Zookeeper Journal



Koala
(Phascolarctos cinereus)

Status in the Wild: Threatened

Spider webs crisscross the dry undergrowth, sparkling beneath the tall gum trees whose dense canopies sway gracefully in the summer breeze.  Symphonies of buzzing insects accompany the snapping and crackling of fallen eucalyptus leaves under a hiker's boots.  

The Australian bush is home to many animals, including several varieties of birds and insects, not to mention the spiders, lizards, and snakes, some of which are the deadliest in the world.  Kangaroos, wombats, and spiny insect-eating echidnas are among the small mammals that forage the undergrowth. But the trees belong to the koalas.  

It takes a keen eye to spot koalas in the wild, but from a distance they appear to be inert ash-coloured furballs wedged in the fork of tree branches. Chances are that the koala will be fast asleep.  

In the animal kingdom, koalas take the gold for sleeping, which is anywhere from 19 to 22 hours a day, spending as much energy per day as there is in 200 grams of breakfast cereal.  

 

Although they seem to be the laziest mammals on earth, there is something special about koalas that draw our fascination.  Perhaps it is their peculiar habit of sitting upright when they sleep. Or maybe it's because they're just downright cute! 

 


Australia's national icon, koalas have become international heartthrobs. Yet, as much as we adore these animals, humans are destroying their habitat at an alarming rate.

Early Australian settlers described koalas using familiar European terms such as sloths, monkeys, bears and even monkey bears.  Although the name 'koala bear' persists today, they are not bears but marsupials.  

These are mammals that have no placenta and give birth to immature young that develop in a pouch on the mother's abdomen.  Koalas belong to the order Marsupialia, which includes kangaroos, wombats, and possums.

Koalas are among the world's largest arboreal (tree-dwelling) mammals, weighing between 4 and 14 kg, roughly equivalent to a sack of flour.  Males are up to 50 percent larger than females, and koalas in Australia's southern region are larger than their northern region counterparts.  

Their most distinguishing facial features include a large nose pad called a rhinarium, sensitive to all the smells of the bush.  Koalas have small forward-facing eyes with slits for pupils.  Their eyesight is generally poor, but they make up for it with their keen sense of smell and hearing.  

Koalas have feet and hands endowed with sharp jet-black claws.  The first two digits of the hands oppose the other three, giving koalas the appearance of having two thumbs.  

This type of hand is called 'forcipate,' a condition that is unusual for mammals, but found in several marsupials.   

 

The koala's feet have what are called syndactylus toes, where the second and third digits are connected by a web of skin, forming, essentially a single digit with two claws.  Syndactylus toes are used like a comb for grooming.  

 

The koala's forelimbs are equal in strength to their hind limbs, and their body is lean and muscular giving them extra strength for climbing. 

Their short, thick fur provides koalas with the best insulation found in marsupials, ranging in colour from light grey to brown, with white patches on the belly, chest and neck.  

On cold days, koalas huddle in a ball, exposing the dark fur on their back to absorb heat from the sun.  On hot days, koalas expose more of the white fur on their belly, which reflects heat, and they sometimes dangle their short, stocky arms and legs over the branches.  People have mistakenly attributed this pose to the koala getting drunk on gum leaves. 

Koalas are generally nocturnal, sleeping during the heat of the day and coming down the tree at night.  But on the ground, koalas are most vulnerable to predators such as foxes, dingoes and domestic dogs. Their greatest threat comes from cars, taking up to 4,000 koala lives a year.  

However, in good habitat, koalas can live up to 10 years for males, 15 for females, mainly on a diet consisting of nothing more than eucalyptus leaves. 

 

It was once believed that koalas sleep as much as they do because the eucalyptus oil in the leaves made them drunk.  

On the contrary, the koalas need a lot of energy to digest the tough, fibrous leaves, which are also nutritionally poor.  We could hardly expect to live with much energy on a diet of cardboard

But if we lived on a diet of gum leaves we would quickly succumb to liver poisoning because the eucalyptus oils are toxic.  Koalas are especially adapted to this diet.  No wonder the koala has gum leaves largely to itself!  

To extract enough energy from the gum leaves, koalas eat one to three pounds of leaves a day, sniff-testing each leaf before deciding whether to eat it.  The leaf particles enter the koala's digestive system where material highest in proteins, sugars and fats are stored for up to eight days in the cecum, an appendix as much as eight feet long.  Here, microorganisms break down the potentially fatal toxins in the eucalyptus oil.


Eucalyptus leaves also contain relatively high levels of water, meaning that koalas can get most of their water requirements from the leaves without having to drink.  

In fact, the name 'koala' is thought to have come from an Aboriginal word meaning 'no drink.' Except in severe droughts, koalas rarely have to come down from their tree, except when they move to another tree.



 


 

Gum trees provide koalas their home and food, and each koala has their own territory, called their home range, consisting of several different trees.  Some of these home ranges overlap those of other koalas.  

Male koalas mark their territory using the scent gland in the centre of their chest.  The males rub their chest against trees, which tells other koalas that this tree is taken.  


Although females don't have scent glands like males, it is thought that they mark trees the same way.  Koalas live usually solitary lives in the trees except for mothers with youngsters, called joeys.

Koalas give birth about 35 days after conception to a kidney bean-sized newborn that has not yet fully developed.  Without any assistance from the mother, the newborn instinctively makes its way to the pouch where it attaches itself to one of two teats and hunkers down for the next five months.  

When the mother reckons its time for joey to come out, instead of defecating pellets she starts excreting pap, a slimy, green substance that the joey consumes for about a fortnight.  Once the pap enters the joey's gut, it starts the stomach working so it can break down the toxins in the eucalyptus leaves.  When the pap turns back into pellets, little joey finally comes out for good.

Koalas are fully grown by their third or fourth year and begin breeding between September and March.  Females can have one joey per year, but some produce joeys every two or three years.

Before European settlement began in 1788, there were perhaps many more koalas in Australia than there are today.  The Aborigine people hunted koalas for food and used their fur, but only for their immediate use.  Early settlers discovered that koala fur was a valuable commodity and they hunted koalas in the hundreds of thousands.  From the early 1800ís until the late 1920ís, millions of koalas were hunted and killed for their fur.  

At the same time, the koala integrated itself into children's stories and gained popularity as part of Australia's heritage.  Increasing numbers of Australians formed the opinion that koalas need to be cherished and protected.  Many began to voice opposition to the fur trade that was taking a huge toll on the koala populations.  Their words often fell on deaf ears.

As a result of the fur trade, by 1924, koalas became extinct in South Australia, and their numbers were severely low in Victoria and New South Wales.  Up north, Queensland was the koalas' only remaining stronghold in Australia.  Following public outcry after the devastating 1919 koala hunting season, the Queensland government halted hunting until further notice, not to preserve the koala species, but to avoid over-exploitation by trappers.  

In 1927, despite much protest, the government again allowed another open season on koalas.  In just 31 days an estimated 800,000 koalas were killed.  This time, public outrage was so overwhelming that the Queensland government banned hunting koalas indefinitely.  By the late 1930ís koalas were made a protected species throughout Australia.  Unfortunately, their habitat never received the same protection.

Today, there is no doubt that the clearing of forests has caused serious problems for koalas - they are dying out at alarming rates in places.  Houses, motorways, fields, and golf courses have separated ever-shrinking colonies and inbreeding threatens to impoverish the genetic stock of the species.  

Thus weakened, koalas are especially vulnerable to disease such as chlamydia. Aggravated by environmental stress, chlamydia infections, a bacterium that plagues koalas across Australia, can cause conjunctivitis, urinary-tract disorders, sterility, and even death.

In modern times, the loss of habitat has led to the extinction of 20 Australian mammal species, 10 of them marsupials.  This figure is about half of the modern world total for mammal extinctions, a record no other country can match. In 1992, the International Union for Conservation of Nature and Natural Resources listed 59 threatened Australian marsupials.  Half came under the headings 'endangered' and 'vulnerable,' and half, the koala among them, were judged 'potentially vulnerable.'


No one knows how many koalas remain in Australia.  Estimates range anywhere from 10,000 to 500,000. 

In Queensland alone, the Australian Koala Foundation estimates a figure of 25,000 to 50,000 koalas, and the numbers are falling, which makes for a good argument to put them immediately on the endangered species list in the hopes of preventing any further population-slide.


 
 

More work needs to be done on the details of the koala's habitat needs: how widely they range and what particular eucalyptus leaves they prefer.  In the absence of concrete scientific evidence, debate about their status in the wild is emotionally charged.  

The term 'koala politics' is used to explain the often-heated differences in opinion about how the animal is faring.

However, there's much more than koalas at stake.  They are a prime indicator of the biodiversity of Australia's forests.  If old trees go, they'll take with them not only koalas but also birds, fungi, and who knows how many insects. The koala is extremely important as a flagship species when you're trying to save an entire ecosystem.  Call it koala power!

What's being done?  Citizens groups are working to stop motorway construction; dog owners leave their dogs in at night; home owners are planting more trees; organisations such as the Australian Koala Foundation are conducting habitat studies and raising awareness; zoos, wildlife parks and sanctuaries are looking after koalas in captivity, making valuable contributions to the conservation of the species.

Perhaps the greatest hope for koalas is creating legislation to protect the gum trees. People are responsible for the koala's legacy, a difficult task for any one organisation or government agency.  Using the best information, combined with our compassion, we can save what is left of the koala's habitat.  

Our connection with nature means that the loss of any animal becomes a loss of our own. What will we become if the animals are gone forever?

 

 

Sources and Suggested Readings

Archer, Michael.  Koala: Australia's Endearing Marsupial.Frenchs Forest, NSW: Reed Books Pty, Ltd., 1987

Sharp, Ann. The Koala Book. Gretna, Louisiana: Pelican Publishing Co., Inc., 1995

Australian Koala Foundation. Brisbane QLD, Australia. 2002 www.savethekoala.com.

Lone Pine Koala Sanctuary. Brisbane QLD, Australia, 2002 www.koala.net