Sunday, May 5, 2013

K (part 1) is for KOALA

The koala is a small bear-like, tree-dwelling, herbivorous marsupial which averages about 9kg (20 lb) in weight.  Its fur is thick and usually ash grey with a tinge of brown in places.  It 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 when there is not enough moisture in the leaves, i.e. 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.

Koalas are found in a range of habitats, from coastal islands and tall eucalypt forests to low woodlands inland.  Today they are found in Queensland, New South Wales, Victoria and South Australia.  Their range extends from the Atherton Tableland west of Cairns in Queensland to islands off the coast of Victoria and South Australia in the south, and west to central and western Queensland, 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 lare enough to support a healthy population and to allow for expansion by maturing young koalas.  They are highly territorial and in stable breeding groups, individual members of koala society maintain their own 'home range' areas.  These areas vary in size depending on the habitat quality of bushland which can be measured in terms of density of key food trees.  These trees define the boundaries of the individual hoala's home range and can be likened to surveyor's 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.

Koalas are fussy eaters and research has revealed that stable koala populations will only occur in a suitable habitat where their preferred gum leaves are available and this can depend on suitable soil types and adequate rainfall.  In Australia there are over 600 types of eucalypts, but koalas will only eat 40-50 varieties with only about 10 being preferred.  Different types 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.  Each koala eats approximately 200 to 500 grams of leaves each day.  The teeth are adapted to deal with this; the sharp front incisors nip the leaves from the branches and the molars (back teeth) are shaped to allow a koala to cut and shear the leaves rather than just crush them.  A cap 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 as it has an excellent sense of balance and its body is lean and muscular and its quite long, strong limbs support it 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 and 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 koala can weight up to 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 se koalas in Queensland, they look noticably smaller than koalas in Victoria.

Koalas are mostly nocturnal animals, mostly active during the night and at sawn and dusk.  In the cooler hours they are less likely to lose precious moisture and energy than during the hotter daylight hours.  An average of 18 to 20 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 which is necessary to differentiate between types of gum leaves and to detect whether the leaves are poisonous or not.  It'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 oils 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.

When approaching trees from the ground koalas spring from the ground and catch their front claws in the bark and 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 sleeping postures and they will move around the tree during the day and night to catch the sun or 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 descent to the ground to change trees and it is there that they are mot vulnerable to predators such as dogs, foxes and dingoes, and also to the risk of injury or death from cars and other vehicles.  They walk with an awkward-looking gait and can also run.  They have sometimes been observed swimming but this is nor a regular occurrence.

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 it 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.

The 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 given 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 displease 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 and is often accompanied by shaking.  Koalas also communicate by marking their trees with scent.

Marsupials such as koalas are differentiated from other mammals in that they give birth to immature young which then develop further in a pouch.  The word 'marsupial' from the Latin word "marsupium, meaning 'pouch'.  Most, but not all, marsupials have a pouch in which to raise their young.

The breeding season runs roughly from September to March and females generally begin breeding at about 3 or 4 years of age and usually produce only one offspring each year.  Once a female has conceived it is only 34-36 days before the birth of the new baby called a 'joey'.  The tiny baby is roughly 2 cms long and weighs less than 1 gram, looking rather like a pink jellybean as it is totally hairless, blind and has no ears.  It makes its way to the pouch unaided and once inside it attaches itself to one of the two teats which swells to fit its mouth.  This prevents the joey being dislodge from its source of food.  The mother contracts the sphincter muscle at the pouch opening to prevent the baby from falling out.

The joey 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 and at about 22 weeks its eyes open and it begins to peep out of the pouch.  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 it own home range.  It 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.

Since European settlement approximately 80% of Australia's eucalypt forests have been decimated and 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 koala habitat include:  clearing of land for human settlement, i.e. 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 and increased stress on animals, making them susceptible to disease.

It has been documented that over 4,000 koalas are killed each year by dogs and card so it is easy to see that the biggest threat to the koala population is the human.   There are many other threats to the koalas since human settlement including bushfires, dieback, feral animals such as foxes which 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 a big effect on koala populations and disease also can decimate a koala population and many of the mainland populations are in decline.  Scientists now believe the chlamydia organism has been occurring amongst koala popoulations for many years and has acted as a natural population control in times of stress. In disease-free populations which have been moved to areas where the koala was not native to or where there is not enough habitat to support them (such as some islands off Victoria and Kangaroo Island off South Australia) problems with overpopulation have arisen because of this unnatural situation of there being no disease present.  Koalas can also suffer from a range of caners like leukemia and skin cancers.

I am sorry this post if so long but I found so many interesting facts about our beloved koalas, a beautiful animal that must be protected at all costs for its own sake and for future generations to love and wonder at.  I did try to condense some of the facts and hope I've not changed them in any way.  There is so much more to learn about the koala that I've not been able to write here.

P.S.  In regard to koalas drinking I have received pictures of koalas on very hot days going to people and asking for water and seen them drinking from water bottles etc.  There is also a very famous picture taken after the devastating bushfires in Victoria in 2009 (173 people perished and 7,500 were left homeless) of the koala (to become known as Sam the Koala) being given a drink of water by  firefighter David Tree.  Sam was subsequently taken to the Southern Ash Wildlife Centre where she was found to be suffering from second-degree burns to her paws and she was given painkillers.  Caretakers estimated it would take her about 8 months to recover.  Based on the condition of her teeth, the shelter manager estimated her to be between 2-4 years old.  Sam was placed with a male koala named Bob who had been rescued from another bushfire area 2 days earlier and was suffering from third-degree burns.  Sadly Sam had to be euthanised just months after her rescue when she was diagnosed with cysts linked to the life-threatening disease chlamydia that has ravaged koala populations.  Sam was due to have surgery but John Butler of the Morwell Vet Clinic discovered Sam had severe changes in her urinary and reproductive tract that were non-operable.  It was so severe that there was no possible way to be able to manage her pain.   RIP Sam.


  1. They are so sweet...and amazing that they are so approachable in the wild.

  2. Actually they are not that approachable in the wild as I think it is only when they are in need that they allow contact with humans. In captivity you can cuddle them and have your photo taken with them. I am told they can scratch at times if you're not careful so perhaps not always cuddly. We all love them though regardless.