The
Koala (Phascolarctos cinereus)
The koala's scientific name comes from phaskolos meaning 'pouch' and 'arktos'
meaning bear. The cinereus part means 'ash-coloured'. Some people refer to
the koala as a koala bear, but this is incorrect, since koalas are not part
of the bear family. This mistake goes back to the early 1800s when the taxonomy
of the koala was not fully understood. The word "koala" comes from
an Aboriginal word meaning "does not drink." This again is technically
incorrect - koalas do occasionally drink. They do, however, gain most of the
water they need from their food and from dew that has formed on leaves.
Koalas are found all along the eastern coast of Australia and as far
inland as there is enough rainfall to support suitable forests.Where suitable
trees are widely spaced koalas need to spend too much time on the ground to
avoid the attention of predators. They are absent from Tasmania.
Physical description
Variations in koalas can be seen across even individual populations. However,
the main observable difference is in size and colouration, with those in the
south generally being heavier, darker and with longer fur than those
in the north. This difference is due to climate - the climate of Victoria
being significantly cooler than that of Queensland - and leads to southern
males (12Kg) weighing nearly twice that of their northern cousin (6.5Kg)
The koala's nearest living relative is the wombat, and this is easy to see.
However, koalas have developed a thicker, softer coat, much larger ears, and
longer limbs, which are equipped with large, sharp claws to assist with climbing,
all adaptations for their arboreal life. Weight extremes are about 14 kg for
a large, southern male, to about 5 kg for a small northern female. They are
usually silent, but males have a loud groan-like call used for
announcing it's presence during the breeding season and females emit
a similarly loud 'scream' when feeling threatened by the presence of a male.
Koalas life span is roughly 8-10 years in the wild and 10-12 years in captivity.
Ecology and behaviour
Koalas live almost entirely on eucalyptus leaves, on average eating 500 to
1000 grams (1.1 to 2.2 pounds) each day. This is likely to be an evolutionary
adaptation that takes advantage of an otherwise unfilled ecological niche,
since eucalyptus leaves are a poor food source, being low in protein, high
in indigestible substances, and indeed would be toxic to most other
species. Koalas are one of only three species (the others being the ring tailed
possum and one of the glider family) that can exist entirely on gum leaves.
Because of the low amount of energy that is derived from this food koalas
have developed a very low metabolic rate compared to other mammals (which
saves energy) and rests for about 20 hours a day, sleeping most of that time.
They will feed at any time of day, but usually at night. The liver neutralizes
the toxic components and the greatly enlarged hind gut extracts the
maximum amount of nutrition from the leaves. When young koalas are being weaned,
the mother passes unusually soft faeces, called pap, on which the young feed.
This pap is rich in the bacteria which help neutralize the toxic components
of the leaves, and thus these essential digestive aids are passed onto her
offspring.
Female koalas are generally solitary but spend much of their adult lives with
young. They have distinct home ranges which only tend to overlap in the more
fertile areas. These territories will be larger where food is scarce. Although
males are not regarded as territorial, they do not tolerate each other, especially
during the breeding season when dominant males attack subordinate ones. Most
adult males carry scars about the head and arms as a result.
Koalas are almost completely tree dwelling. They make use of a large bony
plate in the lower back to rest comfortably in a tree fork or on a branch.
They have long claws and a powerful grip which they use for climbing easily
through trees. Motion is normally sedate but can be surprisingly rapid when
required. The are comfortable hopping between branches and when on the ground
will break into a gallop if threatened, whence they will rapidly climb the
nearest tree and wait patiently for the danger to pass. If a predator follows
the koala up a tree it is not unusual for the koala to urinate on its follower
in order to deter it. Koalas are proficient swimmers, although this behaviour
is rarely witnessed.
Reproduction
Males
reach sexual maturity at 3 to 4 years old, females at 2 to 3 years. If the
female remains healthy and the food supply is adequate, a female koala can
produce one young each year for the remainder of her life. Mating normally
happens between December and March, the Southern Hemisphere's summer, and
gestation is 35 days.
The baby koala is known as a joey and is hairless, earless and blind. At birth
the joey, the size of a jelly bean, crawls into the mother's downward-facing
pouch and attaches itself to one of the two teats. The teat will then swell
into the joeys' mouth, thus preventing it from becoming detached. Here it
remains hidden for about six months, only feeding on milk. By the end of this
period the joey will have grown eyes and ears and will then start to emerge
from the pouch for the first time. It is at this time that the joey will feed
on it's mothers' pap. Weaning will not be complete for another six months,
during which time the joey will stay close to its mother, usually either
on her back or chest. Over this period its diet will gradually change until
it is exclusively feeding on gum leaves. Young males may stay within their
mother's home territory until they are two or three years old.
Conservation
status
The koala has long been hunted by aborigines for food but was hunted close
to extinction by European settlers in the early 20th century, largely for
its fur. Indeed, by the 1920s the koala was absent from South Australia and
close to extinct in Victoria. Hunting of koalas was outlawed across Australia
in the 1930s. Since then the threat to koalas has come mainly from habitat
loss. Koalas rely on large areas of connected corridors of forest for a continuous
supply of fresh leaves but pressure for alternative land uses (housing, farming,
roads etc) has led to widespread fragmentation of eucalyptus forests. These
remaining patches of forest are often not of sufficiently high quality
for a population to remain healthy. Other threats to koalas have come from
the spread of disease (chlamydia), from road traffic and from domestic and
feral dogs. There is little agreement as to the actual number of wild koalas
but it is accepted that the population is in decline and remains well
down on the pre-large-scale hunting days.
There are many island and isolated populations where koala populations have
flourished to such an extent that some regard them as a pest due to the damage
inflicted on trees. Kangaroo Island, in South Australia, introduced koalas
early in the 20th century in order to help protect the species. Here they
have thrived due to the lack of competition and predation, the estimated population
now being approximately 30,000. Many blame this "over-population
" for the widespread destruction of local gum species and so have called
for a cull to bring the population down to a more "manageable" 10,000.
However, there is much disagreement on the way forward, with others suggesting
the cause of tree death is in fact disease and suggesting that the problem
is not too many koalas but too few trees. They suggest the way forward is
tree protection and tree planting rather than culling. So far culling has
proved politically unacceptable as there would undoubtedly be an international
backlash. Sterilization and re-location programmes have so far had only limited
success in reducing numbers and remain expensive.
Main sources for this information:
Wikipedia
The Australian Koala Foundation web site
Mammals of Australia, Menkhorst and Knight.
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