A kangaroo is a marsupial from the family Macropodidae.
In common use the term is used to describe the largest species
from this family, the Red Kangaroo, the Antilopine Kangaroo, and
the Eastern and Western Grey Kangaroo of the Macropus genus. The
family also includes many smaller species which include the
wallabies, tree-kangaroos, wallaroos, pademelons and the Quokka,
some 63 living species in all. Kangaroos are endemic to the
continent of Australia, while the smaller macropods are found in
Australia and New Guinea.
In general, larger kangaroos have adapted much better to changes wrought to the Australian landscape by humans, as many of their smaller cousins are endangered. However there is considerable controversy over farming of kangaroos for meat.
The kangaroo is an Australian icon: it is featured on the Australian Coat of Arms, on some currency, and is used by many Australian organisations, including Qantas.
The word kangaroo derives from the Guugu Yimidhirr word gangurru, referring to a grey kangaroo. The name was first recorded as "Kangooroo or Kanguru" on 4 August 1770, by Lieutenant (later Captain) James Cook on the banks of the Endeavour River at the site of modern Cooktown, when HM Bark Endeavour was beached for almost seven weeks to repair damage sustained on the Great Barrier Reef.
A common legend about the kangaroo's English name is that it came from the Aboriginal words for "I don't understand you." According to this legend, Captain James Cook and naturalist Sir Joseph Banks were exploring Australia 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.
Kangaroo soon became adopted into standard English where it has come to mean any member of the family of kangaroos and wallabies. Male kangaroos are called bucks, boomers, jacks, or old men; females are does, flyers, or jills, and the young ones are joeys. The collective noun for kangaroos is a mob, troop, or court. Kangaroos are sometimes colloquially referred to as roos.
A Tasmanian Forester (Eastern Grey) Kangaroo in motion.There are four species that are commonly referred to as kangaroos:
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 travelers tales for quite sometime.
Kangaroos have large, powerful hind legs, large feet adapted
for leaping, a long muscular tail for balance, and a small head.
Like all marsupials, female kangaroos have a pouch called a
marsupium in which joeys complete postnatal development.
Kangaroos are the only large animals to use hopping as a means of locomotion. The comfortable hopping speed for Red Kangaroo is about 20–25 km/h (13–16 mph), but speeds of up to 70 km/h (44 mph) can be attained, over short distances, while it can sustain a speed of 40 km/h (25 mph) for nearly two kilometers. 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.
Because of its long feet, it cannot walk normally. To move at slow speeds, it uses its tail to form a tripod with its two forelimbs. It then raises its hind feet forward, in a form of locomotion called "crawl-walking."
The average life expectancy of a kangaroo is about 4–6 years, with some living until they are about 23.
Different species of kangaroos eat different diets. Eastern grey kangaroos are predominantly grazers eating a wide variety of grasses whereas some other species (e.g. red kangaroos and swamp wallabies) include significant amounts of shrubs in the diet. 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, kangaroos have developed specialized 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.
Despite having a very similar diet to cows, kangaroos produce virtually no methane from digestion. 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, as methane is a greenhouse gas 23 times more powerful than carbon dioxide.
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. The mere barking of a dog can set a full-grown male boomer into a wild frenzy. 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 dingoes and other canids, introduced species like foxes and feral cats also 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. Another defensive tactic described by witnesses is catching the attacking dog with the forepaws and disemboweling it with the hind legs.
Kangaroos have developed a number of adaptations to a dry,
infertile continent 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. 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
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 there has been enough rain to produce a large quantity of green vegetation.
Kangaroos and wallabies have large, stretchy 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. This is true in all animal species which have muscles connected to their skeleton 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 that, 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 that 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 continents—but economy: in an infertile continent 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.
A sequencing project of the Kangaroo genome was started in 2004 as a collaboration between Australia (mainly funded by the state of Victoria) and the National Institutes of Health in the US. 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 haven't developed many different functions, while birds are genetically too remote. The dairy industry has also expressed some interest in this project.
This Kangaroo Page is Copyright The Animal Web Guide © 2004 - 2009 Chuck Ayoub