1 Overview

There are three species:

• The Red Kangaroo (Macropus rufus) is the largest surviving marsupial anywhere in the world. Red Kangaroos occupy the arid and semi-arid centre of the continent. A large male can be 1.5 m tall and weigh 85 kg.
• The Eastern Grey Kangaroo (Macropus giganteus) is less well-known than the red (outside of Australia), but the most often seen, as its range covers the fertile eastern part of the continent.
• The Western Grey Kangaroo (Macropus fuliginosus) is slightly smaller again at about 54 kg for a large male. It is found in the southern part of Western Australia , South Australia near the coast, and the Darling River basin.

In addition, there are over 40 smaller macropods that are closely allied to the kangaroos:

• Tree kangaroos are arboreal relatives of the true kangaroo which are found in the dense rainforests of north-east Australia and New Guinea. Several tree kangaroos are endangered, largely because of habitat destruction.
• Wallabies are smaller, usually more thick-set, macropods.
• A wallaroo is a very large wallaby or a small kangaroo.
• Pademelons are small, forest living macropods of around 4 to 6 kg.
• The Quokka is a small wallaby-like macropod of Western Australia.
• Rat kangaroo is a term loosely applied to any of several very small kangaroo-like marsupials, some from the family Macropodidae, some not.
• Kangaroo rats, in contrast, are rodents.

Kangaroos have large powerful hind legs, large feet designed for leaping, a long muscular tail for balance, and a small head. They 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, but they can hop as fast as 70 km/h for short distances.

Kangaroos are herbivores, feeding on grass and roots, and they chew cud. All species are nocturnal and crepuscular, usually spending the days idling quietly and the cool evenings, nights and mornings moving about and feeding, typically in groups called mobs. The life expectancy of a kangaroo is about 18 years.

Kangaroos have few natural predators. One of the major natural predators, the Thylacine, is now extinct. However humans arrived in Australia at least 50,000 years ago, and introduced the Dingo about 5000 years ago. The use of dingoes, and later hunting dogs by Europeans, to hunt kangaroos, has resulted in most kangaroos having an emnity for dogs. The mere barking of a dog can set a full-grown male boomer into a wild frenzy. In extreme circumstances, one or more Wedge-tailed Eagles will attack and sometimes kill a kangaroo (even an adult Red), but only when no more suitably-sized food is available. Goannas and other carnivorous reptiles also pose a danger to the 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, as they do most native populations. Kangaroos and wallabies are apt 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 to drown it.

2 Adaptations

Kangaroos have developed a number of adaptations to a dry, infertile continent and a 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 7 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 9 months (for the Western Grey), before starting to leave the pouch for small periods of time. It is usually fed by its mother until the age of 18 months.

A 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. The composition of the milk produced by the mother varies according to the needs of the joey. In addition, she is able to simultaneously produce two different kind of milk for the newborn and the older joey who still lives in the pouch.

Kangaroos and wallabies have a unique ability to store elastic strain energy in the tendons of their large hind legs. In consequence, most of the energy required for each hop is provided by the spring action of the tendons rather than by muscular effort. There is also a linkage 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 fills the lungs again, 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, a dog, or a human), and also that little 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 quadreped, and the Australian native predators are in any case less fearsome than those of other continents — the benefit is economy: in an infertile continent with very variable weather patterns, the ability of a kangaroo to travel long distances at moderately high speed in search of fresh pastures is crucial.

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 NIH in the USA. The genome of a marsupial such as the kangaroo is of great interest to scientists studying comparative genomics because marsupials are at the right "distance" from humans: mice are too close and haven't developed many different functions, while birds are already too far away. The dairy industry has also expressed some interest in this project.

3 Kangaroos and humans

Unlike many of the smaller macropod species, 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 dingos. There are more, probably many more, kangaroos in Australia now than were present in 1788.

Along with the Koala, kangaroos are regarded as the signature animals of Australia, and are often represented in toys and souvenirs and on the Australian coat of arms. It is part of the logo of Qantas, the largest Australian airline. The Australian national rugby league team is nicknamed the Kangaroos.

Western Grey Kangaroo at Lone Pine Koala Sanctuary , Brisbane

The kangaroo has been historically a staple source of red-meat for native Australian Aborigines. Today, in some areas, kangaroos are culled by licenced professional hunters. Both the meat (which is tasty, tender, and low in fat) and the hides are sold. A small number of animal rights activists and conservationists argue that selective hunting practices (targeting young adult males) has put the population at risk, but there is no evidence of a decline. Some activists have undertaken campaigns to prevent the culling or farming of kangaroos, sometimes using the slogan "Tourist drawcard – Not dead meat". Arguments center on the cruelty of shooting a national emblem. Major conservation organisations, on the other hand, point out that none of the three species of kangaroo is remotely threatened, and focus on the plight of smaller macropods, many of which are threatened or endangered.

Kangaroo meat has been quite successful on the European market, particularly in Germany. It is also processed into dog food. Culling is closely monitored by the RSPCA and state authorities. Kangaroo farming is a substantially more environmentally friendly meat industry than present sheep or cattle farming: kangaroos require less feed than placental stock, are well-adapted to drought, do not destroy the root systems of native grasses in the way that sheep do, and have much less impact on Australia's fragile topsoils. However as of 2004, the traditional regulatory restrictions on the sale of kangaroo meat in the Australian domestic market make kangaroo farming economically unattractive. Nevertheless, the industry is worth around AUD $200 million annually.

Kangaroos are shy and retiring by nature, and in normal circumstances present no threat to humans. Male kangaroos often "box" amongst each other, playfully, for dominance, or in competition for mates. The dexterity of their forepaws is utilized in both punching and grappling with the foe, but the real danger lies in a serious kick with the hindleg. The sharpened toenails can disembowel an opponent, and this is the fate of many dogs that wrestle with a boomer. Boxing kangaroo s (both fist-boxing and kick-boxing) feature prominently in popular culture, especially Bugs Bunny cartoons.

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 greatest threat a kangaroo poses to a human is clearly the danger posed to cars on outback roads. The only reliably documented case of a fatality from a kangaroo attack was New South Wales, in 1936. A hunter was killed when he tried to rescue his two dogs from a heated fray.

4 References

• The Kangaroo Genome Project at Australian National University
• Skippy Size Me 2004 ABC report on kangaroo industry
• Underhill D (1993) Australia's Dangerous Creatures, Reader's Digest, Sydney, New South Wales, BooksEnthsiast.com

Australian animals Macropods

See also Mammalian Embryonic Diapause

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