The koala (Phascolarctos cinereus, or, inaccurately, koala bear) is an arboreal herbivorous marsupial native to Australia. It is the only extant representative of the family Phascolarctidae and its closest living relatives are the wombats. The koala is found in coastal areas of the mainland’s eastern and southern regions, inhabiting Queensland, New South Wales, Victoria, and South Australia. It is easily recognizable by its stout, tailless body and large head with round, fluffy ears and large, spoon-shaped nose. The koala has a body length of 60-85 cm (24-33 in) and weighs 4-15 kg (9-33 lb). Pelage color ranges from silver grey to chocolate brown. Koalas from the northern populations are typically smaller and lighter in color than their counterparts further south. These populations possibly are separate subspecies, but this is disputed.
Koalas typically inhabit open eucalyptus woodlands, and the leaves of these trees make up most of their diet. Because this eucalypt diet has limited nutritional and caloric content, koalas are largely sedentary and sleep up to 20 hours a day. They are asocial animals, and bonding exists only between mothers and dependent offspring. Adult males communicate with loud bellows that intimidate rivals and attract mates. Males mark their presence with secretions from scent glands located on their chests. Being marsupials, koalas give birth to underdeveloped young that crawl into their mothers’ pouches, where they stay for the first six to seven months of their lives. These young koalas, known as joeys, are fully weaned around a year old. Koalas have few natural predators and parasites, but are threatened by various pathogens, such as Chlamydiaceae bacteria and the koala retrovirus, as well as by bush fires and droughts.
Koalas 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Botanist Robert Brown wrote the first detailed scientific description of the koala in 1814, although his work remained unpublished for 180 years. Popular artist John Gould illustrated and described the koala, introducing the species to the general British public. Further details about the animal’s biology were revealed in the 19th century by several English scientists. Because of its distinctive appearance, the koala is recognized worldwide as a symbol of Australia. Koalas are listed as Vulnerable by the International Union for Conservation of Nature. The Australian government similarly lists specific populations in Queensland and New South Wales as Vulnerable. The animal was hunted heavily in the early 20th century for its fur, and large-scale cullings in Queensland resulted in a public outcry that initiated a movement to protect the species. Sanctuaries were established, and translocation efforts moved to new regions koalas whose habitat had become fragmented or reduced. The biggest threat to their existence is habitat destruction caused by agriculture and urbanization.
Genetics and variations
Traditionally, three distinct subspecies have been recognized: the Queensland koala (P. c. adustus, Thomas 1923), the New South Wales koala (P. c. cinereus, Goldfuss 1817), and the Victorian koala (P. c. victor, Troughton 1935). These forms are distinguished by pelage color and thickness, body size, and skull shape. The Queensland koala is the smallest of the three, with shorter, silver fur and a shorter skull. The Victorian koala is the largest, with shaggier, brown fur and a wider skull. The boundaries of these variations are based on state borders, and their status as subspecies is disputed. A 1999 genetic study suggests that the variations represent differentiated populations with limited gene flow between them, and that the three subspecies comprise a single evolutionarily significant unit. Other studies have found that koala populations have high levels of inbreeding and low genetic variation. Such low genetic diversity may have been a characteristic of koala populations since the late Pleistocene. Rivers and roads have been shown to limit gene flow and contribute to the genetic differentiation 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.
Ecology and behavior
The koala’s geographic range covers roughly 1,000,000 km2 (390,000 sq mi), and 30 ecoregions. It extends throughout eastern and southeastern Australia, encompassing northeastern, central and southeastern Queensland, eastern New South Wales, Victoria, and southeastern South Australia. The koala was introduced near Adelaide and on several islands, including Kangaroo Island and French Island. The population on Magnetic Island represents the northern limit of its range. 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.
In Queensland, koalas are unevenly distributed and uncommon except in the southeast, where they are numerous. In New South Wales, they are abundant only in Pilliga, while in Victoria they are common nearly everywhere. In South Australia, koalas were extirpated by 1920 and subsequently reintroduced. Koalas can be found in habitats ranging from relatively open forests to woodlands, and in climates ranging from tropical to cool temperate. In semi-arid climates, they prefer riparian habitats, where nearby streams and creeks provide refuge during times of drought and extreme heat.
Foraging and activities
Koalas are herbivorous, and while most of their diet consists of eucalyptus leaves, they can be found in trees of other genera, such as Acacia, Allocasuarina, Callitris, Leptospermum, and Melaleuca. Although the foliage of over 600 species of Eucalyptus is available, the koala shows a strong preference for around 30. They tend to choose species that have a high protein content and low proportions of fibre and lignin. The most favored species are Eucalyptus microcorys, E. tereticornis, and E. camaldulensis, which, on average, make up more than 20% of their diet. Despite its reputation as a fussy eater, the koala is more generalist than some other marsupial species, such as the greater glider. Since eucalyptus leaves have a high water content, the koala does not need to drink often; its daily water turnover rate ranges from 71 to 91 ml/kg of body weight. Although females can meet their water requirements from eating leaves, larger males require additional water found on the ground or in tree hollows. When feeding, a koala holds onto a branch with hindpaws and one forepaw while the other forepaw grasps foliage. Small koalas can move close to the end of a branch, but larger ones stay near the thicker bases. Koalas consume up to 400 grams (14 oz) of leaves a day, spread over four to six feeding sessions. Despite their adaptations to a low-energy lifestyle, they have meager fat reserves and need to feed often.
Because they get so little energy from their diet, koalas must limit their energy use and sleep 20 hours a day; only 4 hours a day are spent in active movement. They are predominantly active at night and spend most of their waking hours feeding. They typically eat and sleep in the same tree, possibly for as long as a day. On very hot days, a koala may climb down to the coolest part of the tree which is cooler than the surrounding air. The koala hugs the tree to lose heat without panting. On warm days, a koala may rest with its back against a branch or lie on its stomach or back with its limbs dangling. During cold, wet periods, it curls itself into a tight ball to conserve energy. On windy days, a koala finds a lower, thicker branch on which to rest. While it spends most of the time in the tree, the animal descends to the ground to move to another tree, walking on all fours. The koala usually grooms itself with its hindpaws, but sometimes uses its forepaws or mouth
Koalas are seasonal breeders, and births take place from the middle of spring through the summer to early autumn, from October to May. Females in oestrus tend to hold their heads further back than usual and commonly display tremors and spasms. However, males do not appear to recognize these signs, and have been observed to mount non-oestrous females. Because of his much larger size, a male can usually force himself on a female, mounting her from behind, and in extreme cases, the male may pull the female out of the tree. A female may scream and vigorously fight off her suitors, but will submit to one that is dominant or is more familiar. The bellows and screams that accompany matings can attract other males to the scene, obliging the incumbent to delay mating and fight off the intruders. These fights may allow the female to assess which is dominant. Older males usually have accumulated scratches, scars, and cuts on the exposed parts of their noses and on their eyelids.
The koala’s gestation period lasts 33-35 days, and a female gives birth to a single joey (although twins occur on occasion). As with all marsupials, the young are born while at the embryonic stage, weighing only 0.5 g (0.02 oz). However, they have relatively well-developed lips, forelimbs, and shoulders, as well as functioning respiratory, digestive, and urinary systems. The joey crawls into its mother’s pouch to continue the rest of its development. Unlike most other marsupials, the koala does not clean her pouch.
A female koala has two teats; the joey attaches itself to one of them and suckles for the rest of its pouch life. The koala has one of the lowest milk energy production rates in relation to body size of any mammal. The female makes up for this by lactating for as long as 12 months. At seven weeks of age, the joey’s head grows longer and becomes proportionally large, pigmentation begins to develop, and its sex can be determined (the scrotum appears in males and the pouch begins to develop in females). At 13 weeks, the joey weighs around 50 g (1.8 oz) and its head has doubled in size. The eyes begin to open and fine fur grows on the forehead, nape, shoulders, and arms. At 26 weeks, the fully furred animal resembles an adult, and begins to poke its head out of the pouch.
As the young koala approaches six months, the mother begins to prepare it for its eucalyptus diet by predigesting the leaves, producing a faecal pap that the joey eats from her cloacum. The pap is quite different in composition from regular faeces, resembling instead the contents of the caecum, which has a high concentration of bacteria. Eaten for about a month, the pap provides a supplementary source of protein at a transition time from a milk to a leaf diet. The joey fully emerges from the pouch for the first time at six or seven months of age, when it weighs 300-500 g (11-18 oz). It explores its new surroundings cautiously, clinging to its mother for support. By nine months, it weighs over 1 kg (2.2 lb) and develops its adult fur color. Having permanently left the pouch, it rides on its mother’s back for transportation, learning to climb by grasping branches. Gradually, it spends more time away from its mother, and at 12 months it is fully weaned, weighing around 2.5 kg (5.5 lb). When the mother becomes pregnant again, her bond with her previous offspring is permanently severed. Newly weaned young are encouraged to disperse by their mothers’ aggressive behavior towards them.
Females become sexually mature at about three years of age and can then become pregnant; in comparison, males reach sexual maturity when they are about four years old, although they can produce sperm as early as two years. While the chest glands can be functional as early as 18 months of age, males do not begin scent-marking behaviors until they reach sexual maturity. Because the offspring have a long dependent period, female koalas usually breed in alternate years. Favorable environmental factors, such as a plentiful supply of high-quality food trees, allow them to reproduce every year.
Health and mortality
Koalas may live from 13 to 18 years in the wild. While female koalas usually live this long, males may die sooner because of their more hazardous lives. Koalas usually survive falls from trees and immediately climb back up, but injuries and deaths from falls do occur, particularly in inexperienced young and fighting males. Around six years of age, the koala’s chewing teeth begin to wear down and their chewing efficiency decreases. Eventually, the cusps disappear completely and the animal will die of starvation.
Koalas have few predators; dingos and large pythons may prey on them, while birds of prey (such as powerful owls and wedge-tailed eagles) are threats to young. They are generally not subject to external parasites, other than ticks in coastal areas. Koalas may also suffer mange from the mite Sarcoptes scabiei, and skin ulcers from the bacterium Mycobacterium ulcerans, but neither is common. Internal parasites are few and largely harmless. These include the tapeworm Bertiella obesa, commonly found in the intestine, and the nematodes Marsupostrongylus longilarvatus and Durikainema phascolarcti, which are infrequently found in the lungs. In a three-year study of almost 600 koalas admitted to the Australian Zoo Wildlife Hospital in Queensland, 73.8% of the animals were infected with at least one species of the parasitic protozoal genus Trypanosoma, the most common of which was T. irwini.
Koalas can be subject to pathogens such as Chlamydiaceae bacteria, which can cause keratoconjunctivitis, urinary tract infection, and reproductive tract infection. Such infections are widespread on the mainland, but absent in some island populations. 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 a trend spreading from the north to the south of Australia. Northern populations are completely infected, while some southern populations (including Kangaroo Island) are free.
The animals are vulnerable to bush fires due to their slow movements and the flammability of eucalyptus trees. The koala instinctively seeks refuge in the higher branches, where it is vulnerable to intense heat and flames. Bush fires also fragment the animal’s habitat, which restricts their movement and leads to population decline and loss of genetic diversity. Dehydration and overheating can also prove fatal. Consequently, the koala is vulnerable to the effects of climate change. Models of climate change in Australia predict warmer and drier climates, suggesting that the koala’s range will shrink in the east and south to more mesic habitats. Droughts also affect the koala’s well-being. For example, a severe drought in 1980 caused many Eucalyptus trees to lose their leaves. Subsequently, 63% of the population in southwestern Queensland died, especially young animals that were excluded from prime feeding sites by older, dominant koalas, and recovery of the population was slow. Later, this population declined from an estimated mean population of 59,000 in 1995 to 11,600 in 2009, a reduction attributed largely to hotter and drier conditions resulting from droughts in most years between 2002 and 2007. Another predicted negative outcome of climate change is the effect of elevations in atmospheric CO2 levels on the koala’s food supply: increases in CO2 cause Eucalyptus trees to reduce protein and increase tannin concentrations in their leaves, reducing the quality of the food source.
While the koala was previously classified as Least Concern on the Red List, it was uplisted to Vulnerable in 2016. Australian policy makers declined a 2009 proposal to include the koala in the Environment Protection and Biodiversity Conservation Act 1999. In 2012, the Australian government listed koala populations in Queensland and New South Wales as Vulnerable, because of a 40% population decline in the former and a 33% decline in the latter. Populations in Victoria and South Australia appear to be abundant; however, the Australian Koala Foundation argues that the exclusion of Victorian populations from protective measures is based on a misconception that the total koala population is 200,000, whereas they believe it is probably less than 100,000.
Koalas were hunted for food by Aboriginals. A common technique used to capture the animals was to attach a loop of ropey bark to the end of a long, thin pole, so as to form a noose. This would be used to snare an animal high in a tree, beyond the reach of a climbing hunter; an animal brought down this way would then be killed with a stone hand axe or hunting stick (waddy). According to the customs of some tribes, it was considered taboo to skin the animal, while other tribes thought the animal’s head had a special status, and saved them for burial.
The koala was heavily hunted by European settlers in the early 20th century, largely for its thick, soft fur. More than two million pelts are estimated to have left Australia by 1924. Pelts were in demand for use in rugs, coat linings, muffs, and as trimming on women’s garments. Extensive cullings occurred in Queensland in 1915, 1917, and again in 1919, when over one million koalas were killed with guns, poisons, and nooses. The public outcry over these cullings was probably the first wide-scale environmental issue that rallied Australians. Novelist and social critic Vance Palmer, writing in a letter to The Courier-Mail, expressed the popular sentiment:
“The shooting of our harmless and lovable native bear is nothing less than barbarous … No one has ever accused him of spoiling the farmer’s wheat, eating the squatter’s grass, or even the spreading of the prickly pear. There is no social vice that can be put down to his account … He affords no sport to the gun-man … And he has been almost blotted out already from some areas.”
Despite the growing movement to protect native species, the poverty brought about by the drought of 1926-28 led to the killing of another 600,000 koalas during a one-month open season in August 1927. In 1934, Frederick Lewis, the Chief Inspector of Game in Victoria, said that the once-abundant animal had been brought to near extinction in that state, suggesting that only 500-1000 remained.
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. The owner of the latter park, Noel Burnet, became the first to successfully breed koalas and earned a reputation as the foremost contemporary authority on the marsupial. In 1934, David Fleay, curator of Australian mammals at the Melbourne Zoo, established the first Australian faunal enclosure at an Australian zoo, and featured the koala. This arrangement allowed him to undertake a detailed study of its diet in captivity. Fleay later continued his conservation efforts at Healesville Sanctuary and the David Fleay Wildlife Park.
Since 1870, koalas have been introduced to several coastal and offshore islands, including Kangaroo Island and French Island. Their numbers have significantly increased, and since the islands are not large enough to sustain such high koala numbers, overbrowsing has become a problem. In the 1920s, Lewis initiated a program of large-scale relocation and rehabilitation programs to transfer koalas whose habitat had become fragmented or reduced to new regions, with the intent of eventually returning them to their former range. For example, in 1930-31, 165 koalas were translocated to Quail Island. After a period of population growth, and subsequent overbrowsing of gum trees on the island, about 1,300 animals were released into mainland areas in 1944. The practice of translocating koalas became commonplace; Victorian State manager Peter Menkorst estimated that from 1923 to 2006, about 25,000 animals were translocated to more than 250 release sites across Victoria. Since the 1990s, government agencies have tried to control their numbers by culling, but public and international outcry has forced the use of translocation and sterilization, instead.
One of the biggest anthropogenic threats to the koala is habitat destruction and fragmentation. In coastal areas, the main cause of this is urbanization, while in rural areas, habitat is cleared for agriculture. Native forest trees are also taken down to be made into wood products. In 2000, Australia ranked fifth in the world by deforestation rates, having cleared 564,800 hectares (1,396,000 acres). The distribution of the koala has shrunk by more than 50% since European arrival, largely due to fragmentation of habitat in Queensland. The koala’s “vulnerable” status in Queensland and New South Wales means that developers in these states must consider the impacts on this species when making building applications. In addition, koalas live in many protected areas.
While urbanization can pose a threat to koala populations, the animals can survive in urban areas provided enough trees are present. Urban populations have distinct vulnerabilities: collisions with vehicles and attacks by domestic dogs kill about 4,000 animals every year. Injured koalas are often taken to wildlife hospitals and rehabilitation centers. In a 30-year retrospective study performed at a New South Wales koala rehabilitation center, trauma (usually resulting from a motor vehicle accident or dog attack) was found to be the most frequent cause of admission, followed by symptoms of Chlamydia infection. Wildlife caretakers are issued special permits, but must release the animals back into the wild when they are either well enough or, in the case of joeys, old enough. As with most native animals, the koala cannot legally be kept as a pet in Australia or anywhere else.