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For other uses, see Koala (disambiguation).

The koala (Phascolarctos cinereus, or, inaccurately, koala bear[a]) is an arborealherbivorousmarsupial 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, 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 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.

Koalas typically inhabit open eucalypt 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 bushfires 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Botanist Robert Brown wrote the first detailed scientific description of the koala in 1814, although his work remained unpublished for 180 years.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 recognised worldwide as a symbol of Australia. Koalas are listed as Vulnerable by the International Union for Conservation of Nature.[1] The Australian government similarly lists specific populations in Queensland and New South Wales as Vulnerable.[4] 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 urbanisation.

Etymology

The word koala comes from the Dharuggula. 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.[5] Because of the koala's supposed resemblance to a bear, it was often miscalled the koala bear, particularly by early settlers.[6] The generic name, Phascolarctos, is derived from the Greek words phaskolos "pouch" and arktos "bear". The specific name, cinereus, is Latin for "ash coloured".[7]

Taxonomy and evolution

The koala was given its generic name Phascolarctos in 1816 by French zoologist Henri Marie Ducrotay de Blainville,[9] who would not give it a specific name until further review. In 1819, German zoologist Georg August Goldfuss gave it the binomialLipurus cinereus. Because Phascolarctos was published first, according to the International Code of Zoological Nomenclature, it has priority as the official name of the genus.[10] French naturalist Anselme Gaëtan Desmarest proposed the name Phascolartos fuscus in 1820, suggesting that the brown-coloured versions were a different species than the grey ones. Other names suggested by European authors included Marodactylus cinereus by Goldfuss in 1820, P. flindersii by René Primevère Lesson in 1827, and P. koala by John Edward Gray in 1827.[2]

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.[11] The Vombatiformes are a sister group to a clade that includes macropods (kangaroos and wallabies) and possums.[12] The ancestors of vombatiforms were likely arboreal,[8] and the koala's lineage was possibly the first to branch off around 40 million years ago during the Eocene.[13]

The modern koala is the only extant member of Phascolarctidae, a family that once included several genera and species. During the Oligocene and Miocene, koalas lived in rainforests and had less specialised diets.[14] 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.[15] Like the modern species, prehistoric koalas had well developed ear structures which suggests that long-distance vocalising and sedentism developed early.[14] 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[14][16] 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; larger molars and premolars; smaller pterygoid fossa;[14] and a larger gap between the molar and the incisor teeth.[17]

During the Pliocene and Pleistocene, when Australia experienced changes in climate and vegetation, koala species grew larger.[15]P. cinereus may have emerged as a dwarf form of the giant koala (P. stirtoni). The reduction in the size of large mammals has been seen as a common phenomenon worldwide during the late Pleistocene, and several Australian mammals, such as the agile wallaby, are traditionally believed to have resulted from this dwarfing. A 2008 study questions this hypothesis, noting that P. cinereus and P. stirtoni were sympatric during the middle to late Pleistocene, and possibly as early as the Pliocene.[18] The fossil record of the modern koala extends back at least to the middle Pleistocene.[19]

Genetics and variations

Traditionally, three distinct subspecies have been recognised: 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 colour 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.[20][21] 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.[21] Other studies have found that koala populations have high levels of inbreeding and low genetic variation.[22][23] Such low genetic diversity may have been a characteristic of koala populations since the late Pleistocene.[24] Rivers and roads have been shown to limit gene flow and contribute to the genetic differentiation of southeast Queensland populations.[25] In April 2013, scientists from the Australian Museum and Queensland University of Technology announced they had fully sequenced the koala genome.[26]

Description

The koala is a stocky animal with a large head and vestigial or non-existent tail.[27][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.[20] 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 hairless patches.[30] As in most marsupials, the male koala has a bifurcated penis,[31] and the female has two lateral vaginas and two separate uteri.[27] The male's penile sheath contains naturally occurring bacteria that play an important role in fertilisation.[32] The female's pouch opening is tightened by a sphincter that keeps the young from falling out.[33]

The pelage of the koala is thicker and longer on the back, and shorter on the belly. The ears have thick fur on both the inside and outside.[29] The back fur colour varies from light grey to chocolate brown.[27] The belly fur is whitish; on the rump it is dappled whitish, and darker at the back.[28] 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.[34] 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 grasp small branches. On the hindpaws, the second and third digits are fused, a typical condition for members of the Diprotodontia, and the attached claws (which are still separate) are used for grooming.[35] As in humans and other primates, koalas have friction ridges on their paws.[36] The animal has a sturdy skeleton and a short, muscular upper body with proportionately long upper limbs that contribute to its climbing and grasping abilities. Additional climbing strength is achieved with thigh muscles that attach to the shinbone lower than other animals.[37] The koala has a cartilaginous pad at the end of the spine that may make it more comfortable when it perches in the fork of a tree.[33]

The koala has one of the smallest brains in proportion to body weight of any mammal,[38] being 60% smaller than that of a typical diprotodont, weighing only 19.2 g (0.68 oz).[39] The brain's surface is fairly smooth, typical for a "primitive" animal.[40] It occupies only 61% of the cranial cavity[38] and is pressed against the inside surface by cerebrospinal fluid. The function of this relatively large amount of fluid is not known, although one possibility is that it acts as a shock absorber, cushioning the brain if the animal falls from a tree.[40] 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.[38] Because of its small brain, the koala has a limited ability to perform complex, unfamiliar behaviours. For example, when presented with plucked leaves on a flat surface, the animal cannot adapt to the change in its normal feeding routine and will not eat the leaves.[41] The koala's olfactory senses are normal, and it is known to sniff the oils of individual branchlets to assess their edibility.[38] Its nose is fairly large and covered in leathery skin. Its round ears provide it with good hearing,[33] and it has a well-developed middle ear.[14] A koala's vision is not well developed,[33] and its relatively small eyes are unusual among marsupials in that the pupils have vertical slits.[29] Koalas make use of a novel vocal organ to produce low-pitched sounds (see social spacing, below). Unlike typical mammalian vocal cords, which are folds in the larynx, these organs are placed in the velum (soft palate) and are called velar vocal cords.[42]

The koala has several adaptations for its eucalypt diet, which is of low nutritive value, of high toxicity, and high in dietary fibre.[43] 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 incisors are used for grasping leaves, which are then passed to the premolars to be snipped at the petiole before being passed to the highly cusped molars, where they are shredded into small pieces.[44] Koalas may also store food in their cheek pouches before it is ready to be chewed.[45] The partially worn molars of middle-aged koalas are optimal for breaking the leaves into small particles, resulting in more efficient stomach digestion and nutrient absorption in the small intestine,[46] which digests the eucalyptus leaves to provide most of the animal's energy.[44] A koala sometimes regurgitates the food into the mouth to be chewed a second time.[47]

Unlike kangaroos and eucalyptus-eating possums, 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.[44] This is made possible by the extraordinary length of their caecum—200 cm (80 in) long and 10 cm (4 in) in diameter—the largest proportionally of any animal.[48] Koalas can select which food particles to retain for longer fermentation and which to pass through. Large particles typically pass through more quickly, as they would take more time to digest.[44] While the hindgut is proportionally larger in the koala than in other herbivores, only 10% of the animal's energy is obtained from fermentation. Since the koala gains a low amount of energy from its diet, its metabolic rate is half that of a typical mammal,[43] although this can vary between seasons and sexes.[44] The koala conserves water by passing relatively dry faecal pellets high in undigested fibre, and by storing water in the caecum.[46]

Ecology and behaviour

The koala's geographic range covers roughly 1,000,000 km2 (390,000 sq mi), and 30 ecoregions.[49] 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.[1] The population on Magnetic Island represents the northern limit of its range.[49] 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.[50]

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.[1] Koalas can be found in habitats ranging from relatively open forests to woodlands, and in climates ranging from tropical to cool temperate.[29] In semi-arid climates, they prefer riparian habitats, where nearby streams and creeks provide refuge during times of drought and extreme heat.[51]

Foraging and activities

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.[52] Although the foliage of over 600 species of Eucalyptus is available, the koala shows a strong preference for around 30.[53] They tend to choose species that have a high protein content and low proportions of fibre and lignin.[46] The most favoured species are Eucalyptus microcorys, E. tereticornis, and E. camaldulensis, which, on average, make up more than 20% of their diet.[54] 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 does not need to drink often;[52] 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.[46] 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.[55] Koalas consume up to 400 grams (14 oz) of leaves a day, spread over four to six feeding sessions.[56] Despite their adaptations to a low-energy lifestyle, they have meagre fat reserves and need to feed often.[57]

Because they get so little energy from their diet, koalas must limit their energy use and sleep 20 hours a day;[58] only 4 hours a day are spent in active movement.[59] 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.[60] 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.[61][62] On warm days, a koala may rest with its back against a branch or lie on its stomach or back with its limbs dangling.[58] During cold, wet periods, it curls itself into a tight ball to conserve energy.[60] 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.[58] The koala usually grooms itself with its hindpaws, but sometimes uses its forepaws or mouth.[63]

Social spacing

Koalas are asocial animals and spend just 15 minutes a day on social behaviours. In Victoria, home ranges are small and have extensive overlap, while in central Queensland they are larger and overlap less.[64] 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 dominate others with their larger body size.[65]Alpha males tend to establish their territories close to breeding females, while younger males are subordinate until they mature and reach full size.[66] Adult males occasionally venture outside their home ranges; when they do so, dominant ones retain their status.[64] When a male enters a new tree, he marks it by rubbing his chest gland against the trunk or a branch; males have occasionally been observed to dribble urine on the trunk. This scent-marking behaviour probably serves as communication, and individuals are known to sniff the base of a tree before climbing.[67] Scent marking is common during aggressive encounters.[68] 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.[69]

Adult males communicate with loud bellows—low pitched sounds that consist of snore-like inhalations and resonant exhalations that sound like growls.[70] These sounds are thought to be generated by unique vocal organs found in koalas.[42] Because of their low frequency, these bellows can travel far through air and vegetation.[71] 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.[72] They also bellow to advertise their presence to their neighbours when they enter a new tree.[71] These sounds signal the male's actual body size, as well as exaggerate it;[73] females pay more attention to bellows that originate from larger males.[74] 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.[70] Young koalas squeak when in distress. As they get older, the squeak develops into a "squawk" produced both when in distress and to show aggression. When another individual climbs over it, a koala makes a low grunt with its mouth closed. Koalas make numerous facial expressions. When snarling, wailing, or squawking, the animal curls the upper lip and points its ears forward. During screams, the lips retract and the ears are drawn back. Females bring their lips forward and raise their ears when agitated.[75]

Agonistic behaviour typically consists of squabbles between individuals climbing over or passing each other. This occasionally involves biting. Males that are strangers may wrestle, chase, and bite each other.[76] In extreme situations, a male may try to displace a smaller rival from a tree. This involves the larger aggressor climbing up and attempting to corner the victim, which tries either to rush past him and climb down or to move to the end of a branch. The aggressor attacks by grasping the target by the shoulders and repeatedly biting him. Once the weaker individual is driven away, the victor bellows and marks the tree.[77] Pregnant and lactating females are particularly aggressive and attack individuals that come too close.[76] In general, however, koalas tend to avoid energy-wasting aggressive behaviour.[66]

Reproduction and development

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 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.[78] Older males usually have accumulated scratches, scars, and cuts on the exposed parts of their noses and on their eyelids.[79]

The koala's gestation period lasts 33–35 days,[80] 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.[81] Unlike most other marsupials, the koala does not clean her pouch.[82]

A female koala has two teats; the joey attaches itself to one of them and suckles for the rest of its pouch life.[81] 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.[83] 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.[84]

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.[85] 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 colour. Having permanently left the pouch, it rides on its mother's back for transportation, learning to climb by grasping branches.[86] 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 behaviour towards them.[87]

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,[88] although they can produce sperm as early as two years.[87] 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.[69] 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.[89]

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.[90] 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.[91] 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.[92]

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 miteSarcoptes scabiei, and skin ulcers from the bacterium Mycobacterium ulcerans, but neither is common. Internal parasites are few and largely harmless.[91] These include the tapewormBertiella obesa, commonly found in the intestine, and the nematodesMarsupostrongylus longilarvatus and Durikainema phascolarcti, which are infrequently found in the lungs.[93] 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.[94]

Koalas can be subject to pathogens such as Chlamydiaceae bacteria,[91] which can cause keratoconjunctivitis, urinary tract infection, and reproductive tract infection.[95] Such infections are widespread on the mainland, but absent in some island populations.[96] 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.[97]

The animals are vulnerable to bushfires due to their slow movements and the flammability of eucalypt trees.[98] The koala instinctively seeks refuge in the higher branches, where it is vulnerable to intense heat and flames. Bushfires also fragment the animal's habitat, which restricts their movement and leads to population decline and loss of genetic diversity.[99]Dehydration and overheating can also prove fatal.[100] 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.[101]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.[41] 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.[102] 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.[103]

Human relations

History

Reconstructions of the ancient koalas Nimiokoala (larger), and Litokoala (smaller), from the Miocene Riversleigh Fauna
A young joey, preserved at Port Macquarie Koala Hospital

This article is about the living animal. For the kangaroo as a food, see Kangaroo meat. For other meanings, see Kangaroo (disambiguation).

The kangaroo is a marsupial from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, especially those of the genus Macropus: the red kangaroo, antilopine kangaroo, eastern grey kangaroo, and western grey kangaroo.[1] Kangaroos are indigenous to Australia. The Australian government estimates that 34.3 million kangaroos lived within the commercial harvest areas of Australia in 2011, up from 25.1 million one year earlier.[2]

As with the terms "wallaroo" and "wallaby", "kangaroo" refers to a polyphyletic grouping of species. All three refer to members of the same taxonomic family, Macropodidae, and are distinguished according to size. The largest species in the family are called "kangaroos" and the smallest are generally called "wallabies". The term "wallaroos" refers to species of an intermediate size.[3] There is also the tree-kangaroo, another genus of macropod, which inhabits the tropical rainforests of New Guinea, far northeastern Queensland and some of the islands in the region. A general idea of the relative size of these informal terms could be:

  • wallabies: head and body length of 45–105 cm and tail length of 33–75 cm; The dwarf wallaby (the smallest member) length is 46 cm and weigh of 1.6 kg;
  • tree-kangaroos: from Lumholtz's tree-kangaroo body and head length of 48–65 cm, tail of 60–74 cm, weigh of 7.2 kg (16 lb) for males and 5.9 kg (13 lb) for females; to the grizzled tree-kangaroo length of 75–90 cm (30 to 35 in) and weight of 8–15 kg (18–33 lb);
  • wallaroos: the black wallaroo, the smallest by far, with a tail length of 60–70 cm and weight of 19–22 kg for males and 13 kg for females;
  • kangaroos: a large male can be 2 m (6 ft 7 in) tall and weigh 90 kg (200 lb).

Kangaroos have large, powerful hind legs, large feet adapted for leaping, a long muscular tail for balance, and a small head. Like most marsupials, female kangaroos have a pouch called a marsupium in which joeys complete postnatal development.

The large kangaroos have adapted much better than the smaller macropods to land clearing for pastoral agriculture and habitat changes brought to the Australian landscape by humans. Many of the smaller species are rare and endangered, while kangaroos are relatively plentiful.

The kangaroo is a symbol of Australia and appears on the Australian coat of arms[4] and on some of its currency[5] and is used by some of Australia's well known organisations, including Qantas[6] and the Royal Australian Air Force.[7] The kangaroo is important to both Australian culture and the national image, and consequently there are numerous popular culture references.

Wild kangaroos are shot for meat, leather hides, and to protect grazing land.[8] Although controversial, kangaroo meat has perceived health benefits for human consumption compared with traditional meats due to the low level of fat on kangaroos.[9]

Terminology

The word "kangaroo" derives from the Guugu Yimithirr word gangurru, referring to grey kangaroos.[10][11] The name was first recorded as "kanguru" on 12 July 1770 in an entry in the diary of Sir Joseph Banks; this occurred at the site of modern Cooktown, on the banks of the Endeavour River, where HMS Endeavour under the command of Lieutenant James Cook was beached for almost seven weeks to repair damage sustained on the Great Barrier Reef.[12] Cook first referred to kangaroos in his diary entry of 4 August. Guugu Yimithirr is the language of the people of the area.

A common myth about the kangaroo's English name is that "kangaroo" was a Guugu Yimithirr phrase for "I don't understand you."[13] According to this legend, Cook and Banks were exploring the area when they happened upon the animal. They asked a nearby local what the creatures were called. The local responded "Kangaroo", meaning "I don't understand you", which Cook took to be the name of the creature. This myth was debunked in the 1970s by linguist John B. Haviland in his research with the Guugu Yimithirr people.[14]

Kangaroos are often colloquially referred to as "roos".[15] Male kangaroos are called bucks, boomers, jacks, or old men; females are does, flyers, or jills, and the young ones are joeys.[16] The collective noun for kangaroos is a mob, troop, or court.[17]

Taxonomy and description

There are four species that are commonly referred to as kangaroos:

  • The red kangaroo (Macropus rufus) is the largest surviving marsupial anywhere in the world. It occupies the arid and semi-arid centre of the country. The highest population densities of the red kangaroo occur in the rangelands of western New South Wales. Red kangaroos are commonly mistaken as the most abundant species of kangaroo, but eastern greys actually have a larger population.[18] A large male can be 2 metres (6 ft 7 in) tall and weigh 90 kg (200 lb).[19]
  • The eastern grey kangaroo (Macropus giganteus) is less well-known than the red (outside Australia), but the most often seen, as its range covers the fertile eastern part of the country. The range of the eastern grey kangaroo extends from the top of the Cape York Peninsula in north Queensland down to Victoria, as well as areas of south-eastern Australia and Tasmania. Population densities of eastern grey kangaroos usually peak near 100 per km2 in suitable habitats of open woodlands. Populations are more limited in areas of land clearance, such as farmland, where forest and woodland habitats are limited in size or abundance.[18]
  • The western grey kangaroo (Macropus fuliginosus) is slightly smaller again at about 54 kg (119 lb) for a large male. It is found in the southern part of Western Australia, South Australia near the coast, and the Darling River basin. The highest population densities occur in the western Riverina district of New South Wales and in western areas of the Nullarbor Plain in Western Australia. Populations may have declined, particularly in agricultural areas. The species has a high tolerance to the plant toxin sodium fluoroacetate, which indicates a possible origin from the south-west region of Australia.[18]
  • The antilopine kangaroo (Macropus antilopinus) is, essentially, the far-northern equivalent of the eastern and western grey kangaroos. It is sometimes referred to as the antilopine wallaroo, but in behaviour and habitat it is more similar to red and grey kangaroos. Like them, it is a creature of the grassy plains and woodlands, and gregarious. Its name comes from its fur, which is similar in colour and texture to that of antelopes. Characteristically, the noses of males swell behind the nostrils. This enlarges nasal passages and allows them to release more heat in hot and humid climates.[18]

In addition, there are about 50 smaller macropods closely related to the kangaroo in the family Macropodidae. Kangaroos and other macropods share a common ancestor with Phalangeridae from the mid-Miocene.[20] This ancestor was likely arboreal and lived in the canopies of the extensive forests that covered most of Australia at that time, when the climate was much wetter, and fed on leaves and stems.[21] From the late Miocene though the Pliocene and into the Pleistocene the climate got drier which led to a decline of forests and expansion of grasslands. At this time there was a radiation of macropodids characterised by enlarged body size and adaptation to the low quality grass diet with the development of foregut fermentation.[21] The most numerous early macropods, the Balbaridae and Bulungmayinae, became extinct in the late Miocene around 5–10 mya.[22] There is dispute over the relationships of the two groups to modern kangaroos and rat kangaroos. Some argue that the balbarines were the ancestors of rat kangaroos and the bulungmayines were the ancestors of kangaroos.[23] while others hold the contrary view.[24]

The middle to late bulungmayines, Gungaroo and Wanburoo lacked digit 1 of the hind foot and digits 2 and 3 were reduced and partly under the large digit 4, much like the modern kangaroo foot. This would indicate that they were bipedal. In addition their ankle bones had an articulation that would have prohibited much lateral movements, an adaptation for bipedal hopping.[22] Species related to the modern grey kangaroos and wallaroos begin to appear in the Pliocene. The red kangaroo appears to be the most recently evolved kangaroo with its fossil record not going back beyond the Pleistocene period, 1–2 mya.[25]

Europeans have long regarded kangaroos as strange animals. Early explorers described them as creatures that had heads like deer (without antlers), stood upright like men, and hopped like frogs. Combined with the two-headed appearance of a mother kangaroo, this led many back home to dismiss them as travellers' tales for quite some time.[citation needed] The first kangaroo to be exhibited in the western world was an example shot by John Gore, an officer on Captain Cook's Endeavour in 1770.[26][27] The animal was shot and its skin and skull transported back to England whereupon it was stuffed (by taxidermists who had never seen the animal before) and displayed to the general public as a curiosity. The first glimpse of a kangaroo for many 18th-century Britons was a painting by George Stubbs.[28]

Comparison with wallabies

Kangaroos and wallabies belong to the same taxonomic family (Macropodidae) and often the same genera, but kangaroos are specifically categorised into the six largest species of the family. The term wallaby is an informal designation generally used for any macropod that is smaller than a kangaroo or wallaroo that has not been designated otherwise.[3]

Biology and behaviour

See also: Red kangaroo § Behaviour, and Eastern grey kangaroo § Behaviour

Locomotion

Kangaroos are the only large animals to use hopping as a means of locomotion. The comfortable hopping speed for a red kangaroo is about 20–25 km/h (12–16 mph), but speeds of up to 70 km/h (43 mph) can be attained over short distances, while it can sustain a speed of 40 km/h (25 mph) for nearly 2 km (1.2 mi).[29] This fast and energy-efficient method of travel has evolved because of the need to regularly cover large distances in search of food and water, rather than the need to escape predators.[citation needed] At slow speeds, it employs pentapedal locomotion, using its tail to form a tripod with its two forelimbs while bringing its hind feet forward.[30] Kangaroos are adept swimmers, and often flee into waterways if threatened by a predator. If pursued into the water, a kangaroo may use its forepaws to hold the predator underwater so as to drown it.[31]

Diet

Kangaroos have single-chambered stomachs quite unlike those of cattle and sheep.[32][33] They sometimes regurgitate the vegetation they have eaten, chew it as cud, and then swallow it again for final digestion, but this is a different, and more strenuous, activity than it is in ruminants, and does not take place as frequently.[34] Different species of kangaroos have different diets, although all are strict herbivores. The eastern grey kangaroo is predominantly a grazer, eating a wide variety of grasses, whereas some other species (e.g. the red kangaroo) include significant amounts of shrubs in their diets. The smaller species of kangaroos also consume hypogeal fungi. Many species are nocturnal,[35] and crepuscular,[36][37] usually spending the days resting in shade, and the cool evenings, nights and mornings moving about and feeding.

Because of its grazing, the kangaroo has developed specialised teeth. Its incisors are able to crop grass close to the ground, and its molars chop and grind the grass. Since the two sides of the lower jaw are not joined together, the lower incisors are farther apart, giving the kangaroo a wider bite. The silica in grass is abrasive, so kangaroo molars move forward as they are ground down, and eventually fall out, replaced by new teeth that grow in the back.[38] This process is known as polyphyodonty and amongst other mammals, only occurs in elephants and manatees.

Absence of digestive methane release

Despite having herbivorous diets similar to ruminants such as cattle, which release large quantities of methane through exhaling and eructation (burping), kangaroos release virtually none. The hydrogen byproduct of fermentation is instead converted into acetate, which is then used to provide further energy. Scientists are interested in the possibility of transferring the bacteria responsible from kangaroos to cattle, since the greenhouse gas effect of methane is 23 times greater than that of carbon dioxide, per molecule.[39]

Social and sexual behaviour

Groups of kangaroos are called mobs, which usually have 10 or more kangaroos in them. Living in mobs can provide protection for some of the weaker members of the group.[17] The size and stability of the mobs vary between geographic regions,[21] with eastern Australia having larger and more stable aggregations than in arid areas farther west.[21] Larger aggregations display high amounts of interactions and complex social structures, comparable to that of ungulates.[21] One common behaviour is nose touching and sniffing, which mostly occurs when an individual joins a group.[25] The kangaroo performing the sniffing gains much information from smell cues. This behaviour enforces social cohesion without consequent aggression. During mutual sniffing, if one kangaroo is smaller, it will hold its body closer to the ground and its head will quiver, which serves as a possible form of submission.[25] Greetings between males and females are common, with larger males being the most involved in meeting females. Most other non-antagonistic behaviour occurs between mothers and their young. Mother and young reinforce their bond though grooming. A mother will groom her young during or after it is suckling.[25] A joey will nuzzle its mother’s pouch if it wants access to it.

Sexual activity of kangaroos consists of consort pairs.[40]Oestrous females roam widely and attract the attention of males with conspicuous signals.[40] A male will monitor a female and follow her every movement. He sniffs her urine to see if she is in oestrus, a process exhibiting the flehmen response. The male will then proceed to approach her slowly to avoid alarming her.[21] If the female does not run away, the male will continue by licking, pawing, and scratching her, and copulation will follow.[21] After copulation is over, the male will move on to another female. Consort pairing may take several days and the copulation is also long. Thus, a consort pair is likely to attract the attention of a rival male.[40] As larger males are tending bonds with females near oestrus, smaller males will tend to females that are farther from oestrus.[21] Dominant males can avoid having to sort through females to determine their reproductive status by searching for tending bonds held by the largest male they can displace without a fight.[21]

Fighting has been described in all species of kangaroos. Fights between kangaroos can be brief or long and ritualised.[25] In highly competitive situations, such as males fighting for access to oestrous females or at limited drinking spots, the fights are brief.[25] Both sexes will fight for drinking spots, but long, ritualised fighting or "boxing" is largely done by males. Smaller males fight more often near females in oestrus, while the large males in consorts do not seem to get involved. Ritualised fights can arise suddenly when males are grazing together. However, most fights are preceded by two males scratching and grooming each other.[25] One or both of them will adopt a high standing posture, with one male issuing a challenge by grasping the other male’s neck with its forepaw. Sometimes, the challenge will be declined. Large males often reject challenges by smaller males. During fighting, the combatants adopt a high standing posture and paw at each other's heads, shoulders and chests. They will also lock forearms and wrestle and push each other as well as balance on their tails to kick each other in the abdomens.[25]

Brief fights are similar except there is no forearm locking. The losing combatant seems to use kicking more often, perhaps to parry the thrusts of the eventual winner. A winner is decided when a kangaroo breaks off the fight and retreats. Winners are able to push their opponents backwards or down to the ground. They also seem to grasp their opponents when they break contact and push them away.[25] The initiators of the fights are usually the winners. These fights may serve to establish dominance hierarchies among males, as winners of fights have been seen to displace their opponent from resting sites later in the day.[25] Dominant males may also pull grass to intimidate subordinates.[21]

Predators

Kangaroos have few natural predators. The thylacine, considered by palaeontologists to have once been a major natural predator of the kangaroo, is now extinct. Other extinct predators included the marsupial lion, Megalania and the Wonambi. However, with the arrival of humans in Australia at least 50,000 years ago and the introduction of the dingo about 5,000 years ago, kangaroos have had to adapt. Wedge-tailed eagles and other raptors usually eat kangaroo carrion. Goannas and other carnivorous reptiles also pose a danger to smaller kangaroo species when other food sources are lacking.

Along with dingos, introduced species such as foxes, feral cats, and both domestic and feral dogs, pose a threat to kangaroo populations. Kangaroos and wallabies are adept swimmers, and often flee into waterways if presented with the option. If pursued into the water, a large kangaroo may use its forepaws to hold the predator underwater so as to drown it.[31] Another defensive tactic described by witnesses is catching the attacking dog with the forepaws and disembowelling it with the hind legs.

Adaptations

Kangaroos have developed a number of adaptations to a dry, infertile country and highly variable climate. As with all marsupials, the young are born at a very early stage of development—after a gestation of 31–36 days. At this stage, only the forelimbs are somewhat developed, to allow the newborn to climb to the pouch and attach to a teat. In comparison, a human embryo at a similar stage of development would be about seven weeks old, and premature babies born at less than 23 weeks are usually not mature enough to survive. When the joey is born, it is about the size of a lima bean. The joey will usually stay in the pouch for about nine months (180–320 days for the Western Grey) before starting to leave the pouch for small periods of time. It is usually fed by its mother until reaching 18 months.

The female kangaroo is usually pregnant in permanence, except on the day she gives birth; however, she has the ability to freeze the development of an embryo until the previous joey is able to leave the pouch. This is known as diapause, and will occur in times of drought and in areas with poor food sources. The composition of the milk produced by the mother varies according to the needs of the joey. In addition, the mother is able to produce two different kinds of milk simultaneously for the newborn and the older joey still in the pouch.

Unusually, during a dry period, males will not produce sperm, and females will only conceive if enough rain has fallen to produce a large quantity of green vegetation.[41]

Kangaroos and wallabies have large, elastic tendons in their hind legs. They store elastic strain energy in the tendons of their large hind legs, providing most of the energy required for each hop by the spring action of the tendons rather than by any muscular effort.[42] This is true in all animal species which have muscles connected to their skeletons through elastic elements such as tendons, but the effect is more pronounced in kangaroos.

There is also a link between the hopping action and breathing: as the feet leave the ground, air is expelled from the lungs; bringing the feet forward ready for landing refills the lungs, providing further energy efficiency. Studies of kangaroos and wallabies have demonstrated, beyond the minimum energy expenditure required to hop at all, increased speed requires very little extra effort (much less than the same speed increase in, say, a horse, dog or human), and the extra energy is required to carry extra weight. For kangaroos, the key benefit of hopping is not speed to escape predators—the top speed of a kangaroo is no higher than that of a similarly sized quadruped, and the Australian native predators are in any case less fearsome than those of other countries—but economy: in an infertile country with highly variable weather patterns, the ability of a kangaroo to travel long distances at moderately high speed in search of food sources is crucial to survival.

New research has revealed that a kangaroos tail acts as a third leg rather than just a balancing strut. Kangaroos have a unique three-stage walk where they plant their front legs and tail first, then push off their tail, followed lastly by the back legs. The propulsive force of the tail is equal to that of both the front and hind legs combined and performs as much work as what a human leg walking can at the same speed. [43]

A DNA sequencing project of the genome of a member of the kangaroo family, the tammar wallaby, was started in 2004. It was a collaboration between Australia (mainly funded by the state of Victoria) and the National Institutes of Health in the US.[44] The tammar's genome was fully sequenced in 2011.[45] The genome of a marsupial such as the kangaroo is of great interest to scientists studying comparative genomics, because marsupials are at an ideal degree of evolutionary divergence from humans: mice are too close and have not developed many different functions, while birds are genetically too remote. The dairy industry could also benefit from this project.[46]

Blindness

Eye disease is rare but not new among kangaroos. The first official report of kangaroo blindness took place in 1994, in central New South Wales. The following year, reports of blind kangaroos appeared in Victoria and South Australia. By 1996, the disease had spread "across the desert to Western Australia".[citation needed] Australian authorities were concerned the disease could spread to other livestock and possibly humans. Researchers at the Australian Animal Health Laboratories in Geelong detected a virus called the Wallal virus in two species of midges, believed to have been the carriers.[47][48]Veterinarians also discovered fewer than 3% of kangaroos exposed to the virus developed blindness.[49]

Reproduction and life cycle

See also: Red kangaroo § Reproduction, and Eastern grey kangaroo § Reproduction

Kangaroo reproduction is similar to that of opossums. The egg (still contained in the shell membrane, a few micrometres thick, and with only a small quantity of yolk within it) descends from the ovary into the uterus. There it is fertilised and quickly develops into a neonate. Even in the largest kangaroo (the red kangaroo) the neonate emerges after only 33 days. Usually, only one young is born at a time. It is blind, hairless, and only a few centimetres long; its hindlegs are mere stumps; it instead uses its more developed forelegs to climb its way through the thick fur on its mother's abdomen into the pouch, which takes about three to five minutes. Once in the pouch, it fastens onto one of the four teats and starts to feed. Almost immediately, the mother's sexual cycle starts again. Another egg descends into the uterus and she becomes sexually receptive. Then, if she mates and a second egg is fertilised, its development is temporarily halted. Meanwhile, the neonate in the pouch grows rapidly. After about 190 days, the baby (joey) is sufficiently large and developed to make its full emergence out of the pouch, after sticking its head out for a few weeks until it eventually feels safe enough to fully emerge. From then on, it spends increasing time in the outside world and eventually, after about 235 days, it leaves the pouch for the last time.[50] The lifespan of kangaroos averages at six years in the wild[51] to in excess of 20 years in captivity, varying by species.[52] Most individuals, however, do not reach maturity in the wild.[53][54]

Interaction with humans

The kangaroo has always been a very important animal for Australian Aborigines, for its meat, hide, bone, and tendon. Kangaroo hides were also sometimes used for recreation; in particular there are accounts of some tribes (Kurnai) using stuffed kangaroo scrotum as a ball for the traditional football game of marngrook. In addition, there were important Dreaming stories and ceremonies involving the kangaroo. Aherrenge is a current kangaroo dreaming site in the Northern Territory.[55]

Unlike many of the smaller macropods, kangaroos have fared well since European settlement. European settlers cut down forests to create vast grasslands for sheep and cattle grazing, added stock watering points in arid areas, and have substantially reduced the number of dingoes.

Kangaroos are shy and retiring by nature, and in normal circumstances present no threat to humans. In 2003, Lulu, an eastern grey which had been hand-reared, saved a farmer's life by alerting family members to his location when he was injured by a falling tree branch. She received the RSPCA Australia National Animal Valour Award on 19 May 2004.[56][57][58]

There are very few records of kangaroos attacking humans without provocation; however, several such unprovoked attacks in 2004 spurred fears of a rabies-like disease possibly affecting the marsupials. The only reliably documented case of a fatality from a kangaroo attack occurred in New South Wales, in 1936. A hunter was killed when he tried to rescue his two dogs from a heated fray. Other suggested causes for erratic and dangerous kangaroo behaviour include extreme thirst and hunger. In July 2011, a male red kangaroo attacked a 94-year-old woman in her own backyard as well as her son and two police officers responding to the situation. The kangaroo was capsicum sprayed (pepper sprayed) and later put down after the attack.[59][60]

Conflict with vehicles

A collision with a vehicle is capable of killing a kangaroo. Kangaroos dazzled by headlights or startled by engine noise often leap in front of cars. Since kangaroos in mid-bound can reach speeds of around 50 km/h (31 mph) and are relatively heavy, the force of impact can be severe. Small vehicles may be destroyed, while larger vehicles may suffer engine damage. The risk of harm or death to vehicle occupants is greatly increased if the windscreen is the point of impact. As a result, "kangaroo crossing" signs are commonplace in Australia.

Vehicles that frequent isolated roads, where roadside assistance may be scarce, are often fitted with "roo bars" to minimise damage caused by collision. Bonnet-mounted devices, designed to scare wildlife off the road with ultrasound and other methods, have been devised and marketed.

If a female is the victim of a collision, animal welfare groups ask that her pouch be checked for any surviving joey, in which case it may be removed to a wildlife sanctuary or veterinary surgeon for rehabilitation. Likewise, when an adult kangaroo is injured in a collision, a vet, the RSPCA Australia or the National Parks and Wildlife Service can be consulted for instructions on proper care. In New South Wales, rehabilitation of kangaroos is carried out by volunteers from WIRES. Council road signs often list phone numbers for callers to report injured animals.

Emblems and popular culture

Main article: Kangaroo emblems and popular culture

The kangaroo is a recognisable symbol of Australia. The kangaroo and emu feature on the Australian Coat of Arms. Kangaroos have also been featured on coins, most notably the five kangaroos on the Australian one dollar coin. The Australian Made logo consists of a golden kangaroo in a green triangle to show that a product is grown or made in Australia.

The kangaroo and wallaby feature predominantly in Australian sports teams names and mascots. Examples include the Australian national rugby league team (the Kangaroos) and the Australian national rugby union team (the Wallabies). Australia’s national airline, Qantas, uses a bounding kangaroo for its logo.

Kangaroos are well represented in films, television, books, toys and souvenirs around the world. Skippy the Bush Kangaroo was the star of the popular 1960s Australian children’s television series of the same name. Kangaroos are featured in the Rolf Harris song Tie Me Kangaroo Down, Sport and several Christmas carols.

Meat

Main article: Kangaroo meat

Historically, the kangaroo has been a source of food for indigenous Australians. Kangaroo meat is high in protein and low in fat (about 2%). Kangaroo meat has a high concentration of conjugated linoleic acid (CLA) compared with other foods, and is a rich source of vitamins and minerals.[61] Low fat diets rich in CLA have been studied for their potential in reducing obesity and atherosclerosis.[62][63]

Most kangaroo meat is currently sourced from wild animals as a byproduct of population control programs.[citation needed] Kangaroos are hunted by licensed shooters in accordance with a strict code of practice and are protected by state and federal legislation.[citation needed]

Kangaroo meat is exported to many countries around the world.

See also

References

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  12. ^Bruce Moore, The Vocabulary of Australian English, Australian National Dictionary Centre, Australian National University
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  14. ^Haviland, John B. (1974). "A last look at Cook's Guugu-Yimidhirr wordlist"(PDF). Oceania. 44 (3): 216–232. Retrieved 13 April 2008. 
  15. ^"Roo". Compact Oxford English Dictionary. Ask Oxford.com. Archived from the original on 11 February 2007. Retrieved 31 December 2006. 
  16. ^"Kangaroo and Wallaby". San Diego Zoo. Zoological Society of San Diego. Archived from the original on 27 September 2011. Retrieved 2 October 2011. 
  17. ^ abSydenham, S; Thomas, R. "Kangaroos". Kidcyber. Archived from the original on 3 September 2011. Retrieved 2 October 2011. 
  18. ^ abcdDawson, Terence (2012). Kangaroos (2nd ed.). Collingwood, VIC: CSIRO Publishing. 
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  20. ^Rice, W.D.L. (1978). "Historical introduction to studies on the evolution and phylogeny of the Macropodidae". Australian Mammalogy. 2: 1–14. 
  21. ^ abcdefghijMcCullough 2000
  22. ^ abTyndale-Biscoe, H (2005). Life of Marsupials. CSIRO Publishing. p. 302. ISBN 978-0-643-06257-3. 
  23. ^Cooke B, Kear B (1999). "Evolution and diversity of kangaroos (Macropodoidea, Marsupialia)". Australian Mammalogy. 21: 27–29. 
  24. ^Flannery, T.F. (1989). "Phylogeny of the Macropodoidea; a study in convergence". In Grigg G.; Jarman P.; Hume I.D. Kangaroos, Wallabies and Rat-kangaroos. Sydney: Surrey Beatty. pp. 1–46. ISBN 0-949324-22-1. 
  25. ^ abcdefghijDawson, Terence J. (1995). Kangaroos: Biology of the Largest Marsupials. Cornell University Press/Comstock Publishing. ISBN 0-8014-8262-3. 
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  27. ^Cowley, Des; Hubber, Brian (2000). Barnes, John; Burt, Sandra, eds. "Kangaroo". The La Trobe Journal (66): 4–5. ISSN 1441-3760
Kangaroos in native grassland
Newborn joey sucking on a teat in the pouch
A "kangaroo crossing" sign on an Australian highway
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