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

Western Grey Kangaroo (Mainland)

Macropus fuliginosus melanops ('sooty long-foot')

Best place to see

Gawler Ranges National Park, South Australia

The Gawler Ranges National Park is 163,500 ha of ancient volcanic rocky hills with some old dune ridges in the southern part. The Park has few services and so provides a wilderness experience with a high degree of self-sufficiency required by visitors. The habitat is diverse and includes dramatic gorges and bluffs and spinifex grassland. The flora (225 species) and fauna (18 mammals, 126 birds, 33 reptiles, 3 frogs) are likewise diverse. Amongst the mammals, yellow-footed rock-wallabies can be seen as well as the Western Grey Kangaroo. The Park is about 6 hours drive north-west of Adelaide off the Eyre Highway.

Identification

Western Grey Kangaroos might perhaps be better called Southern Grey Kangaroo as their distribution extends across southern Australia from western Victoria and NSW, south-western Queensland to the mid-latitudes of Western Australia. There is a zone of overlap with Eastern Grey Kangaroos in the eastern part of this distribution and the two species were not separately distinguished until the 1970s. Western Grey Kangaroos show all the same characters of their Eastern counterparts that enable you to distinguish them from Red Kangaroos or Euros. Thus the problem where they overlap is how to tell an Eastern and Western Grey Kangaroo apart. The Western Grey is typically a little stockier and much darker. Its fur may grade from a dark chocolaty brown to almost black but with lighter underparts. The diamond between the eyes is typically dark as are the tips of the ears. Their head is a little more solid. There can be no confusion between grey kangaroo species in the western part of their range through South and Western Australia as this is beyond the zone of overlap.

F The sexes differ in size in a similar range to Eastern Grey Kangaroos but the mature males have a distinctive curry-like odour. This has lead to the common name of 'stinker' in some parts and an aversion to killing this species for human consumption.

Habitat

Western Grey Kangaroos tend to be in the more shrubby areas and Eastern Grey Kangaroos on the grassland. Typical habitat is scrub or mallee in the heart of their range in South and Western Australia . This vegetation type has been extensively cleared for cropping and thus Western Grey Kangaroos have lost extensive habitat in persist in the wheat lands only in remnant patches of woodland. They may forage out of these remnants into the crops and thus are blamed for crop damage. However, extensive research in the wheat belt of Western Australia suggests this damage is minimal as Western Grey prefer native grasses with some browse. Populations in remnants can be remarkably stable and self-regulating. The loss of mallee and woodland habitats is likely to have precipitated some northwards expansion of the Western Grey Kangaroo's range into the arid rangelands. The expansion into north-western NSW appears to have coincided with a La Nina event in the 1970s leading to very high rainfall and the possibility for this species to move up through river systems and expand out along tributaries. The persistence of the species in the arid zone is ascribed to the provision of water for livestock as the species has a higher water demand than more arid-adapted Red Kangaroos (but much less than sheep or cattle). This 'anomalous' presence in the rangelands has lead to some demand for extirpation with claims the species had never previously been there. This is a very myopic view as grey kangaroos have been around for a couple of million years and the large variation in climate and associated habitats across inland Australia  over these many millennia have no doubt favoured these species at times. Rather the entry and persistence of grey kangaroos in the arid rangelands is an expression of their adaptability and capacity to find 'a new home' when former habitat is clear-felled and homogenised.

Of these  'refugees', Western Grey Kangaroos are more abundant than Eastern Grey Kangaroos in the arid rangelands where the species overlap. In both western NSW and northern South Australia there is some concern that they are 'taking over' from Red Kangaroos. This is likely the result of selective shooting for the human consumption market where Red Kangaroos are favoured as the meat is untainted by a distinctive smell.

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Foraging behaviour

All the large kangaroos are grazers with a preference for summer grasses and winter forbs (small herbs) where they overlap in the sheep rangelands of Western NSW. Thus there is potential for dietary competition between the species. Different micro-habitat preferences tend to segregate the species with Red Kangaroos predominantly in the most open and treeless plains, Euros in the hills, Eastern Grey Kangaroos in the riparian strip along major creeks and drainages, and Western Grey Kangaroos amongst tall shrubs and acacia thickets. Of the four species, the Western Grey Kangaroo takes the most shrub and browse. Grey kangaroos, especially males, have relatively long fore-arms compared to the Red Kangaroo and Wallaroos. A large male Western Grey Kangaroo with a height approaching two metres and a reach of another half a metre can easily browse on low acacias like the Elegant Wattle (Acacia victoriae) and are regularly seen to do so. As browsing increases this wattle produces larger spines as a deterrent to mammalian herbivory. This interaction, akin to Gerenuk (a long-necked browsing antelope) on the African savannahs, suggests browsers did not fully disappear with the extinction of megafauna many thousands of years ago. The capabilities of the Western Grey Kangaroo, which like some of the large browsing kangaroos of the past is relatively short-faced, has been overlooked in a general model that the extant fauna is solely grazers.

In grazing trials in Western Australia, Western Grey Kangaroos will browse acacia seedlings but tend to avoid species with high tannin content like Eucalypts. More grass-like species (e.g. Allocasuarina, Viminalia, Xanthorrhoea) were preferentially browsed down. Selection of forage in Western Grey Kangaroos was towards high energy content with avoidance of tannins and high salt loads. Nitrogen (protein) is rarely limiting in their diet.

Reproductive behaviour

The reproductive biology of Eastern and Western Grey Kangaroos is very similar. However, Western Grey Kangaroos do not show diapause and so only have two dependent generations of young (one in the pouch and one at foot). The pouch must be permanently vacated for the female to mate again.

Western Grey Kangaroos in the woodland refuges in the WA wheat belt, show a decline in fertility from about 8 years so that few 12-year-old females breed. Population sizes may thus remain very stable but the generality of these results to other parts of the range is not known.

Social organisation

Females and their kin are the core of the mob as in Eastern Grey Kangaroos. Males may segregate into different areas during the non-breeding period but this has not been well studied in the arid zone. The Western Grey Kangaroo seems to have an undeserved poor reputation amongst pastoralists who may refer to them as 'black bastards'. However, their behaviour is as equally fascinating as the other three species and their resilience has been proven by their persistence in small woodland refuges amidst broad-acre crops.

Further readings

Arnold GW, Weeldenburg JR, Ng VM (1995) Factors affecting the distribution and abundance of western grey kangaroos (Macropus fuliginosus) and euros (M. robustus) in a fragmented landscape. Landscape Ecology 10, 65-74.

Arnold GW, Steven DR, Weeldenburg J (1989) The use of surrounding farmland by western grey kangaroos and their impact on crop production. Australian Wildlife Research 16, 85-93.

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

Parsons MH, Lamont BB, Davies SJJF, Kovacs BR (2006) How energy and coavailable foods affect forage selection by the western grey kangaroo. Animal Behaviour 71, 765-772.