The Koala (Phascolarctos cinereus) is a thickset arboreal marsupial herbivore native to Australia, and the only surviving representative of the family Phascolarctidae.
The Koala is found all along the eastern coast of Australia from near Adelaide to the southern part of Cape York Peninsula. The Koalas of South Australia were largely exterminated during the early part of the 20th century, but the state has since been repopulated with Victorian stock. The Koala is not found in Tasmania or Western Australia.
Taxonomy and evolution
A typical Victorian Koala (formerly P. cinereus victor) has longer, thicker fur, and is a darker, softer grey. It often has with chocolate-brown highlights on the back and forearms. It has a more prominently light-colored ventral side, fluffy white ear tufts. Typical weights are 26.46 lb (12 kg) for males and 18.74 (8.5 kg) for females. In tropical and sub-tropical Queensland, the Koala is smaller at around 14.33 lb (6.5 kg) for an average male and just over 11.02 lb (5 kg) for an average female. It has a lighter, often rather scruffy grey in color fur that is shorter and thinner. In Queensland the Koala was previously classified as the subspecies P. cinereus adustus, and the intermediate forms in New South Wales as P. cinereus cinereus. The variation from one form to another is continuous and there are substantial differences between individual Koalas in any given region such as hair color. Koala fossils are quite rare, but some have been found in northern Australia dating to 20 million years ago. The Koala did not specialize in a diet of eucalyptus until the climate cooled and eucalyptus forests grew in the place of rainforests. The fossil record indicates that before 50,000 years ago, Giant Koalas inhabited the southern regions of Australia. The Koala fills the same ecological role as the sloth of South America.
The Koala is broadly similar in appearance to the wombat (its closest living relative), but has a thicker, more luxurious coat. It has much larger ears and longer limbs, which are equipped with large, sharp claws. They assist with climbing. Weight varies from about 30.86 lb (14 kg) for a large, southern male, to about 11.02 lb (5 kg) for a small northern female.
Contrary to popular belief, their fur is thick, not soft and cuddly. Koalas’ five fingers per paw are arranged with the first two as opposable thumbs, providing better gripping ability.
The Koala has an unusually small brain, with about 40% of the cranial cavity being filled with fluid. The brain itself is like “a pair of shriveled walnut halves on top of the brain stem. They do not contact each other or the bones of the skull. It is the only animal on Earth with such a strangely reduced brain.
It is a generally silent animal, but males have a very loud advertising call that can be heard from almost a .63 miles (kilometers) away during the breeding season. There is little reliable information about the lifespan of the Koala, but in captivity they have been observed to reach the age of 15 years.
Females reach sexual maturity at 2 to 3 years of age, males at 3 to 4 years. If healthy, a female Koala can produce one young each year for about 12 years. Gestation is 35 days; twins are very rare. Mating normally occurs between December and March.
A baby Koala is referred to as a joey. It is hairless, blind, and earless. At birth the joey, the size of a jellybean, crawls into the downward-facing pouch on the mother’s belly (which is closed by a drawstring-like muscle that the mother can tighten at will) and attaches itself to one of the two teats. The downward-facing pouch provides a much shorter trip from the birth canal to the pouch than in other marsupials. Thus, the forearms need not be as developed for the journey into the pouch, and can develop more fully for excellent climbing ability later in life. Young remain hidden in the pouch for about six months, only feeding on milk. During this time they grow ears, eyes, and fur. The joey then begins to explore outside of the pouch. At about 30 weeks it has begun to eat the semi-liquid form of the mother’s excrement called “pap”. The baby Koala will remain with the mother for another six months or so, riding on her back, and feeding on both milk and gum leaves until weaning is complete at about 12 months of age. Young females disperse to nearby areas at that time. Young males often stay in the mother’s home range until they are two or three years old.
Ecology and behavior
The Koala lives almost entirely on eucalyptus leaves. Like wombats and sloths, the Koala has a very low metabolic rate for a mammal (which conserves energy) and rests motionless for about 19 hours a day. It sleeps most of that time. Koalas spend about 3 of their 5 active hours eating. It feeds at any time of day, but usually at night. An average Koala eats 1.1 lbs (500 grams) of eucalyptus leaves each day. It chews them in its powerful jaws to a very fine paste before swallowing
The Koala will eat the leaves of a wide range of eucalypts, and occasionally even some exotic species. It has firm preferences for particular varieties. These preferences vary from one region to another. In the south Manna Gum, Blue Gum and Swamp Gum are favored. Grey Gum and Tallow wood are important in the north. The ubiquitous River Red Gum of the isolated seasonal swamps and watercourses that go across the dry inland plains allows the Koala to exist in surprisingly dry areas. Many factors determine which of the 800 species of eucalyptus trees the Koala eats.
The Koala was hunted almost to extinction in the early 20th century, largely for its fur. In recent years, some colonies have been hard hit by disease, especially chlamydia. The Koala requires large areas of healthy, connected forest and will travel long distances along tree corridors in search of new territory and mates. The ever-increasing human population of the coastal parts of the continent continues to cut these corridors by agricultural and residential development, forestry and road building. This leaves Koala colonies in decreasing areas of bush. These pieces need to be managed, protected and restored in a coordinated way. Presently, many are being lost to weeds, cleared for agriculture, or carved up by developers. Other threats come from logging, poor management, attacks from feral and domestic animals, disease and roads.
In contrast to the situation on much of the mainland, where populations are declining, the Koalas of many island and isolated populations have reached what some have described as “plague” proportions. On Kangaroo Island in South Australia, Koalas introduced some 90 years ago have thrived in the absence of predators and competition. Combined with an inability to migrate to new areas, this has caused the Koala populations to become unsustainable and threaten the Island’s unique ecology. Koala numbers are estimated at over 30,000, with ecologists suggesting that the Island can sustain 10,000 at most. The Koala occurs in four Australian states
Koalas as pets
In spite of their looks, people generally do not have Koalas as pets. This is because they are unsuited to a suburban environment. It is illegal to do so in Australia.
The Koala is one of the few mammals (other than primates) that have fingerprints. In fact, koala fingerprints are remarkably similar to human fingerprints, even with an electron microscope. It can be quite difficult to distinguish between the two.