Kangaroos are marsupials and belong to the Family Macropodidae (i.e. big feet) that is grouped with the Potoroidae (potoroos, bettongs, rat-kangaroos) and Hypsiprymnodontidae (musky rat-kangaroo) in the Super-Family, Macropodoidea. This comprises around 50 species in
The species commonly called the ‘kangaroos’ are the result of an arbitrary division of the Macropodidae based on a hind foot longer than 250 mm. The kangaroos then comprise six species of which the best known are the Red Kangaroo (Macropus rufus) of the arid heartland and the
Eastern Grey Kangaroo (M. giganteus), the latter being Skippy's species. The
Eastern Grey Kangaroo has a broad latitudinal distribution up the eastern part of Australia from northern Tasmania to Cape York. Its close relative, the
Western Grey Kangaroo (M. fuliginosus) has a southerly and westerly distribution form western NSW and Victoria through South Australia to Western Australia. The Common Wallaroo has the broadest geographic distribuion of the kangaroos and forms a cline of subspecies across the continent but wallaroos are not found in Tasmania. The remaining two kangaroo species are less well-known and include the
Antilopine Wallaroo (M. antilopinus) from the
Macropus rufus ('red long-foot')
Sturt National Park, New South Wales
Sturt National Park is in the far north west of NSW at the boundary between NSW and Queensland to the north and South Australia to the west. The largest wildlife management structure in the world, the Dingo Fence, forms the state boundaries. Sturt National Park is a quintessential sample of the Australian outback with grassy stony (gibber) downs, saltbush plains, mesas (jump-ups) and red sand dunes. Here you will find the largest Red Kangaroos on the continent in a region with some of the highest densities of this species. As a bonus you can also see Eastern and Western Grey Kangaroos and Common Wallaroos (Euros) on the Park. However this brings a challenge in identification for the novice, as the common names are confusing. Most female Red Kangaroos are in fact blue-grey, Eastern Grey Kangaroos are grey through to brown and Western Grey Kangaroos are dark grey through to black. Common Wallaroos, of which the Euro is a sub-species, are grey, grey-brown, dark grey or even black. The Park has about 6 frog species, around 140 bird species including the rare Grey Falcon, and is particularly diverse in reptiles with 56 species of lizards and snakes. The Park is about 3.5 hours drive from Broken Hill which is a major regional centre with air and rail services to Adelaide and Sydney.
Colouration of Red Kangaroos is not uniform. The abdomen and lower parts of the limbs are light grey to white but the nails of the feet and forepaws are black. The tail tip is always a light ochre colour that clearly distinguishes it from the black-tipped tailed of Grey Kangaroos. Red Kangaroos hop with their back almost parallel to the ground and their head low.
Red Kangaroos are found throughout the Outback and are both the most abundant and most commonly encountered species. They prefer open, sparsely treed habitat and find adequate shelter at the base of large shrubs but may move into acacia thickets and the trees along the margins of creeks during the height of summer. They prefer short green grass or winter forbs (small annual dicotyledons) for forage and thus are most often found on run-on zones (e.g. flood plains of creeks and terminal parts of drainage channels). However, they may move onto higher stony ground after rain to avoid the boggy clay soils. Their geographic range is generally within the arid zone; i.e. the central area of Australia with an annual rainfall of 250 mm or less in the southern part and 500 mm or less in the more monsoonally influenced north. Although Red Kangaroos can cope with the extreme high (and low) temperatures of the arid zone and the low availability of water, they tend to evade drought by travelling to areas favoured by local and patchy thunderstorms and so their mobility is a feature of their adaptations to the arid zone.
The first preference of Red Kangaroos is green grass, followed by green forbs and mature grass. Grass can provide bountiful energy, but it is tough to digest. Thus anatomical and physiological adaptations have evolved to exploit this abundant food source, and these parallel similar adaptations in sheep, goats, deer and antelope. All the kangaroo species have a specialised dentition to crop grass, and progressively wear out and shed their pre-molars and then molars as the silica in grass abrades their teeth. They have large and complex fore-stomachs where they garner the assistance of specialised bacteria and a few protozoa and fungi to break down plant fibre in a fermentative chamber. They gain about 70% of the available energy in the process and digest the end-products, short-chain fatty acids.
Red Kangaroos feed selectively amongst the pasture, nipping off grass blades or small forbs with incisors at the front of a small delicate mouth. They can push aside shrubs with their manipulative forepaws to get out small green plants growing in the protective shade. During drought they more move up to 50 km to a local rain shower to feed on ‘green pick’ but, at least mature females, return to their normal home range after widespread rain. Only young males and some young females disperse over long distances.
Female Red Kangaroos become reproductively mature at around 18-24 months and males at about 36 months. However, males compete with each other to mate with females and so only reach a competitive size at about 7 years and are in their prime at around 10 years.
There is no breeding season for Red Kangaroos. The only time that females may be in synchrony is after the breaking of a long hard drought. Typically females have a production line of overlapping generations. The oldest is a ‘young at foot’ that has permanently left the pouch but is still dependent on a drink of lipid-rich milk from an elongated teat in its mother’s pouch. It will be finally weaned at about 12 months age. The pouch is reserved by a smaller unfurred sibling of the next generation, who grips a second teat and suckles on milk more balanced in carbohydrates, proteins and lipids as suits its age. Unformed in the mother’s uterus is a third generation sister or brother, waiting for a pouch vacancy. When that is imminent, its development is renewed but it is born in an embryonic form little resembling its final body shape. This birth triggers oestrus (receptivity to a male’s mounting attempts) in the mother who has attracted a bevy of competing males from which the largest will emerge as consort. If not, then the female may seek out large males as a potential partner ensuring the ‘best genes’ for her offspring.
As is the way with marsupials, development is relatively slow through nourishment of the young by lactation rather than a placenta. Kangaroos overcome this limitation by overlapping the generations to speed recruitment into the population. Even so, most young will die through inadequate high quality forage in the unpredictable and unproductive arid zone and, though equal numbers of sons and daughters are produced, male mortality is higher and populations are female-biased. Populations boom in a run of good years and then crash with a hard drought.
F You should watch mothers, particularly those with large pouch young in the late afternoon. At this time you may see the first unsteady excursions of the young as it overbalances or is dumped out of the pouch. As they gain coordination, they play around the mother, hopping in quick excursions from her as a safe base, and sometimes returning to briefly batter her head in play.
F If you see several males in the vicinity of a female who all seem intent on keeping her in close range then you will be in for an interesting insight into mating behaviour. You should note the largest male positioning himself as consort and stroking the base of the female’s tail to test her readiness to mate. Other males may challenge him and the female may hop off with a trail of importunate males in tow.
Males often approach a female and sniff her cloaca. In fact, they do more and gently nudge it with their nose stimulating a reflex to urinate (useful when they were residents of their mother’s pouch so that she could remove their waste). They then aspirate a little of this urine stream into a specialised nasal cavity (the vomeronasal organ) which has receptors for oestrogen. Thereby the male can test a female’s likelihood of oestrus.
Young Red Kangaroos may disperse from their natal area by a hundred or more kilometres but adults typically remain in home range of around 1.5 square kilometres. They do not use these ranges exclusively but overlap with individuals of both sexes and different age classes. No permanent groups are formed but rather individuals aggregate in loose associations around shelter, forage or water. They are more often within 50 m of another kangaroo than alone but only mothers and their young-at-foot or oestrous females and their consorting male keep close proximity.
You may see a female, her joey and an accompanying male and think they are a family group. In reality the female’s three generations of young may each have a different father although the most powerful male (the alpha male) in her home range will typically mate with half the females, more than any other male. He needs to conserve some of his energy to maintain dominion over two or three years since a drought could wipe out any of his offspring in a given year.
Males move through their local population of females, regularly checking their oestrous status. Those with very large pouch young are most attractive since permanent pouch exit is the cue for birth and a post-partum oestrus. However, death of a pouch young could equally trigger these events so males are always checking.
Croft DB (1981) Behaviour of red kangaroos, Macropus rufus (Desmarest, 1822) in northwestern New South Wales, Australia. Australian Mammalogy 4, 5-58.
Dawson, T.J. (1995). Kangaroos: biology of the largest marsupials. (UNSW Press: Sydney)