Eastern Grey Kangaroo (Macropus giganteus)
The Kangaroo is recognized all over the world as an Australian icon.
Looking kind of like a cross between a big bunny rabbit and a furry deer, the Eastern Grey is one of three species of Kangaroo, and the one most likely to be seen close to the east Coast.
Here at Billabong Sanctuary we have several families of these gentle animals roaming free in the park. Grab a bagful of seed from the kiosk, start walking down any of the paths, and you will soon have a friendly Roo eating out of your hand. If you are lucky, baby joey might peek out of mama’s pouch for a nibble as well.
What’s in a Name?
Kangaroos belong to the family Macropodidae, a group of marsupial mammals with huge hind feet. They range in size from tiny wallabies to enormous kangaroos, all with the same general body form.
The genus name Macropus is derived from the Greek words for long and foot, and the species name giganteus quite obviously means very big. So the scientific name of the Gray Kangaroo simply means ‘a very large animal with long feet’.
The word ‘Kangaroo’ comes from an Aboriginal word. It is said that Captain Cook gave it this name upon seeing it near the site of the present day Cooktown in northern Queensland.
Grey Kangaroos are sometimes known locally as Foresters, Scrub Kangaroos, or simply Scrubbers.
What do They Look Like?
All members of the Macropod family have a characteristic pear-shaped body with a relatively small head, enormous back legs, shortened front legs, and powerful tails.
There are 5 well-developed toes on the front feet; there is no opposable digit, but the front paws are very much like hands, and are used for holding food. The back feet have four toes, but the inner two are fused up to the claws. (This feature is called 'syndactyly'.) The double claw at the end is used for grooming. The central claw on the hind foot is long and powerful, and is used as a weapon in aggressive and defensive attacks.
Eastern Grey Kangaroos have soft grey to pale brown fur. Compared to Red Kangaroos, they have smaller ears, pointier snouts and more evenly coloured fur. (Red Kangaroos have white streaks on their snouts, and white fur on their underparts).
Eastern Grey Kangaroos are the second-largest of Australia’s marsupials. (A marsupial is a pouched mammal). An adult male stands taller than a grown man, and can weigh up to 66 kg (145 lb). Total length of the head and body averages well over 2 m (6 ½ ft) with nearly half of this being the length of the tail. Females are smaller, reaching a maximum weight of about 32 kg (70 lb).
The Western Grey (Macropus fuliginosus) is the third Kangaroo species. It has brown fur, and is slightly smaller than the Eastern Grey. It is found in southern parts of Western Australia and South Australia, as well as NSW Victoria and southern Queensland where its range overlaps that of the Eastern Grey.
Where do They Live?
Eastern Grey Kangaroos live throughout most of the eastern states of Australia, including Tasmania, in areas with more than 250 mm (10 in) of average annual rainfall.
They are found in a variety of habitats, from semi-arid mallee scrub through woodlands to forested areas.
(Mallee are eucalyptus shrubs which grow in dry areas with poor soil.)
A group of Kangaroos (called a mob) is usually made up of one dominant male, several adult females, and both male and female juveniles. Several mobs may graze together, in aggregations of up to 100 animals.
Mobs of kangaroos travel long distances and easily get past artificial barriers such as stock fences.
Coping with the Heat
Summers in the interior of Australia are intensely hot; daytime temperatures often reach well over 40 degrees C (105 F). Kangaroos rest under trees or shrubs during the heat of the day, and come out to feed in the cool of the evening and at night.
Kangaroos can’t sweat when they are hot, as people can. Instead, they lick their chests and the insides of their forearms till the skin is quite soggy. The blood vessels in these areas are close to the surface of the skin. When the moisture evaporates, it cools the blood circulating underneath, which helps to cool down the whole animal.
This evaporative cooling is the same principle as that used in air conditioners!
Kangaroos have long, thick eyelashes that help to protect their eyes from the glare of the sun.
Poetry in Motion
When travelling fast, the Kangaroo bounds forward on its huge, powerful hind legs, with the tail held out behind for balance, and the front legs tucked in close to the body. This motion is very fluid and graceful, and the Roo can cover huge distances, with massive leaps up to 8 m long (26 ft), and short bursts of speed reaching nearly 65 kph (40 mph)! An average travelling speed would be about 12 kph (8 mph).
When Kangaroos are moving slowly, or feeding, they balance on their small front legs and tail, swing their hind legs forward like a pendulum, then bring up the tail and front legs to complete the movement. The muscles of the hind legs are attached in such a way that when travelling on land, the Kangaroo always moves both limbs together. Interestingly, if the Kangaroo ever has occasion to swim, it can then move its hind legs separately.
With these strong hind limbs, the Kangaroo can jump vertically from a standing start over obstacles as tall as itself. Females with a large joey in the pouch can bound at top speed up a near vertical slope.
Male Kangaroos also use their tail to balance when they rise up on their hind legs and have 'boxing matches' with other males. They tip back their heads and swat at each other with their long front claws, or kick out with their strong back legs, armed with that powerful central claw. When one male backs down, the other will stop attacking. They may then casually scratch themselves, and resume feeding.
What do They Eat?
Eastern Grey Kangaroos eat mostly green grass as well as some other types of herbage, feeding mainly at night. They can live for long periods without water, utilizing the moisture in their food.
Adaptations for this Diet
This plant diet is high in cellulose. In common with other animals, Kangaroos lack digestive enzymes to break down cellulose, so they have evolved both mechanical and chemical means of extracting nourishment from their food.
Grass is nipped off with the front teeth (incisors) which grind against a hard plate at the top of the mouth. There is a gap (called a diastema) between the front teeth and the back teeth (molars). This gives the tongue more room to push the food about inside the mouth and to position it between the molars for grinding.
The molars have sharp grinding surfaces. As the animal grows, the molars erupt in succession, with the one in front dropping out, and the ones behind moving forward to take its place. This way there is always a sharp new cutting surface to break down the plant matter.
The stomach is divided into two parts: the sacciform and the tubiform. In the front part, shaped like a large sack, are millions of microscopic organisms, mainly bacteria but also fungi and protozoa. These microbes ferment the plant matter, releasing nutrients that the Kangaroo can use.
Food may stay in this forestomach for up to 16 hours while fermentation takes place. The Kangaroo sometimes coughs up an undigested bit of food, and chews it some more before re-swallowing it. This is similar to a cow chewing its cud.
Once fermentation is well underway, the partially digested food passes into the second, tube-shaped part of the stomach, where acids and enzymes secreted by the Kangaroo complete the process of digestion.
Breeding and Birth of the Young
The reproductive biology of the Kangaroo is unusual and amazing, for several reasons.
The most well-known, of course, is that most of the development of the young takes place not in the womb, but in an external pouch.
The female is often nurturing young at three entirely different stages of development, even producing milk of different composition in different teats.
In addition, development of the youngest embryo can be turned on or off, depending on external conditions.
Here is the story:
The female Grey Kangaroo may come into season at any time of the year, but most births occur in the summer. To check if she is ready for breeding, males will approach and sniff the area around the base of her tail. They may also smell her urine.
If the female is nearing the stage when she will be receptive to breeding, the male will start to follow her closely, sometimes grasping and stroking her tail. The dominant male of the mob will eventually be allowed to breed, with mating lasting up to 50 minutes.
The young is born about 36 days after mating. To get ready for the birth of the joey, the female will lick the pouch clean and lean up against the base of a tree, resting her hindquarters on her tail behind her.
The baby Kangaroo is hairless and tiny, barely the size of a peanut, and weighing only about 800 mg (< 0.03 oz). Nevertheless, it leaves the birth canal and makes its way into the pouch unassisted by the mother. This journey takes about 15 minutes-- an amazing task for such a minute, sightless creature, using only rudimentary forelimbs to claw its way upwards.
Once inside the pouch, the miniature joey attaches itself to one of the 4 teats. It will suckle exclusively from this one teat until it is weaned.
Unlike Red Kangaroos, which mate again soon after birth, the Grey Kangaroo will only mate again if she loses the joey in her pouch, or later on, when the developing joey is about 4 months old, if food supplies are plentiful. She will retain this embryo until the joey leaves the pouch.
Raising the Young
While the very young joey is developing inside her pouch, the mother will continue to lick the pouch clean, and will consume the joey's waste products.
The joey remains attached to the teat for 120 to 130 days, during which time its body remains pink and naked, and its eyes are closed.
At about 100 days the joey starts to move its limbs inside the pouch. By about 186 days its eyes have opened and it peeks out of the pouch for the first time.
Growth over the next 40 days or so is rapid; the limbs start to develop and often stick out of the pouch. The mother starts to groom the joey, and it starts to sniff at her head and at its surroundings. As she leans close to the ground to feed, it can lean out of the pouch to take its first taste of grass or other plants.
By about 9 months, the joey and will emerge from the pouch for the first time, usually by toppling out. At first it will remain in the open air for only a minute or two, then quickly scramble back into the safety of the pouch.
To climb back into the pouch, it kicks with its hind legs and does a complete somersault, ending up with it head facing the opening. The mother can control the joey's exit and entrance from the pouch by relaxing or contracting the muscles around the opening.
For the next few weeks the joey will start to make progressively longer excursions away from the mother, returning quickly to be groomed or to suckle.
The joey will not permanently vacate the pouch till about 11 months old. It remains close to its mother, continuing to suckle by sticking its head into the pouch for the next 7 or 8 months or so.
Meanwhile the dormant embryo has developed and a second newborn joey has entered the pouch and attached to one of the other teats. At this stage the mother actually produces two different types of milk! The milk in the teat used by the newborn joey is much lower in fat and higher in protein than the milk in the teat used by the joey at heel.
The young joey is weaned at about 18 months of age. Even when the mother no longer allows it to suckle, it often remains in close association with her until it reaches sexual maturity.
Eastern Grey Kangaroos mature at about 4 years of age, and females mature at about 18 months of age.,
Eastern Grey Kangaroos can live for up to 18 years in the wild.
Status in the Wild
There are millions of Grey Kangaroos in mainland Australia and their status is secure. In Tasmania, the population is considered to be at risk.
In fact, because of their perceived status as pests to graziers and farmers, hundreds of thousands of Kangaroos are legally culled every year in New South Wales, Queensland, South Australia and Western Australia.
Problems apparently caused by Kangaroos are listed by graziers and farmers as competition with livestock for food and water, and damage to fences and crops.
The Kangaroo cull is undertaken by licensed shooters, following strict guidelines, on a quota basis. Quotas are set every year based on aerial surveys of the Kangaroo population.
Nationwide, the 2007 quota for all three species of Kangaroo was set by the Department of the Environment at about 3 ½ million animals. This is only about 15% of the estimated total population size for all Kangaroos on the mainland. In other words, there are estimated to be over 23 million Kangaroos in Australia!
Hides and/or meat are harvested and sold after the animal is shot.
Quotas are rarely met in any given year.
There are few non-human predators on Grey Kangaroos. Dingoes are probably the most significant, while foxes and wedge-tailed eagles can take young animals.
Because Kangaroos are closely monitored and managed by wildlife officials, and because of their importance as our national symbol, as well as the economic value of their hides and meat, it is unlikely they will ever become endangered.
Generations to come will be able to see these friendly, furry faces peeking up out of the scrub.