Koala
The koala is a stocky animal with a large head and vestigial or non-existent tail. It has a body length of 60–85 cm and a weight of 4-15 kg, making it among the largest arboreal marsupials. Koalas from Victoria are twice as heavy as those from Queensland. The species is sexually dimorphic, with males 50% larger than females. Males are further distinguished from females by their more curved noses and the presence of chest glands, which are visible as hairless patches.
Habitat
Their geographic range covers roughly 1,000,000 km2, 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.
Diet
Koalas are herbivorous, and while most of their diet consists of eucalypt leaves. Though 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 are high in protein and low in fibre and lignin. Eucalyptus on average makes 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 eucalypt leaves have a high water content, the koala doesn't need to drink often; its daily water turnover rate ranges from 71-91 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 its 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 g of leaves a day, spread over four to six feeding sessions. Despite their adaptations to a low-energy lifestyle, they have meagre fat reserves and need to feed often. Because they get so little energy from their diet, koalas must limit their energy use and sleep or rest 20 hours a day. They are predominantly active at night and spend most of their waking hours feeding.
Breeding
They 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 recognise 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 (twins occur on occasions). As with all marsupials, the young are born while at the embryonic stage, weighing only 0.5 g. 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 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 cloaca. 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. It explores its new surroundings cautiously, clinging to its mother for support. By nine months, it weighs over 1 kg and develops its adult fur colour. 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. 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 behaviour 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 behaviours until they reach sexual maturity. Because the offspring have a long dependent period, female koalas usually breed in alternate years. Favourable environmental factors, such as a plentiful supply of high-quality food trees, allow them to reproduce every year.
Population
They were previously classified as Least Concern on the Red List, it was uplisted to Vulnerable in 2016. According to the IUCN Red List, they are classed as Vulnerable(V). Their population trend is decreasing and there are about 100,000-500,000 mature individuals. 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.
Threats
Current threats to this species 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. Public concern for the species is high. 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 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. The overall distribution of Koalas has been reduced since European settlement. This decline was primarily due to disease, bushfires, and widespread habitat destruction in the early decades of the 20th century. Commercial harvesting also took place across the range towards the end of the 19th century and early 20th century (large numbers, running into the millions, were killed for their pelts for a large export industry in Victoria, New South Wales, and Queensland). This was banned in Victoria in the 1890s, and it continued sporadically (and under regulation) in Queensland until 1927. There is no evidence, however, that the early spate of commercial harvesting had any long-term impact on the overall population. Climate change is likely to have severe consequences for this species.
Conservation
There is no national recovery plan; however there is a national conservation and management strategy (NRMMC 2009), a recovery plan for the Koala in New South Wales (NSW DECC 2008), a management strategy in Victoria, and a conservation plan and management program for the Koala in Queensland (Queensland EPA 2006). A recent parliamentary inquiry concluded that the national conservation and management strategy was largely ineffective (The Senate Environment and Communications References Committee 2011). 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, Menkhorst 2008) and introduction (mostly in South Australia), some land management and forestry prescriptions, monitoring, substantial research, and localised management of some threats. There are numerous captive breeding facilities in Australia, and internationally.