Koala - CONFIRMED
Phascolarctos cinereus
Summary 2
The koala (Phascolarctos cinereus), sometimes called the 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 recognisable by its stout, tailless body and large head with round, fluffy ears and large, dark nose. The koala has a body length of 60–85 cm (24–33 in) and weighs 4–15 kg (9–33 lb). 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 possibly are separate subspecies, but this is disputed.
Distribution and habitat 3
The koala's geographic range covers roughly 1,000,000 km2 (390,000 sq mi), and 30 ecoregions. 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. 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. Koalas were introduced to Western Australia at Yanchep in 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 riparian habitats, where nearby streams and creeks provide refuge during times of drought and extreme heat.
Characteristics 3
The koala is a robust animal with a large head and vestigial or non-existent tail. It has a body length of 60–85 cm (24–33 in) and a weight of 4–15 kg (9–33 lb), 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 bald patches. The female's pouch opening is secured by a sphincter which holds the young in.
The pelage of the koala is denser on the back. The 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 highly resilient to wind and rain, while the belly fur can reflect solar radiation. The koala's curved, sharp claws are 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 scale trees. In addition, the thigh muscles are anchored further down the shinbone, increasing its climbing power.
For a mammal, the koala has a proportionally small brain, being 60% smaller than that of a typical diprotodont, weighing only 19.2 g (0.68 oz) on average. The brain's surface is fairly smooth and "primitive". It does not entirely fill up the cranial cavity, unlike in most mammals, and is lightened by large amounts of cerebrospinal fluid. It is possible that the fluid protects the brain when animal falls from a tree. The koala's small brain size may be an adaptation to the energy restrictions imposed by its diet, which is insufficient to sustain a larger brain. Because of its small brain, the koala has a limited ability to perform complex, unusual behaviours. For example, it will not eat plucked leaves on a flat surface, which conflicts with its normal 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 down even further. They also 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 poor, toxic and fibrous diet. The animal's dentition consists of the incisors and cheek teeth (a single premolar and four molars on each jaw), which 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 also store food in their cheek pouches before it is ready to be chewed. The partially worn molars of koalas in their prime are optimal for breaking the leaves into small particles, resulting in more efficient stomach digestion and nutrient absorption in the small intestine, which digests the eucalyptus leaves to provide most of the animal's energy. A koala sometimes regurgitates the food into the mouth to be chewed a second time.
Koalas are hindgut fermenters, and their digestive retention can last for up to 100 hours in the wild or up to 200 hours in captivity. This is made possible by their caecum—200 cm (80 in) long and 10 cm (4 in) in diameter—possibly the largest for an animal when accounting for its size. Koalas can hold 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 between seasons and sexes. They can digest the toxic plant secondary metabolites, phenolic compounds and terpenes present in eucalyptus leaves due to their production of cytochrome P450, which breaks down these poisons in the liver. The koala replaces lost water at a lower rate than some other species like some possums. It maintains water by absorbing it in the caecum, resulting in drier faecal pellets packed with undigested fibre.
Behaviour and ecology 3
Koalas are herbivorous, and while most of their diet consists of eucalypt leaves, they can be found in trees of other genera, such as Acacia, Allocasuarina, Callitris, Leptospermum, and Melaleuca. Though the foliage of over 600 species of Eucalyptus is available, the koala shows a strong preference for around 30. They prefer plant matter with higher protein over fibre and lignin. The most favoured 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 picky eater, the koala is more generalist than some other marsupial species, such as the greater glider. The koala does not need to drink often as it can get enough water in the eucalypt leaves, though larger males may additionally drink water found on the ground or in tree hollows. When feeding, a koala reaches out to grab leaves with one forepaw while the other paws hang on to the branch. Depending on the size of the individual, a koala can walk to the end of a branch or must stay near the base. Each day, koalas eat up to 400 grams (14 oz) of leaves, spread over four to six feeding periods. Despite their adaptations to a low-energy lifestyle, they have meagre fat reserves and need to feed often.
Due to their low-energy diet, koalas limit their activity and 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 very 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. 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, leaping along. The koala usually grooms itself with its hind paws, with their double claws, but sometimes uses its forepaws or mouth.
Koalas are asocial animals and spend just 15 minutes a day on social behaviours. Where there are more koalas and fewer trees, home ranges are smaller and more clumped while the reverse is true for areas with fewer animals and more trees. Koala society appears to consist of "residents" and "transients", the former being mostly adult females and the latter males. Resident males appear to be territorial and dominant. The territories of dominant males are found near breeding females, while younger males must wait until they reach full size to challenge for breeding rights. Adult males occasionally venture outside their home ranges; when they do so, dominant ones retain their status. As a male climbs a new tree, he rubs his chest against it and sometimes dribbles urine. This scent-marking behaviour probably serves as communication, and individuals are known to sniff the bottom of a newly found tree. Chest gland secretions are complex chemical mixtures — about 40 compounds were identified in one analysis — that vary in composition and concentration with the season and the age of the individual.
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 of the year, particularly during the breeding season, when it serves to attract females and possibly intimidate other males. They also bellow to advertise their presence to their neighbours when they climb a different tree. These sounds signal the male's actual body size, as well as exaggerate it; females pay more attention to bellows that originate from 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. 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. 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 that are trying to pass each other in the tree. This occasionally involves biting. Strangers may wrestle, chase, and bite each other. 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. Pregnant and lactating females are particularly aggressive and attack individuals that come too close. In general, however, koalas tend to avoid fighting due to energy costs.
Koalas are seasonal breeders, and give birth from October to May. Females in oestrus lean their heads back and shake their bodies. Despite these obvious signals, males will try to copulate with any female during this period, mounting them from behind. Because of his much larger size, a male can overpower a female. A female may scream and vigorously fight off her suitors but will accede to one that is dominant or familiar. The commotion can attract other males to the scene, obliging the incumbent to delay mating and fight off the intruders. A female may learn who is more dominant during these fights. Older males usually have accumulated scratches, scars, and cuts on the exposed parts of their noses and their eyelids.
Koalas are induced ovulators. The gestation period lasts 33–35 days, and a female gives birth to one joey (although twins do occur). As marsupials, the young are born tiny and barely formed, weighing no more than 0.5 g (0.02 oz). 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 the rest of its development. Female koalas do not clean their pouches, 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 in the pouch. 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.
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. 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 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. 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.
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 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 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. Koalas usually survive falls from trees and can climb back up, but they can get hurt and even die, particularly 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 and some birds of prey may take them. Koalas are generally not subject to external parasites, other than ticks around the coast. The miteSarcoptes scabiei gives koalas mange, while the bacterium Mycobacterium ulceransskin ulcers, but even these are uncommon. Internal parasites are few and have little effect. These include the tapewormBertiella obesa, commonly found in the intestine, and the nematodesMarsupostrongylus longilarvatus and Durikainema phascolarcti, which are infrequently found in the lungs. In a three-year study of almost 600 koalas taken to the Australia Zoo Wildlife Hospital in Queensland, 73.8% of the animals were infected with parasitic protozoal genus Trypanosoma, the most frequent 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 common 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 north to south, where populations go from being completely infected to being partially uninfected.
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 intense heat and flames. Bushfires also break up the animal's habitat, which isolates them, decreases their numbers and creates genetic bottlenecks. 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.
Foraging and activities 3
Koalas are herbivorous, and while most of their diet consists of eucalypt leaves, they can be found in trees of other genera, such as Acacia, Allocasuarina, Callitris, Leptospermum, and Melaleuca. Though the foliage of over 600 species of Eucalyptus is available, the koala shows a strong preference for around 30. They prefer plant matter with higher protein over fibre and lignin. The most favoured 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 picky eater, the koala is more generalist than some other marsupial species, such as the greater glider. The koala does not need to drink often as it can get enough water in the eucalypt leaves, though larger males may additionally drink water found on the ground or in tree hollows. When feeding, a koala reaches out to grab leaves with one forepaw while the other paws hang on to the branch. Depending on the size of the individual, a koala can walk to the end of a branch or must stay near the base. Each day, koalas eat up to 400 grams (14 oz) of leaves, spread over four to six feeding periods. Despite their adaptations to a low-energy lifestyle, they have meagre fat reserves and need to feed often.
Due to their low-energy diet, koalas limit their activity and 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 very 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. 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, leaping along. The koala usually grooms itself with its hind paws, with their double claws, but sometimes uses its forepaws or mouth.
Etymology 3
The word "koala" comes from the Dharuggula, meaning 'no water'. Although the vowel "u" was originally written in the English orthography as "oo" (in spellings such as coola or koolah — two syllables), the spelling later became "oa" and the word is now pronounced in three syllables, possibly in error.
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", later "koala bear", for its supposed resemblance to a bear. It is also one of several Aboriginal words that made it into International English alongside words like "didgeridoo" and "kangaroo". 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'.
Evolution 3
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. The Vombatiformes are a sister group to a clade that includes macropods (kangaroos and wallabies) and possums. The koala's lineage possibly branched off around 40 million years ago during the Eocene.
The modern koala is the only extant member of Phascolarctidae, a family that includes several extinct genera and species. During the Oligocene and Miocene, koalas lived in rainforests and had more generalised diets. Some species, such as the Riversleigh rainforest koala (Nimiokoala greystanesi) and some species of Perikoala, were around the same size as the modern koala, while others, such as species of Litokoala, were one-half to two-thirds its size. Like the modern species, prehistoric koalas had well developed ear structures which suggests that they also made long-distance vocalisations and had a relatively inactive lifestyle. During the Miocene, the Australian continent began drying out, leading to the decline of rainforests and the spread of open Eucalyptus woodlands. The genus Phascolarctos split from Litokoala in the late Miocene, and had several adaptations that allowed it to live on a specialised eucalyptus diet: a shifting of the palate towards the front of the skull; upper teeth lined by thicker bone, molars located relatively low compared the jaw joint and with more chewing surface; smaller pterygoid fossa; and a larger gap separating the incisor teeth and the molars.
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. The fossil record of the modern koala extends back at least to the middle Pleistocene.
Vombatidae (wombats)
Phascolarctidae (koalas)
AcrobatidaeTarsipedidae (honey possum)
Petauridae (wrist-winged gliders and allies)
Pseudocheiridae (ringtail possums and allies)
Macropodidae (kangaroos, wallabies and allies)
Phalangeridae (brushtail possums and cuscuses)
Burramyidae (pygmy possums)
Thylacoleonidae (extinct marsupial lion and allies)
Vombatomorphia (wombats and fossil relatives)
Priscakoala lucyturnbullaeMadakoala spp.
Perikoala robustusNimiokoala greystanesiLitokoala dicksmithiLitokoala kutjamarpensisPhascolarctos cinereus
Sources and Credits
- (c) Michael Jefferies, some rights reserved (CC BY-NC), http://www.flickr.com/photos/14573979@N00/2202492709
- (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Phascolarctos_cinereus
- (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Koala
