|The koala is a completely arboreal marsupial native to Australia. This folivorous herbivore has a specialized diet and relies on eucalyptus for its food and water requirements. Because of its poor diet, the koala is mostly sedentary and sleeps most of the day in trees.|
Koalas exhibit sexual dimorphism with the males being larger. Males are up to 50% heavier than females, have a broader face, somewhat smaller ears, and a large chest gland.
Female koalas have two mammae; and rather than a chest gland, have a pouch that opens to the rear and extends upward and forward.
Koalas from the southern end of the range are generally larger in size than their northern counterparts and have coats that are generally longer and darker. In the south, males have an average head-body length of 78 centimeters and an average weight of 11.8 kilograms, while females have an average head-body length of 72 centimeters and an average weight of 7.9 kilograms. In the north, males average 6.5 kilograms and females 5.1 kilograms.
Koalas have dense, wooly fur that is gray to brown on top and varies with geographic location. There is white on the chin, chest, and inner side of the forelimbs. The rump is often dappled with white patches and the ears are fringed with long, white hairs.
The koala’s coat is generally shorter and lighter in the north of range.
Koalas have a vestigial tail.
The koala’s paws are large, and both fore and hind feet have five strongly clawed digits. On the forepaw the first and second digits oppose the other three which enables the koala to grip branches as it climbs. The first digit of the hind foot is short and greatly broadened while the second and third digits are relatively small and partly syndactylous but have separate claws.
Koalas may live past 10 years in the wild, and there have been reports of lifespans over 20 years in captivity. In the wild, longevity of 12 for males to 15 years for females has been reported.
Generation length is 6-8 years.
P. c. adustus (Northern Queensland)
P. c. cinereus (New South Wales)
P. c. victor (Victoria)
The word koala comes from the Dharug gula, meaning no water.
It was at one time thought, since the animals were not observed to come down from trees often, that they were able to survive without drinking. The leaves of the eucalyptus tree have a high water content, so the koala does not need to drink often. But the notion that they do not need to drink water at all was shown to be a myth.
Although the vowel u was originally written in the English orthography as oo (in spellings such as coola or koolah), it was changed to oa, possibly in error.
Adopted by white settlers, koala became one of several hundred Aboriginal loan words in Australian English, where it has also commonly been used in the alternative form koala bear, because of the koala’s supposed resemblance to a bear. It is also one of several Aboriginal words that made it into International English, alongside didgeridoo and kangaroo.
Koalas are commonly called an alternative name of koala bear because of the koala’s supposed resemblance to a bear.
The koala’s scientific name is Phascolarctos cinereus. The generic name, Phascolarctos, is derived from the Greek words phaskolos and arktos. Phaskolos translates to pouch, referring to the female koala’s pouch that opens to the rear and extends upward and forward, and arktos translates to bear, again remarking the koala’s resemblance to species in the Ursidae family. The specific name, cinereus, is Latin for ash-colored.
Despite being commonly called “koala bear”, koalas are not bears and are instead marsupials found in the Diprotodontia order with the scientific name of Phascolarctos cinereus.
Traditionally, three distinct koala 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 and their boundaries are based on state borders.
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 status of koala 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.
The koala is endemic to Australia and lives in the eastern range from northern Queensland to southwestern Victoria.
The koala was formerly common throughout the broad band of forests and woodlands dominated by Eucalyptus spp. extending from north Queensland to the south-eastern corner of mainland South
Currently, the koala occurs in northeastern, central, and southeastern Queensland with patchy populations in western areas; eastern New South Wales including the coastal strip and highlands of the Great Dividing Range, as well as the western plains and related riparian environments where suitable habitat occurs; Victoria; and southeastern South Australia.
Koalas inhabit temperate and subtropical/tropical dry forests and dry savanna habitats.
The koala occurs in forests and woodlands, typically dominated by eucalyptus species. In inland, semi-arid portions of its range, it occurs mainly in riparian woodlands. Elsewhere, distribution may be associated particularly with soil fertility and hence foliage nutrient content.
They are confined to eucalyptus forests below 600 meters.
Koalas are completely arboreal, remaining mostly in the branches of eucalyptus trees where they are able to feed and stay out of reach of their predators. Koalas come to the ground occasionally to move to another food tree or to lick up soil or gravel which aids in digestion.
Because the koala has no sweat glands, it cools itself by licking its arms and stretching out as it rests in the trees.
Koalas are mainly nocturnal and feed at night. During the breeding season in October-February, adult males are very active at night and move constantly through their range, both ejecting male rivals and mating with any receptive females.
Because of their low-quality diet, koalas conserve energy by their relatively sedentary behavior. They are slow-moving and sleep up to 18 hours a day. Because koalas are extremely slow-moving animals, they are relatively defenseless.
The koala is primarily a solitary animal and outside of the breeding season, there is little obvious social behavior. Koalas live in loose-knit groups if enough suitable trees are present, but only one animal per tree. Sometimes, koalas lives in small harems led by a single male.
Individual adult koalas occupy fixed home ranges that have extensive overlap. Koala home range size varies substantially with forest structure and productivity, and males typically have larger home ranges than females. In a coastal forest in New South Wales, average home range size was 10 hectares for females to 20 hectares for males. In inland Queensland, home ranges were 100 hectares for females to 135 hectares for male. For breeding males, the home range will overlap those of females as well as sub-adult and non-breeding males.
Koalas are herbivorous and folivorous, feeding on both eucalypt and non-eucalypt species.
Koalas have a highly specialized diet in which they eat only 20 of the 350 species of eucalyptus and prefer only 5 species. The koala’s diet is mostly limited to foliage of Eucalyptus species with occasional intake of leaves of other plants, mostly in the Myrtaceous genera, but the bulk of its diet comes from only a few eucalypt species. Eucalyptus viminalis and Eucalyptus ovata are preferred in the south, while Eucalyptus punctata, Eucalyptus camaldulensis and Eucalyptus tereticornis are the taste of the north.
The leaves that koalas feast on are highly toxic, but koalas have a flora of bacteria in their stomachs that metabolize the toxins of the leaves.
The koala has adapted to cope with its high-fiber, low-protein diet. The cheek teeth are reduced to a single premolar and four broad, highly cusped molars on each jaw which finely grind the leaves for easier digestion. In addition, the koala’s caecum is up to four times its body size. The koala also has cheek pouches that allow the animal to store unchewed food while moving to a safer or more protected location.
An adult koala can eat 500 grams daily.
Koalas are polygynous and breed seasonally. During the breeding season in October-Febraury, adult males are very active at night and move constantly through their range, both ejecting male rivals and mating with any receptive females.
Female koalas are sexually mature at two years of age. Males are fertile at two years but usually don’t mate until they reach four simply because competition for females requires a larger size.
During the breeding season, male koalas use loud, bellowing calls that consist of a series of harsh inhalations each followed by a resonant, growling expiration. These calls advertise an individual’s presence and warn off other males. The only vocalization generally heard from females and sub-adult males is a harsh, wailing distress call given when harassed by adult males.
Koala copulation is brief, generally lasting less than two minutes, and occurs in a tree. During mating, the male will grasp the back of the female’s neck with his teeth.
Female koalas are seasonally polyestrous, with an estrous cycle of about 27-30 days. Females can produce young at annual intervals and usually breed once every year. Births per adult female per year average 0.3-0.8. The gestation period is 25-35 days with births occurring in mid-summer of December and January, ranging from October to May. Litters generally consist of only one young, but twins have been reported.
Young koalas weigh less than 0.5 grams when born and attach to one of the nipples in the pouch. They have a pouch life of 5-7 months, feeding on milk or predigested leaves that are nontoxic, and are weaned at 6-12 months. Toward the end of their pouch life, the young feed regularly on material passed through the mother’s digestive tract. Once the young begins to feed on leaves, growth is rapid. The young leaves the pouch after seven months and is carried about on the mother’s back. By 11 months of age, the young is independent but may continue to live close to the mother for a few months.
The koala is evaluated as “Vulnerable” on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List of Threatened Species. The IUCN considers that the conservation status of the koala is border-line between Near Threatened and Vulnerable, but adopts a precautionary assessment given the proximity of the estimated current and projected rate of decline to the threshold, and published assessments of the likelihood of additional and compound impacts due to climate change.
The koala holds no special status, although the Environment Australia Biodiversity Group calls the koala lower risk-near threatened.
The conservation status of the koala has been contested, in part because of uncertainty about relevant population parameters and marked variation in population trends across its large range.
The koala’s total geographic range and overall distribution has contracted significantly due to loss of large areas of habitat since European settlement. This decline was primarily due to disease, bushfires, and widespread habitat destruction in the early decades of the 20th century. In Queensland, extent of occurrence and area of occupancy have contracted by about 30%.
In 2012, the overall rate of decline in population size over the last 18-24 years, or three generations, was estimated at about 28% by the Threatened Species Scientific Committee. This rate is substantially influenced by a severe decline in inland regions most exposed to recent drought.
A separate expert elicitation process involving independent estimates from 15 koala experts of population size in every bioregion inhabited by koalas concluded that the koala population size reduction or projected reduction over three generations is a mean of 29%, albeit with substantial variation amongst experts in estimation of this rate.
Climate change is expected to lead to an increased rate of population reduction over the next 20-30 years, and the impacts of other threats will magnify over this period.
Public concern for the koala is high and there are management problems with many populations. Remnant populations living at high densities in isolated patches of habitat are at greatest risk. Effective management of some of the koala’s threats on the mainland could lead to excessive abundance and result in pest problems similar to those occurring on Kangaroo Island and in parts of Victoria.
At high population densities, koalas can defoliate preferred tree species, causing tree death and subsequent koala population crash. As such, management of the koala can be difficult.
Populations that are protected can reach such high numbers in an area that they destroy the trees on which they feed. Often portions of populations have to be relocated in order to reduce the number of individuals in a given area. However, this is complicated by the shortage of suitable forest areas where surplus animals can be released.
Current threats to the koala include continued habitat destruction, fragmentation, and modification (which makes them vulnerable to predation by dogs, vehicle strikes, and other factors), bushfires, and disease, as well as drought-associated mortality in habitat fragments. Koalas are also threatened by the microorganism Chlamydia psittaci, which can make them sterile.
Currently, the koala’s main threat is habitat destruction.
Climate change is likely to have severe consequences for the koala. Climate change is expected to lead to an increased rate of population reduction over the next 20-30 years, and the impacts of other threats will magnify over this period.
There is no national recovery plan for the koala; however there is a national conservation and management strategy, a recovery plan in New South Wales, a management strategy in Victoria, and a conservation plan and management program in Queensland.
A recent parliamentary inquiry concluded that the national conservation and management strategy was largely ineffective.
In part because of its iconic status, there has been a relatively long history of conservation management directed specifically at the koala. This has included a substantial history of translocations, including conservation marooning and re-introduction, mostly in Victoria, and introduction, mostly in South Australia, some land management and forestry prescriptions, monitoring, substantial research, and localized management of some threats.
There are numerous captive breeding facilities in Australia, and internationally.