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

Black Wallaroo

Macropus bernadus ('Bernard's long-foot')

Best place to see

Kakadu National Park, Northern Territory

The Black Wallaroo is most likely seen at the base or slopes of the Arnhem Land escarpment around the East Alligator ranger station and Nourlangie Rock. In the popular tourism period of the Dry season (May-September), the Black Wallaroo may be seen drinking at springs at the base of the escarpment and perhaps on road and track verges if they retain short green vegetation. However, it is most likely to be active only around dawn and dusk and throughout the night. In the Wet season, Black Wallaroos may be visible on heavy overcast days but accessibility to its habitat may be a problem as a result of flooding.

Identification

The Black Wallaroo is the smallest member of the kangaroos. The common name refers to the colouration of the males which vary from dark sooty-brown to black and not the females that are pale grey to grey-brown. This may lead to confusion with the northern sub-species of the Common Wallaroo (Macropus robustus woodwardii) which has similar body form and colouration to at least the female Black Wallaroo and shares habitat on the Arnhem escarpment. The distinguishing feature of the Black Wallaroo is its short ears and it is about three times more abundant than the Common Wallaroo on the Arnhem Land plateau.  

Habitat

The Black Wallaroo has the most restricted habitat of the kangaroos and is only found in a small area of western and central Arnhem Land. This is an area of steep rocky escarpments and the tops of a deeply dissected plateau that arises abruptly to the east of the floodplains that form most of Kakadu National Park. In the Park, the Black Wallaroo is found on the sandstone escarpment and plateau of Arnhem Land and at some outliers including Nourlangie Rock and Mt Brockman. It inhabits all the main vegetation associations - sandstone monsoon forest, sandstone eucalypt woodland and forest, and sandstone spinifex. Monsoon forest and spinifex sites may have large areas of bare rock and the Black Wallaroo is most likely to be seen in the monsoon forest association even though this habitat is relatively sparse.

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Foraging behaviour

Little is known of the behaviour of Black Wallaroos but the diet has been estimated from macroscopic and isotopic analysis of the faecal pellets (scats). The first method is a examination of the crushed faecal pellet under a dissecting microscope and was used to distinguish the relative amounts of grass seed, browse seed (i.e. seed from herbs and shrubs) and fruit skin. The second method used a mass spectrometer to estimate the ratio of two isotopes of carbon ¹²C and ¹³C. The ratio of ¹³C/¹²C is expressed relative to a standard and not a simple proportion and so is negative - -9 to -17 parts per thousand for grass and -22 to -32 parts per thousand for browse and forbs (small herbaceous plants). Black Wallaroos were estimated to eat about 75% grass in the Dry season and 93% grass in the Wet season. Thus they are occasionally seen along the verges of roads and tracks near the base of the escarpment where grasses may be found. Even so they do eat plants specialised to grow on rocks like Ficus  and consume more browse than the larger Common (Northern) Wallaroo in the same habitat but less than rock-wallabies. It is usually not active in the day but may be seen foraging on heavy overcast days during the Wet season (northern Australia monsoon from December to March). For most of the day it takes shelter in the rocks, crevices and trees of the escarpment. The best chance to see Black Wallaroos is when they come down to springs at the base of the escarpment to drink especially as the Dry season intensifies (July and August). When disturbed the Black Wallaroo will flee up into the escarpment and because of the latter's deeply dissected nature the Black Wallaroo will rapidly disappear from view. The species is very adept at both rapidly ascending and descending the escarpment with leaps of 3 meters or more in height to rocks and cliffs.

Reproductive behaviour

There is little known about the reproductive behaviour but large pouch young may be seen through the Dry season (June-September). Presumably these permanently emerge from the pouch with new vegetation growth at the inception of the Wet season.

Social organisation

Most observations of the Black Wallaroo are fleeting glimpses as it is said to be extremely wary. When seen it is typically as a solitary individual or a pair or trio. However, in one helicopter survey of its habitat a group of 12 was seen so under some circumstances individuals may aggregate. Densities of Black Wallaroos are typically low with a mean of 2.5 wallaroos per square kilometre in favoured monsoon forest habitat. Further information on the social behaviour of this species is wanting.

Further readings

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

Press, A.J. (1989). The abundance and distribution of Black Wallaroos Macropus bernadus and Common Wallaroos Macropus robustus on the Arnhem Land Plateau Australia. In, Kangaroos, Wallabies and Rat-kangaroos Volume 2, ed. by G. Grigg, P. Jarman and I Hume, pp. 783-786. (Surrey Beatty & Sons, Sydney)

Telfer, W.R. and Bowman, D.M.J.S. (2006). Diet of four rock-dwelling macropods in the Australian monsoon tropics. Austral Ecology 31, 817-827.