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

Antilopine Wallaroo

Macropus antilopinus ('antelope-like long-foot')

Best place to see

Litchfield National Park, Northern Territory

Litchfield National Park is within a 2-hour drive from Darwin along a sealed (bituminised road). The Park has many attractions including its waterfalls and natural plunge pools, abundant fauna, rich woodland flora communities including pockets of monsoon forest, and the unusual magnetic termite mounds.  It is amongst the latter that you are most likely to see antilopine wallaroos as they prefer open habitat with short green grasses. The Park is also nominated as the best place to see the Short-eared Rock-wallaby and Agile wallabies are abundant.

Identification

The Antilopine Wallaroo is taller and slimmer than the other Wallaroos (black and common) and more closely resembles Red and Grey Kangaroos although it retains the bare muzzle skin pattern typical of wallaroos. Large males have a characteristic swelling of the nose behind the nostrils giving them a distinctive profile and probably a greater nasal surface for heat loss by evaporative cooling in a constantly hot climate. Males are easily distinguished from females as they have a reddish tan coat with a much paler front and inner surfaces of the limbs. Females are more variable in colour ranging from grey to a light tan and share the characteristic of pale undersurfaces. The coat is typically shaggy and coarse as characteristic of the wallaroos. Sexual dimorphism is pronounced with males exceeding 70 kg and females rarely as large as 30 kg. 

Habitat

The Antilopine Wallaroo inhabits savannah woodlands across the wet-dry tropics of northern Australia. The population is contiguous between the 'Top End' of the North Territory and the Kimberley of Western Australia but a disjunction occurs at the southerly point of the Gulf of Carpentaria to another eastern population on Cape York. The latter is not genetically differentiated from the western population. Antilopine Wallaroos may be found on the slopes and tops of small hills and in the valleys and low-lying depressions down to the floodplains of major rivers. They tend to avoid steep slopes occupied by the Northern Wallaroo and may retreat seasonally into higher country when floodplains are inundated in the Wet season (monsoon). They will concentrate in large groups on open moist depressions with short green grass, especially that re-shooting after fire, in areas also favoured by large mound building termites. On such sites densities can reach as high as 30 Wallaroos per square kilometre. Recent research on factors affecting their density across the whole of their northern Australian range suggests they favour sites with permanent water (given seasonal aridity in the Dry) and may be advantaged by late season fires (August - November) stimulating green pick. The latter is contrary to small mammals and birds that decline with a high frequency of late season fires due to loss of cover and a simplification of habitat. In north Queensland, the density of Antilopine Wallaroos is inversely related to that of Eastern Grey Kangaroos suggesting competition or small scale variation in habitat choice.

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Foraging behaviour

On limited data, male Antilopine Wallaroos have large home ranges of 100 hectare (ha) or more whereas females occupy small ranges of < 20 ha. Typical dry season behaviour is to rest as groups in the shelter of trees during the day and commence grazing near dusk, retiring to shelter around dawn. Grazing during daylight may be extended in the Wet season under cooler heavy overcast but shelter is sought with heavy rain. Their diet comprises a high proportion of grasses and they favour areas where grasses are short like low tussock grasses or tall grasses reduced to shoots by fire.

Reproductive behaviour

Antilopine Wallaroos tend to breed seasonally with pouch young permanently emerging at the commencement of the wet season. The do not have a post-partum mating and it is unknown whether they retain a diapausing blastocyst. Thus females may enter a seasonal anoestrus so that one offspring is produced per year at the optimal period new grass growth with the advent of the monsoon. However, other observations suggest an increase in male fighting and mate guarding following the permanent emergence of pouch young and so mating is likely to occur soon after. Limited evidence suggests a quite long oestrous cycle of 40 or more days without birth and a gestation length of around 35 days. Thus if first matings after permanent pouch exit largely do not lead to conception then births would tend to be concentrated in March-April as observed with permanent pouch exit at around 270 days in December-January. Male sexual behaviour is typical of the large kangaroos with the largest males dominating in sexual encounters to the possible exclusion of smaller males into peripheral habitat. Males insert their nose into the female's urine stream and thus may engage in flemen to aspirate some of this urine onto oestrogen receptors in the vomeronasal organ. Males and females may segregate during the dry season when there is a higher incidence of male or female only groups relatively to the typical mixed sex groups of the dry.

Social organisation

Antilopine wallaroos are gregarious and typically form groups of three or more individuals. Very large aggregations may occur on short green pastures. Unlike other large kangaroos, allogrooming (the grooming of one individual by another) is common between males and females, and between the sexes and not necessarily associated with sexual behaviour. The associations between individuals are relatively fluid and there is not evidence of closed social grouping in common with other large kangaroos. A single male Antilopine was radio-tracked through the Wet season and occupied a home range of 76.1 ha moving over several ridges, slopes and valleys. In the same habitat a frequently sited female ranged over 14.2 ha and avoided the ridges and a large male had a diffuse home range of 102.3 ha. All individuals avoided inundated areas of the Adelaide River floodplain and dense stands of native sorghum (speargrass).

Further readings

Croft DB (1987) Socio-ecology of the antilopine wallaroo, Macropus antilopinus, in the Northern Teritory, with observations on sympatric M. robustus woodwardii and M. agilis. Australian Wildlife Research 14, 243-255.

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

Ritchie EG (2005) Ecology and conservation of the Antilopine Wallaroo. Nature Australia Summer 2005-2006, 26-31.