The koala ( Phascolarctos cinereus), sometimes inaccurately called the koala bear, is an arboreal herbivorous marsupial native to Australia. It is the only Extant taxon representative of the family Phascolarctidae. Its closest living relatives are the . The koala is found in coastal areas of the island's eastern and southern regions, inhabiting Queensland, New South Wales, Victoria, and South Australia. It is easily recognisable by its stout, tailless body and large head with round, fluffy ears and large, dark nose. The koala has a body length of and weighs . Its fur colour ranges from silver grey to chocolate brown. Koalas from the northern populations are typically smaller and lighter in colour than their counterparts further south. These populations are possibly separate subspecies, but not all researchers accept this.
Koalas typically inhabit open Eucalyptus woodland, as the leaves of these trees make up most of their diet. This eucalypt diet has low nutritional and caloric content and contains toxic compounds that deter most other mammals from feeding on them. Koalas are largely sedentary and sleep up to twenty hours a day. They are asocial; only mothers maternal bond to dependent offspring. Adult males communicate with bellows that intimidate rivals and attract mates. Males mark their presence with secretions from located on their chests. Like other marsupials, koalas give birth to young known as joeys at a very early stage of development. They crawl into their mothers' pouches, where they live for their first six to seven months. They are fully weaned around a year old. Koalas have few natural predators and parasites, but are threatened by such as Chlamydiaceae bacteria and koala retrovirus.
Because of their distinctive appearance, koalas, along with , are recognised worldwide as symbols of Australia. They were hunted by Indigenous Australians and depicted in myths and cave art for millennia. The first recorded encounter between a European and a koala was in 1798, and an image of the animal was published in 1810 by naturalist George Perry. Botanist Robert Brown wrote the first detailed scientific description in 1814 although his work remained unpublished for 180 years. Artist John Gould illustrated and described the koala, thereby introducing the species to the British public. Further details about the animal's biology were revealed in the 19th century by English scientists. Koalas are listed as a vulnerable species by the International Union for Conservation of Nature. Among the many threats to their existence are habitat destruction caused by agriculture, urbanisation, droughts, and associated bushfires, some related to climate change. In February 2022, the koala was officially listed as endangered in the Australian Capital Territory, New South Wales, and Queensland.
Adopted by white settlers, the word "koala" became one of hundreds of Aboriginal loan words in Australian English, where it was also commonly referred to as "native bear", This author strongly deprecated use of another synonym, "sloth". later "koala bear", for its resemblance to a bear. It is one of several Aboriginal words that made it into International English alongside words like "didgeridoo" and "kangaroo".
The koala's genus name, Phascolarctos, is derived from the Greek words φάσκωλος () and ἄρκτος () . The specific name, cinereus, is Latin for .
P. cinereus may have emerged as a dwarf form of the giant koala ( P. stirtoni), following the disappearance of several giant animals in the late Pleistocene. A 2008 study questioned this hypothesis, noting that P. cinereus and P. stirtoni were Sympatry during the mid-late Pleistocene, and that their teeth morphology displayed the major differences. The fossil record of the modern koala extends back at least to the middle Pleistocene.
Other studies have found that koala populations are highly inbred with low genetic variation. Such low genetic diversity may have been caused by population declines during the late Pleistocene. Rivers and roads limit gene flow and contribute to the isolation of southeast Queensland populations. In April 2013, scientists from the Australian Museum and Queensland University of Technology announced they had fully sequenced the koala genome.
The pelage of the koala is denser on the back. Back fur colour varies from light grey to chocolate brown. The belly fur is whitish; on the rump it is mottled whitish and dark. The koala has the most effective insulating back fur of any marsupial and is resilient to wind and rain, while the belly fur can reflect solar radiation. The koala has curved, sharp claws well adapted for climbing trees. The large forepaws have two opposable digits (the first and second, which are opposable to the other three) that allow them to grip small branches. On the hind paws, the second and third digits are fused, a typical condition for members of the Diprotodontia, and the attached claws (which are still separate) function like a comb. The animal has a robust skeleton and a short, muscular upper body with relatively long upper limbs that contribute to its ability to climb. The thigh muscles are anchored further down the shinbone, increasing its climbing power.
For a mammal, the koala has a disproportionately small brain, 60% smaller than that of a typical diprotodont, weighing only on average. The brain's surface is fairly smooth and "primitive". It does not entirely fill the cranial cavity, unlike most mammals, and is lightened by large amounts of cerebrospinal fluid. It is possible that the fluid protects the brain should the animal fall from a tree. The koala's small brain may be an adaptation to the energy restrictions imposed by its diet, which is insufficient to sustain a larger brain. Its small brain limits its ability to perform complex behaviours. For example, it will not eat plucked eucalyptus leaves on a flat surface, which does not match its feeding routine.
The koala has a broad, dark nose with a good sense of smell, and it is known to sniff the oils of individual branchlets to assess their edibility. Its relatively small eyes are unusual among marsupials in that the pupils have vertical slits, an adaptation to living on a more vertical plane. Its round ears provide it with good hearing, and it has a well-developed middle ear. The koala larynx is located relatively low in the vocal tract and can be pulled further down. They possess unique folds in the velum (soft palate), known as velar vocal folds, in addition to the typical vocal folds of the larynx. These features allow the koala to produce deeper sounds than would otherwise be possible for their size.
The koala has several adaptations for its low nutrient, toxic, and fibrous diet. The animal's dentition consists of incisors and cheek teeth (a single premolar and four molars on each jaw) that are separated by a large gap (a characteristic feature of herbivorous mammals). The koala bites a leaf with the incisors and clips it with the premolars at the petiole, before chewing it to pieces with the cusped molars. Koalas may store food in their before it is ready to be chewed.
Koalas are hindgut fermenters, and their digestive retention can last 100 hours in the wild or 200 hours in captivity. This is made possible by their caecum— long and in diameter—possibly the largest for an animal of its size. Koalas can retain food particles for longer fermentation if needed. They are more likely keep smaller particles as larger ones take longer to digest. While the hindgut is relatively large, only 10% of the animal's energy is obtained from digestion in this chamber. The koala's metabolic rate is only 50% of the typical mammalian rate, owing to its low energy intake, although this can vary across seasons and sexes. They can digest the toxic plant secondary metabolites, phenolic compounds and due to their production of cytochrome P450, which neutralises these poisons in the liver. The koala replaces lost water at a lower rate than species such as some possums. It maintains water by absorbing it in the caecum, resulting in drier faecal pellets packed with undigested fibre.
Fossil evidence shows that the koala's range stretched as far west as southwestern Western Australia during the late Pleistocene. They were likely driven to extinction in these areas by environmental changes and hunting by Indigenous Australians. Koalas were introduced to Western Australia at Yanchep in 1938 but that population was reduced to 4 individuals by 2022. Koalas can be found in both tropical and temperate habitats ranging from dense woodlands to more spaced-out forests. In semi-arid climates, they prefer , where nearby streams and creeks provide refuge during times of drought and extreme heat.
Their low-energy diet limits their activity and they sleep 20 hours a day. They are predominantly active at night and spend most of their waking hours foraging. They typically eat and sleep in the same tree, possibly for as long as a day. On warm days, a koala may rest with its back against a branch or lie down with its limbs dangling. When it gets hot, the koala rests lower in the canopy and near the trunk, where the surface is cooler than the surrounding air. It curls up when it gets cold and wet. It resorts to a lower, thicker, branch during high winds. While it spends most of the time in the tree, the animal descends to the ground to move to another tree, with either a walking or leaping gait. The koala usually grooms itself with its hind paws, with their double claws, but it sometimes uses its forepaws or mouth.
Adult males communicate with loud bellows—"a long series of deep, snoring inhalations and belching exhalations". Because of their low frequency, these bellows can travel far through the forest. Koalas may bellow at any time, particularly during the breeding season, when it serves to attract females and possibly intimidate other males. They also bellow to advertise their presence when they change trees. These sounds signal and exaggerate the male's body size; females pay more attention to bellows by larger males. Female koalas bellow, though more softly, in addition to making snarls, wails, and screams. These calls are produced when in distress and when making defensive threats. Younger animals squeak and older ones squawk when distraught. When another individual climbs over it, a koala makes a low closed-mouth grunt. Koalas also communicate with facial expressions. When snarling, wailing, or squawking, the animal curls the upper lip and points its ears forward. Screaming koalas pull their lips and ears back. Females form an oval shape with their lips when annoyed.
Agonistic behaviour typically consists of quarrels between individuals who are trying to pass each other on a tree. This occasionally involves biting. Strangers may wrestle, chase, and bite. In extreme situations, a larger male may try to displace a smaller rival from a tree, chasing, cornering, and biting it. Once the individual is driven away, the victor bellows and marks the tree. Pregnant and lactating females are particularly aggressive and attack individuals who come too close. In general, however, koalas tend to avoid fighting due to energy costs.
Koalas are induced ovulators. The gestation period lasts 33–35 days, and a female gives birth to one joey or occasionally, twins. The young are born tiny and barely formed, weighing no more than . However, their lips, forelimbs, and shoulders are relatively advanced, and they can breathe, defecate, and urinate. The joey crawls into its mother's pouch to continue its development. Female koalas do not clean their pouches, while an unusual trait among marsupials.
The joey latches on to one of the female's two teats and suckles it. The female lactates for as long as a year to make up for her low energy production. Unlike in other marsupials, koala milk becomes less fatty as the joey grows. After seven weeks, the joey has a proportionally large head, clear edges around its face, more colouration, and a visible pouch (if female) or scrotum (male). At 13 weeks, the joey weighs around , and its head doubles in size. The eyes begin to open and hair begins to appear. At 26 weeks, the fully furred animal resembles an adult and can look outside the pouch.
At six or seven months, the joey weighs and fully emerges from the pouch for the first time. It explores its new surroundings cautiously, clutching its mother for support. Around this time, the mother prepares it for a eucalyptus diet by producing a faecal pap that the joey eats from her cloaca. This pap comes from the cecum, is more liquid than regular faeces, and is filled with bacteria. A nine month old joey has its adult coat colour and weighs . Having permanently left the pouch, it rides on its mother's back for transportation, learning to climb by grasping branches. Gradually, it becomes more independent. The mother becomes pregnant again after a year after the offspring reaches around . She permanently severs her bond with her previous offspring and no longer allows it to suckle, but it remains nearby until it is one-and-a-half to two years old.
Females become sexually mature at about three years of age; in comparison, males reach sexual maturity at about age four although they can experience spermatogenesis as early as two years. Males do not start marking their scent until they reach sexual maturity though their chest glands become functional much earlier. Koalas can breed every year if environmental conditions are good, though the long dependence of the young usually leads to year-long gaps in births.
Koalas can be subject to such as Chlamydiaceae bacteria, which can cause keratoconjunctivitis, urinary tract infection, and reproductive tract infection. Such infections are common on the mainland, but absent in some island populations. , efforts are underway to use vaccination to try to stem the koala chlamydia epidemic. The koala retrovirus (KoRV) may cause koala immune deficiency syndrome (KIDS) which is similar to AIDS in humans. Prevalence of KoRV in koala populations suggests it spread from north to south, for only southern populations have virus-free individuals.
The animals are vulnerable to bushfires due to their slow speed and the flammability of eucalypt trees. The koala instinctively seeks refuge in the higher branches where it is vulnerable to heat and fire. Bushfires divide the animal's habitat, which isolates them, decreases their numbers, and creates genetic bottlenecks. Dehydration and overheating can prove fatal. Consequently, the koala is vulnerable to the effects of climate change. Models of climate change predict warmer and drier climates, suggesting that the koala's range will shrink in the east and south to more .
Botanist Robert Brown was the first to write a formal scientific description in 1803, based on a female specimen captured near what is now Mount Kembla in the Illawarra region of New South Wales. Austrian botanical illustrator Ferdinand Bauer drew the animal's skull, throat, feet, and paws. Brown's work remained unpublished and largely unnoticed, however; his field books and notes remained in his possession until his death, when they were bequeathed to the British Museum in London. They were not identified until 1994, while Bauer's koala watercolours were not published until 1989. William Paterson, who had befriended Brown and Bauer during their stay in New South Wales, wrote an eyewitness report of his encounters with the animals and this would be the basis for British surgeon Everard Home's anatomical writings on them. Home, who in 1808 published his report, coined the scientific name Didelphis coola.
George Perry officially published the first image of the koala in his 1810 natural history work Arcana. Perry called it the "New Holland Sloth", and his dislike for the koala, evident in his description of the animal, was reflected in the contemporary British attitudes towards Australian animals as strange and primitive:
Naturalist and popular artist John Gould illustrated and described the koala in his three-volume work The Mammals of Australia (1845–1863) and introduced the species, as well as other members of Australia's little-known faunal community, to the public. Comparative anatomist Richard Owen, in a series of publications on the physiology and anatomy of Australian mammals, presented a paper on the anatomy of the koala to the Zoological Society of London. In this widely cited publication, he provided an early description of its internal anatomy, and noted its general structural similarity to the wombat. English naturalist George Robert Waterhouse, curator of the Zoological Society of London, was the first to correctly classify the koala as a marsupial in the 1840s, and compared it to fossil species Diprotodon and Nototherium, which had been discovered just recently. Similarly, Gerard Krefft, curator of the Australian Museum in Sydney, noted evolutionary mechanisms at work when comparing the koala to fossil marsupials in his 1871 The Mammals of Australia.
Britain received its first living koala in 1881, which was obtained by the Zoological Society of London. As related by prosecutor to the society, William Alexander Forbes, the animal suffered an accidental demise when the heavy lid of a washstand fell on it and it was unable to free itself. Forbes dissected the specimen and wrote about the female reproductive system, the brain, and the liver—parts not previously described by Owen, who had access only to preserved specimens. Scottish Embryology William Caldwell—well known in scientific circles for determining the reproductive mechanism of the platypus—described the uterine development of the koala in 1884, and used this new information to convincingly map out the evolutionary timeline of the koala and the .
The koala features in the Dreamtime stories and mythology of Indigenous Australians. The Tharawal people believed that the animal helped them get to Australia by rowing the boat. Another myth tells of a tribe that killed a koala and used its long intestines to create a bridge for people from other parts of the world. How the koala lost its tail is the subject of many tales. In one, a kangaroo cuts it off to punish the koala for uncouth behaviour. Tribes in Queensland and Victoria regarded the koala as a wise animal that gave valuable guidance. Bidjara language-speaking people credited the koala for making trees grow in their arid lands. The animal is depicted in rock carvings, though less so than some other species.
Early European settlers in Australia considered the koala to be a creeping sloth-like animal with a "fierce and menacing look". At the turn of the 20th century, the koala's reputation took a positive turn. It appears in Ethel Pedley's 1899 book Dot and the Kangaroo, as the "funny native bear". Artist Norman Lindsay depicted a more anthropomorphic koala in The Bulletin cartoons, starting in 1904. This character also appeared as Bunyip Bluegum in Lindsay's 1918 book The Magic Pudding. The most well known fictional koala is Blinky Bill. Created by Dorothy Wall in 1933, the character appeared in books, films, TV series, merchandise, and a 1986 environmental song by John Williamson. The koala first appeared on an Australian stamp in 1930.
The song "Ode to a Koala Bear" appears on the B-side of the 1983 Paul McCartney/Michael Jackson duet single "Say Say Say". A koala is the main character in animated cartoons in the early 1980s: Hanna-Barbera's The Kwicky Koala Show and Nippon Animation's Noozles. Food products shaped like the koala include the Caramello Koala chocolate bar and the bite-sized cookie snack Koala's March. Dadswells Bridge in Victoria features a tourist complex shaped like a giant koala and the Queensland Reds rugby team has a koala as its icon.
Australian policymakers declined a 2009 proposal to include the koala in the Environment Protection and Biodiversity Conservation Act 1999. A 2017 WWF report found a 53% decline per generation in Queensland, and a 26% decline in New South Wales. The koala population in South Australia and Victoria appear to be abundant; however, the Australian Koala Foundation (AKF) argued that the exclusion of Victorian populations from protective measures was based on a misconception that the total population was 200,000, whereas they believed in 2012 that it was probably less than 100,000. AKF estimated in 2022 that there could be 43,000–100,000. This compares with 8 to 10 million at the start of the 20th century. The Australian Government's Threatened Species Scientific Committee estimated that the 2021 koala population was 92,000, down from 185,000 two decades prior.
The koala was heavily hunted by European settlers in the early 20th century, largely for its fur. Australia exported as many as two million pelts by 1924. Koala furs were used to make rugs, coat linings, muffs, and on women's garment trimmings. The first successful efforts at conserving the species were initiated by the establishment of Brisbane's Lone Pine Koala Sanctuary and Sydney's Koala Park Sanctuary in the 1920s and 1930s. Its owner Noel Burnet created the first successful breeding program.
One of the biggest threats to the koala is habitat destruction and fragmentation. Near the coast, the main cause of this is urbanisation, while in rural areas, habitat is cleared for agriculture. Its favoured trees are harvested for wood products. In 2000, Australia had the fifth highest rate of land clearance globally, stripping of native plants. The koalas' distribution has shrunk by more than 50% since European arrival, largely due to habitat fragmentation in Queensland. Nevertheless, koalas live in many protected areas.
While urbanisation can pose a threat to koala populations, the animals can survive in urban areas given enough trees. Urban populations have distinct vulnerabilities: collisions with vehicles and attacks by domestic dogs. Cars and dogs kill about 4,000 animals every year. To reduce road deaths, government agencies have been exploring various wildlife crossing options, such as the use of fencing to channel animals toward an underpass, in some cases adding a walkway to an existing culvert. Injured koalas are often taken to wildlife hospitals and rehabilitation centres. In a 30-year retrospective study performed at a New South Wales koala rehabilitation centre, trauma was found to be the most frequent cause of admission, followed by symptoms of Chlamydia infection.
Distribution and habitat
Behaviour and ecology
Foraging and activities
Social life
Reproduction and development
Health and mortality
Relation to humans
History
... the eye is placed like that of the Sloth, very close to the mouth and nose, which gives it a clumsy awkward appearance, and void of elegance in the combination ... they have little either in their character or appearance to interest the Naturalist or Philosopher. As Nature however provides nothing in vain, we may suppose that even these torpid, senseless creatures are wisely intended to fill up one of the great links of the chain of animated nature ...
Cultural significance
Koala diplomacy
Conservation
See also
External links
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