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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. Kangaroos are endemic 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.
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. 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 an unofficial symbol of Australia and appears as an emblem on the Australian coat of arms and on some of its currency and is used by some of Australia's well known organisations, including Qantas and the Royal Australian Air Force. 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. Although controversial, kangaroo meat has perceived health benefits for human consumption compared with traditional meats due to the low level of fat on kangaroos.
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). 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. At slow speeds, it employs pentapedal locomotion, using its tail to form a tripod with its two forelimbs while bringing its hind feet forward. 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.
Kangaroos have chambered stomachs similar to those of cattle and sheep. They regurgitate the vegetation they have eaten, chew it as cud, and then swallow it again for final digestion. 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, and crepuscular, 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. 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
Social and sexual behaviour
Groups of kangaroos are called mobs. Mobs usually have 10 or more kangaroos in them. Living in mobs provides protection for some of the weaker members of the group. The size and stability of the mobs vary between geographic regions, with eastern Australia having larger and more stable aggregations than in arid areas farther west. Larger aggregations display high amounts of interactions and complex social structures, comparable to that of ungulates. One common behaviour is nose touching and sniffing, which mostly occurs when an individual joins a group. The kangaroos performing the sniffing gain 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; this is possibly a form of submission. 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. A joey will nuzzle its mother’s pouch if it wants access to it.
Sexual activity of kangaroos consists of consort pairs.[Oestrous females roam widely and attract the attention of males with conspicuous signals. 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. If the female does not run away, the male will continue by licking, pawing, and scratching her, and copulation will follow. 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. As larger males are tending bonds with females near oestrus, smaller males will tend to females that are farther from oestrus. 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.
Fighting has been described in all species of kangaroos. Fights between kangaroos can be brief or long and ritualised. In highly competitive situations, such as males fighting for access to oestrous females or at limited drinking spots, the fights are brief. 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. 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.
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. Winners are 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. 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. Dominant males may also pull grass to intimidate subordinates.
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