot from the ground.

An adult male koala can weigh between 8 and 14 kilograms and a female between 6 and 11 kilograms, with the heavier animals coming from the southern areas where they have adapted to the colder climate by an increase in body weight and thicker fur. If you see Koalas in Queensland, they look noticably smaller than Koalas from Victoria.

Koalas are mostly nocturnal animals and they are most active during the night and at dawn and dusk. This is because in the cooler hours they are less likely to lose precious moisture and energy than they would during the hotter daylight hours. An average of eighteen to twenty hours each day are spent resting and sleeping, and the remainder for feeding, moving around, grooming and social interaction.

The Koala's nose is one of its most important features, and it has a very highly developed sense of smell. This is necessary to differentiate between types of gum leaves and to detect whether the leaves are poisonous or not.

The Koala's digestive system is especially adapted to detoxify the poisonous chemicals in the leaves. The toxins are thought to be produced by the gum trees as a protection against leaf-eating animals like insects. Trees which grow on less fertile soils seem to have more toxins than those growing on good soils. This could be one reason why koalas will eat only certain types of eucalypts, and why they will sometimes even avoid them when they are growing on certain soils.

Climbing trees

When approaching a tree to climb, koalas spring from the ground and catch their front claws in the bark, then bound upwards. Claw marks are usually visible on the trunks of trees regularly used as home trees by koalas.

In the safety of their home trees, koalas assume a wide variety of sitting and sleeping postures, and they will move around the tree during the day and night to catch the sun or the breezes. On hot days it is common to see them with limbs dangling in an effort to keep cool, and during colder times, curled up in a ball to conserve body heat.

When descending a tree, koalas come down bottom first. They regularly descend to the ground to change trees, and it is there that they are most vulnerable to predators such as dogs, foxes and dingoes, and also to the risk of injury or death from cars. They walk with an awkward-looking gait and can also run. Koalas have sometimes been observed swimming, but this is not a regular occurrence.

Communication

Koalas use a range of sounds to communicate with one another over relatively large distances.

There is a deep grunting bellow which the male uses to signify its social and physical position. Males save fighting energy by bellowing their dominance and they also bellow to allow other animals to accurately locate the position of the caller.

Females do not bellow as often as males, but their calls too are used to express aggression as well as being part of sexual behaviour, often giving the impression of fighting.

Mothers and babies make soft clicking, squeaking sounds and gentle humming or murmuring sounds to one another, as well as gentle grunts to signal displeasure or annoyance.

All koalas share one common call which is elicited by fear. It is a sickening cry like a baby screaming and is made by animals under stress. It is often accompanied by shaking.

Koalas also communicate by marking their trees with their scent.

Breeding

The main characteristics of marsupials which differentiate them from other mammals is that they give birth to immature young which then develop further in a pouch. The word 'marsupial' comes from the Latin word marsupium, meaning 'pouch.' Most, but not all marsupials have a pouch in which to raise their young.

The breeding season for koalas runs roughly from September to March. This is a time of increased activity, and sound levels increase as males bellow more frequently. This is also when the young from the previous year are weaning from their mothers.

Females generally start breeding at about three or four years of age and usually produce only one offspring each year. However, not all females in a wild population will breed each year. Some produce offspring only every two or three years, depending on factors such as the age of the female and the quality of its habitat. In the average female's life span of about twelve years, this means that one female may produce only 5 or 6 offspring over her lifetime.

Once a female has conceived, it is only 34-36 days before the birth of the new baby, called a "joey". The tiny baby which is roughly 2 centimetres long and weighs less than 1 gram, looks rather like a pink jellybean as it is totally hairless, blind and has no ears.

The joey makes its way from the birth canal to the pouch completely unaided, relying on its already well-developed senses of smell and touch, strong forelimbs and claws and an amazing sense of direction. Once inside the safety of the pouch, it attaches itself to one of the two teats, which swells to fill its mouth. This prevents the joey from being dislodged from its source of food. The mother contracts her strong sphincter muscle at the pouch opening to prevent the baby from falling out.

The young koala drinks only mother's milk for the first six to seven months and remains in the pouch for that time, slowly growing and developing eyes, ears, fur etc. At about 22 weeks, its eyes open and it begins to peep out of the pouch. From about 22 to 30 weeks, it begins to feed upon a substance called "pap" which the mother produces in addition to milk. Pap is a specialised form of faeces, or droppings, which forms an important part of the young koala's diet, allowing it to make the transition from milk to eucalyptus leaves, rather like a human baby is fed "mushy" food when it starts to eat solids. Pap is soft and runny and thought to come from the caecum(a blind ended pouch at the junction of the small and large intestines). It allows the mother to pass on micro-organisms present in her own digestive system which are essential to the digestion of eucalyptus leaves.It is also a rich source of protein.

The joey leans out of the pouch opening on the centre of the mother's abdomen to feed on the pap, stretching it open towards the source of the pap. The baby feeds regularly on the pap and as it grows it emerges totally from the pouch and lies on its mother's belly to feed. Eventually it begins to feed upon fresh leaves as it rides on her back. The young koala continues to take milk from its mother until it is about a year old, but as it can no longer fit in the pouch, the mother's teat elongates to protrude from the pouch opening. Young koalas remain with their mothers until the appearance outside the pouch of the next season's joey. It is then time for the previous year's joey to wean and find its own home range. If a female does not reproduce each year, the joey stays with her longer and has a greater chance of survival when it does leave its mother.

Females generally live longer than males as the males are more often injured during fights, they tend to travel longer distances with the resulting increase in risks such as cars and dogs, and they more often occupy poorer habitat. Putting a life span on the average koala can be misleading because some survive only for a period of weeks or months, while others survive to old age. Koalas living in an undisturbed habitat would have a greater life expectancy than those living in suburbia. Some estimates for the average life-span of an adult wild male koala are ten years, but the average survival rate for a dispersing sub-adult male living near a highway or a housing estate is closer to two or three years.

There are always some transient animals who hang around the edges of stable groups. They are usually young males and will often drift between breeding aggregations waiting for an opportunity to become a permanent resident.

Threats

Since European settlement, approximately 80% of Australia's eucalypt forests have been decimated. Of the remaining 20% almost none is protected and most occurs on privately-owned land.

Settlers favoured the rich fertile lands along the eastern seaboard to have their farms and urban developments. Unfortunately, this is where the majority of koalas are already living because they also like to live in trees which are growing in fertile soils.

The main causes of loss of habitat include:

LAND CLEARING

Clearing of the land for expansion of human settlement eg:-
agriculture, housing, mining, forestry,factories and roads.
The results of this would include:-
· loss of habitat
· increased disturbance by humans
· injury or death from traffic
· injury or death from dogs and cats
· effects of garden pesticides getting into waterways
· increased competition for food and territory because of overcrowding
· increased stress on animals, making them more susceptible to disease.

It has also been documented that over 4000 koalas are killed each year by dogs and cars. It easy to see that the biggest threat to the Koala population is the human.

BUSHFIRES

Koala populations in fragmented areas of bushland are at great risk of localised extinction from a single fire which may wipe out an entire habitat. Bushfires are extremely common in the Summer months.

DIEBACK

Changes in the balance of the ecosystem can lead to dieback of trees. The cutting back of the original vast forests has created patches of forest separated from each other by treeless land. Small, isolated patches of forest are prone to dieback. Dieback is a general term for the gradual dying of trees due to factors such as land degradation, leaching of soil nutrients, changes in the composition of vegetation communities, rising water levels underground, salination of the soil, erosion caused by wind and water, exposure to weather and excessive defoliation (or loss of leaves).

The underlying cause of all these factors appears to be the clearing and disturbance of forests. Seventy five percent of the main koala food tree species are declining in numbers as a result of this.

OTHER THREATS

Today the natural predators of the koala do not make a significant impact on wild populations.They include goannas dingoes, powerful owls, wedge-tailed eagles, and pythons, all of which are most likely to prey upon juvenile koalas.

Feral animals are another threat koalas have had to face since European settlement. Foxes have been blamed for preying upon young koalas when their mother descends to the ground to change trees, and large feral cats may also be a problem for young koalas.

Long droughts also have an effect on the Koala population

DISEASE

Disease is part of the natural history of the koala. There are 4 common koala diseases caused by the chlamydia organism: conjunctivitis which can cause blindness, pneumonia, urinary tract infections and reproductive tract infections, which can cause female infertility. The symptoms of chlamydia manifest as sore eyes, chest infections, and "wet bottom" or "dirty tail". Different strains of chlamydia bacteria are thought to cause these diseases. In 1995, scientists isolated two strains called chlamydia pecorum and chlamydia pneumoniae.

Scientists now believe that the chlamydia organism has been occuring amongst koala populations for many years, and has acted as a natural population control in times of stress. The organism is harmless in populations with unlimited resources, but manifests in times of stress, such as happens when habitat is reduced. The weaker animals succumb to the disease, become sick, infertile or die, leaving the genetically stronger animals to continue breeding. In disease-free populations which have been moved to areas where they were not native or where there is not enough habitat to support them (such as on some islands off Victoria and Kangaroo Island in South Australia), problems with overpopulation have arisen because of this unnatural situation. However, this is not the case in most mainland populations, and indeed many of the mainland colonies are in decline. Koalas also suffer from a range of cancers like leukemia and skin cancers.

Great Koala/ Australian Wildlife Links

The Australian Koala Foundation

Lone Pine Koala Sanctuary

Friends of the Koala (Phillip Island,Victoria)

Friends of the Koala (N.S.W)

Wildlife Victoria Wildlife Emergency Rescue-Victoria

Wildlife Preservation Society of Australia

Bibliography

I have purposely placed all this information on one page to make it
easier for the student to obtain relevant information for projects.
Apart from first hand information received from the Wildlife Parks noted
below, information on this site was also obtained from a number of
other sources and I would like to acknowledge them.

  • The Australian Koala Foundation
  • Lone Pine Koala Sanctuary
  • Websters Australian Mammals CD Rom
  • Wild Australia-M.K.Morcombe Lansdowne Press
  • Animal World Encyclopaedia-Paul Hamlyn

    I have also visited

  • Healesville Sanctuary (Victoria)
  • Melbourne Zoo (Victoria)
  • Phillip Island Nature Park(Victoria)
  • Currumbin Wildlife Sanctuary (Queensland)
  • Kyabram Fauna Park (Victoria)
  • Australia Zoo (Queensland)
  • Bimbimbie Wildlife Park (Victoria)
  • Taronga Zoo (New South Wales)
  • Sydney Wildlife World (New South Wales)
  • David Fleay's Wildlife Sanctuary (Queensland)
  • Adelaide Zoo (South Astralia)
  • Cleland Wildlife Park (South Australia)
  • Ballarat Wildlife Park ( (Victoria)

    and would like to thank staff there for their valuable
    contribution to information.

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