The Diet and Behavior of Koalas

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"The Diet and Behavior of Koalas"
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Koalas have a reputation as passive animals that spend most of their time "vegging out" in gum trees. You can't really imagine a koala running a marathon - though acclaimed children's author, Mem Fox did write a delightful story book about "Koala Lou", a joey who took part in a bush race.

It's no wonder koalas always seem sleepy when we see them. For starters, they are nocturnal and mostly active after sunset. During the day they doze in the fork of a gum tree. They are never terribly active though, sleeping about 75 per cent of their lives (16 hours a day).

This is because their diet doesn't provide them with oodles of energy and they have to use every strategy in the book to conserve it efficiently. Their main source of nourishment is eucalyptus leaves. They rarely eat anything else, though they sometimes include leaves of other trees such as the wattle, tea tree and paperbark.

Eucalyptus leaves are not exactly a koala's equivalent to a "Big Mac". They neither fatten nor fill in a hurry. They are downright hard work - full of fibre and deficient in calories. So koalas have a challenge just meeting their bodily needs of fuel and nutrition. Their metabolic rate is appropriately slow to maximize their energy source and enable them to retain their food within their digestive system as long as possible. This means they can extract optimum energy from it. Koalas have to work their way through up to 500 grams (1 lb) of leaves each day.

Eucalyptus leaves are actually toxic to most animals. Some people claim the koala is so sleepy because it's drunk on the effects of gum leaves. This is a myth. The koala has a specially-adapted digestive system that detoxifies the chemicals in the leaves which would poison other animals.

Obviously koalas think they're the only offering on the forest menu worth eating. But I can't say the thought of just eating one thing all day every day is exactly inspiring - especially when it produces so little energy and is essentially poisonous. There's a saying that one man's meat is another man's poison. In this case, one critter's salad is another critter's poison.

Koalas have an amazingly efficient digestive organ called a caecum. While the organ is not actually unique to their species, at 200 cm it's considerably longer than that of other animals, including humans - and has a blind end. It contains millions of bacteria that break down the fibrous gum leaves, reducing them to substances that are easier to absorb. Even then, koalas can still only absorb 25 per cent of the fibre they consume - which is why they have to eat such a lot of leaves to compensate.

With all that eucalyptus intake too, it's no wonder koalas often smell like cough drops.

Koalas are very fussy about which eucalyptus leaves they eat. While there are some 600 eucalyptus varieties, koalas only eat about 120 of them. In any given area they may only fancy approximately four to six varieties. For this reason they can't be easily relocated. Wherever you go in Australia you would find different eucalyptus species. Therefore a koala in South Australia would naturally dine on leaves of different flavours to those that make up the diet of a koala in a New South Wales colony.

In any given area there may be as little as one - and on average no more than two or three eucalyptus species that the koalas will browse regularly. Others may only be browsed from time to time or even just used for relaxing and sleeping in. I guess it's like they treat certain trees as kitchens and dining rooms and others as bedrooms and lounge rooms.
The name "koala" is said to be aboriginal for "no drink". They derive most of their hydration from gum leaves, which are 50 per cent water. Occasionally they drink at the edges of streams - mostly during droughts when the gum leaves are unusually dry.

Gum trees provide the koala with its home as well as food. They spend most of their time in their favourite trees, only coming down occasionally to seek shade or sunshine or to climb another tree - maybe just for a change of scenery or because they fancy something different to eat. Sometimes they will jump from one tree to another.

Koalas live in eucalypt forests of eastern and SE Australia - never in rainforests or deserts. Their choice of habitat is essentially based on two vital criteria - the presence of other koalas and the types of eucalypts they favour.

They are, in one respect solitary animals. While you will often see a mother koala with its baby (joey), they don't live in families. However, they do have complex societies. An individual koala will have a certain area of the forest that it possesses as its own space. This is referred to as its home range space and it overlaps the home range spaces of other koalas. It visits the trees that occupy this space regularly. However, except when they are breeding, koalas rarely visit each other's trees. The size of an individual koala's home space depends on such factors as gender, age, habitat and the koala's social position in the colony. Male koalas use a dark scent gland in the centre of their chests to mark their territory.

It's important that a koala finds its own home range by the time it's fully-grown. They may find one that's vacant as a result of another koala dying. Or it could be in a new area of the forest. This is one of the reasons koalas need extensive areas of habitat available.

Koalas use a range of noises to communicate. If they are scared they make a fearsome shriek which sounds similar to a baby wailing. A mother and baby communicate with each other by gentle clicking, squeaking sounds and soft humming or murmuring sounds. A characteristic male koala noise sounds like a snore and a belch. This is referred to as a bellow. I imagine there would be some women who may think their husbands behave like koalas in this respect. The male koala uses this bellow to announce its physical and social position and assert its dominance without having to waste too much energy by fighting. A bellow might well be translated as "I'm Super Koala! Hear me roar!" It's also used to help others identify exactly where the caller is located. Female koalas make a snorting sound to indicate they are ready to mate.

Although they're not highly sociable animals, they do need some contact with other koalas. This is another reason why it's important for them to have areas of suitable eucalyptus forest sizable enough to cater for a healthy koala population. If there's not enough trees to sustain the colony, they will eventually become hungry, malnourished and sick.

It's interesting that even when a koala dies, other koalas won't normally take over its home space for a year or so - or until the scent and other markings of its previous owner have faded away. So there is honour even amongst wild creatures.

Koalas breed once a year. They generally mate between September and March (the beginning of spring till the beginning of autumn in Australia). Females mostly begin breeding at about three or four years of age and at most only give birth to a single joey annually. Twins are rare though not unheard of. Most female koalas only have an average of six joeys in their lifetime. They might only have one every two or three years as they age.

The gestation of a joey is 35 days. When it's born it looks like a pink jellybean. It's naked, blind and its ears have not yet developed. However, nature provides it with other amazingly keen senses, an instinctive sense of direction and strength in its forelimbs and claws to make its way to its mother's pouch. Once there, it latches onto one of the two teats, which swells in its mouth so it stays attached. The mother has a strong sphincter muscle at the opening of her pouch. She contracts this to prevent the joey from falling out. Junior is safely and securely tucked away in its mother's backward facing pouch, where it will spend the next six months of its development.

Joeys stay with their mother until the next season's bub exits the pouch. If its mother doesn't have another joey the following year it gets to stay with her for longer than it otherwise would and this increases its chances of survival. So even in the koala world there are advantages for kids of older mothers.

The joey's eyes open at about 22 weeks and that's when it will poke its head out of the pouch for its first peek at the world outside. By 24 weeks it has fur all over and begins to cut teeth. Then by 30 weeks, it will be spending nearly all its time outside the pouch, where it clings to its mother's abdomen.

About six weeks later it will weigh about a kilogram and it doesn't go back into the pouch any more. By now it's spending a lot of time sitting on its mother's back. If the weather is cold or wet though it seeks protection under her tummy again and sleeps there as well.

At 37 weeks it begins to experiment with independence, moving away from its mother just a tad. However, Mum's slightest movement sends it scurrying back to her. At 44 weeks it still makes sure it doesn't put more than a metre (about 3 ft) between itself and its mother, but by 48 weeks it's becoming more daring. By now mum and bub will often sleep with their backs to each other. If another joey is about to venture out into the world, the elder sibling will move out to make its own way in the world when it's about 12 months old. By then it weighs just over 2 kilograms (4 lb).

The joey's diet consists only of its mother's milk for the first six or seven months of its life. Then at about 30 weeks it's introduced to pap, which it has in addition to milk. Pap is a soft runny substancesimilar to droppings which the mother koala produces to give the joey extra nourishment and to help prepare it for eating eucalyptus leaves. It enables the mother to pass on essential micro-organisms from her own digestive system. It's also rich in protein. The joey will continue drinking its mother's milk until it's about a year old. However, because it can no longer fit in her pouch, it has to pull one of her teats outside the pouch. Fortunately for mum, the teat elongates for this purpose.

Eventually the joey begins feeding on eucalyptus leaves as it rides around on its mother's back.

When koalas lose their habitat they become extremely vulnerable. Not only are they more likely to be preyed upon by dogs or cars but they can also become sick, infertile and die from a condition called chlamydia.

The majority of healthy koalas actually have the chlamydia organism residing in their body tissues. It mainly only makes them ill if they become stressed. The main causes of stress are destruction of their habitat - due to bush fires or land clearing - and the consequent loss of their favoured food supply, as well as having to contend with predators and cars.

Koalas are obviously very sensitive animals. They are somewhat introverted in personality and can be cranky, aggressive and unsociable. But, let's face it, they're common human traits too. Koalas, however, have a distinct advantage of being very cute and appealing. So let's hope they can win enough friends and influence enough people to make their future a lot rosier (or maybe in their case that should be 'gummier') than their past has been since white settlement of Australia.








More about this author: Ruth Woodhouse

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