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On the road to Cape Otway, there were a couple of these lovely Koala’s sitting in the trees along the roadside. Many tourists had stopped for this unique photo opportunity.
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. 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.
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.
Fuji S200EXR camera