Koala

Adopted by white settlers, "koala" became one of several hundred Aboriginal loan words in Australian English, where it was also commonly referred to as "native bear",^[5] later "koala bear", for its supposed resemblance to a bear.^[6] It is also one of several Aboriginal words that made it into International English alongside words like "didgeridoo" and "kangaroo".^[6] The generic name, Phascolarctos, is derived from the Greek words φάσκωλος (phaskolos) 'pouch' and ἄρκτος (arktos) 'bear'. The specific name, cinereus, is Latin for 'ash coloured'.^[7]

Taxonomy

The koala was given its generic name Phascolarctos in 1816 by French zoologist

The koala is classified with wombats (family Vombatidae) and several extinct families (including marsupial tapirs, marsupial lions and giant wombats) in the suborder Vombatiformes within the order Diprotodontia.^[10] The Vombatiformes are a sister group to a clade that includes macropods (kangaroos and wallabies) and possums.^[11] The koala's lineage possibly branched off around 40 million years ago during the Eocene.^[12]

The modern koala is the only

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 questions this hypothesis, noting that P. cinereus and P. stirtoni were sympatric during the middle to late Pleistocene, and the major difference in the morphology of their teeth.^[17] The fossil record of the modern koala extends back at least to the middle Pleistocene.^[18]

Genetics and variations

Three

Other studies have found that koala populations have high levels of inbreeding and low genetic variation.^[23][24] Such low genetic diversity may have been caused by declines in the population during the late Pleistocene.^[25] Rivers and roads have been shown to limit gene flow and contribute to the isolation of southeast Queensland populations.^[26] In April 2013, scientists from the Australian Museum and Queensland University of Technology announced they had fully sequenced the koala genome.^[27]

Characteristics

The koala is a robust animal with a large head and vestigial or non-existent tail.^{[9]: 1 [28]} It has a body length of 60–85 cm (24–33 in) and a weight of 4–15 kg (9–33 lb),^[28] making it among the largest arboreal marsupials.^[29] Koalas from Victoria are twice as heavy as those from Queensland.^[21]: 7 The species is sexually dimorphic, with males 50% larger than females. Males are further distinguished from females by their more curved noses^[29] and the presence of chest glands, which are visible as bald patches.^[21]: 55 The female's pouch opening is secured by a sphincter which holds the young in.^[30]

The pelage of the koala is denser on the back.

For a mammal, the koala has a

The koala's geographic range covers roughly 1,000,000 km² (390,000 sq mi), and 30 ecoregions.^[39] It ranges throughout mainland eastern and southeastern Australia, including the states of Queensland, New South Wales, Victoria, and South Australia. The koala was also introduced to several nearby islands.^[1] The population on Magnetic Island represents the northern limit of its range.^[39]

Fossil evidence shows that the koala's range stretched as far west as southwestern

Koalas are

Due to their low-energy diet, koalas limit their activity and sleep 20 hours a day.[9]^{: 93 [44]} 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.^[21]: 39 On warm days, a koala may rest with its back against a branch or lie down with its limbs dangling.^{[9]: 93–94} When it gets very hot, the koala rests lower in the canopy and near the trunk, where the surface is cooler than the surrounding air.^[45] It curls up when it gets cold and wet.^[21]: 39 A koala will find a lower, thicker branch on which to rest when it gets windy. 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.^{[9]: 93–94} The koala usually grooms itself with its hind paws, with their double claws, but sometimes uses its forepaws or mouth.^{[9]: 97–98}

Social life

Resting

A bellowing male in the Lone Pine Koala Sanctuary

Koalas are asocial animals and spend just 15 minutes a day on social behaviours. Where there are more koalas and fewer trees,

Adult males communicate with loud bellows — "a long series of deep, snoring inhalations and belching exhalations".^[49] Because of their low frequency, these bellows can travel far through the forest.^[21]: 56 Koalas may bellow at any time of the year, particularly during the breeding season, when it serves to attract females and possibly intimidate other males.^[50] They also bellow to advertise their presence to their neighbours when they climb a different tree.^[21]: 57 These sounds signal the male's actual body size, as well as exaggerate it;^[51] females pay more attention to bellows that originate from larger males.^[52] 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.^[49] Squeaking and sqawking are produced when distraught; the former is made by younger animals and the latter by older ones. When another individual climbs over it, a koala makes a low closed-mouth grunt.^{[9]: 102–03 [49]} 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.^{[9]: 104–05}

Agonistic behaviour typically consists of quarrels between individuals that are trying to pass each other in the tree. This occasionally involves biting. Strangers may wrestle, chase, and bite each other.^{[9]: 102 [53]} In extreme situations, a 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.^{[9]: 101–02} Pregnant and lactating females are particularly aggressive and attack individuals that come too close.^[53] In general, however, koalas tend to avoid fighting due to energy costs.^[2]: 191

Reproduction and development

Koalas are seasonal breeders, and give birth from October to May. Females in

The joey latches on to one of the female's two teats and suckles it.[21]^: 61 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 in the pouch.^[21]: 62 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 50 g (1.8 oz) and its head is twice as big as before. 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.^[21]: 63

At six or seven months of age, the joey weighs 300–500 g (11–18 oz) and fully emerges from the pouch for the first time. It explores its new surroundings cautiously, clutching its mother for support.^[21]: 65 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.^[56] A nine month old joey has its adult coat colour and weighs 1 kg (2.2 lb). Having permanently left the pouch, it rides on its mother's back for transportation, learning to climb by grasping branches.^{[21]: 65–66} Gradually, it becomes more independent from its mother, who becomes pregnant again after a year, and the young is now around 2.5 kg (5.5 lb). Her bond with her previous offspring is permanently severed and she no longer allows it to suckle, but it will stay nearby until it is one-and-a-half to two years old.^{[21]: 66–67}

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,^[57] although they can experience spermatogenesis as early as two years.^[21]: 68 Males do not start marking their scent until they reach sexual maturity, though their chest glands become functional much earlier.^[48] 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.^[16]: 236

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 risky lives.