General information

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 Australia and a dozen or more in New Guinea.  Some of the smaller species, such as Yellow-footed Rock-Wallabies, Burrowing Bettongs, accompanied Pig-footed and Golden Bandicoots, Bilbies and possibly Hairy-nosed Wombats into extinction with the advent of pastoralism. However, the largest species remain in much of their original range with the grey kangaroos expanding inland as grazing habitat increased and coastal habitat was lost in clearance for agriculture. The defining feature of the kangaroo family is that they are the largest vertebrates to hop (both currently and from what we know from palaeontology).

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 Kimberley, Top-End and Far-north Queensland, and the Black Wallaroo (M. bernadus) from Arnhem Land. The Red Kangaroo is the most recently evolved, appearing in the Pleistocene (1-2 million years ago), whereas relatives of the grey kangaroos and wallaroos arose in the Pliocene (4-5 million years ago).  A common feature of this group is that they are grazers.

Species

Eastern Grey Kangaroo (Mainland)

Macropus giganteus giganteus ('giant long-foot')

Best place to see

Mount Ainslie, Canberra, Australian Capital Territory

The bush capital city, Canberra, is the seat of the Commonwealth Government of Australia and has many political and culture attractions. The city of the Australian Parliament is appropriately occupied by Australia's most identifiable symbol, the kangaroo. Mount Ainslie is part of Canberra Nature Park and borders on inner city suburbs. It is accessible by road and walking trails and has a well-habituated population of Eastern Grey Kangaroos. Some conflict exists between people and these peri-urban populations of kangaroos but thus far appreciation and acceptance have outweighed calls for extermination.

Identification

Both the Eastern and Western Grey Kangaroos have a very narrow band of the rhinarium of the nose exposed. The female Eastern Grey Kangaroo is as large but more gracile than the female Red Kangaroo. The fur is long and soft and varies from grey-brown through to dark grey in both sexes. The fur on the abdomen and inner thighs is lighter than the back fur. The forepaws and tips of the hind feet and tail are very dark. The nails on both fore and hind limbs are longer than in Red Kangaroos or Euros and Eastern Grey males tend to have much longer forearms than the aforementioned species. Note the light diamond between the eyes and the light tips to the ears when trying to distinguish this species from the Western Grey. The species is sexually dimorphic with males reaching 70 kg or more and females around 35 kg. However, you cannot reliably distinguish males and females from coat colour although some argue males are a little browner and darker. 

Eastern Grey Kangaroos hop with the back at a higher angle to the horizontal than Red Kangaroos and the forelimbs more extended. The curve and swing of the tail is also more pronounced.

Habitat

Eastern Grey Kangaroo is a woodland, forest edge species grazing out from these havens of dense shelter at night onto short green pastures. The Eastern Grey Kangaroo is probably the most opportunistic and adaptable of all the large kangaroo species. Its range spans latitudes from northern Tasmania to north Queensland and both sides of the Great Dividing Range where it may forage amongst snow. Much of its former habitat has been lost to croplands, which may have exerted some westwards pressure so that it is now found on the eastern margins of the arid rangelands. We also need to recognise that climate has varied enormously over its evolutionary history and no doubt the species has occupied and perhaps dominated the far west of NSW in wetter periods in the past.

Top

Foraging behaviour

Eastern Grey Kangaroos are also primarily grass eaters. They form part of a guild of macropod herbivores which may included wallabies, pademelons, Common Wallaroos and wombats in the eastern part of their range. Microhabitat differences and divergence in dietary preferences reduce potential competition for forage. In the west, they potentially compete with Red Kangaroos, Western Grey Kangaroos and Euros but again microhabitat differences tying the Eastern Greys to dense lateral cover for daytime shelter keep the species somewhat apart.

Eastern Grey Kangaroos prefer short green pasture and and their grazing will contribute to creating grazing lawns which are diverse in species composition and compact creating a strong ground cover. The creation of urban parks and golf courses with clumps of trees and permanent water provides ideal Eastern Grey Kangaroo habitat. Thus they are common in the peri-urban environment and may seen on many country golf fairways.

Reproductive behaviour

The reproductive biology of the Grey Kangaroos sets them apart from the Red Kangaroos and Euros. Development of the offspring is much slower so that young of comparable size permanently exit the pouch at around 320 days compared to 235 in Red Kangaroos and are weaned at 540 days compared to 360 in Red Kangaroos. Breeding is more seasonable with a broad peak in births from October through to March, although this may be more variable in the arid zone.

Eastern Grey Kangaroos do not mate immediately after birth since the oestrous cycle is around 10 days longer than length of pregnancy. They may also mate while they have a young in the pouch, which is about six months old. The resulting embryo remains quiescent (in diapause) due to inhibition of further development while the female is lactating. It is born when the pouch young permanently exits or dies prematurely.

In temperate habitat, a single alpha male has exclusive dominion over a mob of females that may number 30-40 or more. His tenure is typically a single year and competition for the top rank is especially fierce. Females often aggregate with their female relatives so that a group of daughters, mothers, grandmothers and so on may form. This seems to provide greater reproductive success in the younger females but there may be a limit to how large these matrilineal groups can grow as females may produce dispersing sons later in life and stay-at-home daughters earlier on.

The mating system in the arid zone is less well known as groups are smaller, commensurate with the small populations. However, you see very few very large males and so we suspect that these hold dominion but perhaps for more than a single year. Females remain quite faithful to their home range and only extreme drought may cause them to move temporarily so matrilineal groups probably build up over time.

FEastern Grey Kangaroo mothers spend a relatively long period with their young and so offer a good opportunity to observe the affectionate and endearing bond between a mother and her joey. Look out for smaller females nearby, as these may be her daughters.

Social organisation

Eastern Grey Kangaroos are the most social of the kangaroos and so it is rare to see one alone. If you do it is likely to be a male in transit to check out the reproductive status of females in some other part of the mob or a mother with her young-at-foot. One good reason to gather together in a group is that more individuals can be more attentive to possible threats from predators. The chance that someone is looking out when the predator makes its attack increases with group size. Likewise when the group flees, the distraction of many individuals following interweaving paths is greater than a single target fleeing alone. It thus seems odd that mothers with their vulnerable young wander off alone from the mob. The explanation seems to be that the mob is a confusing place for a young-at-foot when potential 'mothers' flee in many directions. Thus mothers remove there immature young-at-foot and train them to retrieve the pouch, if not past permanent exit, or follow closely before again associating with their fellows.

Further readings

Dawson, T.J. (1995). Kangaroos: biology of the largest marsupials. (UNSW Press: Sydney)

Coulson G (1997) Repertoires of social behaviour in captive and free-ranging grey kangaroos, Macropus giganteus and Macropus fuliginosus (Marsupialia: Macropodidae). Journal of Zoology (London) 242, 119-130.