The antilopine wallaroo is this country’s only large kangaroo that lives entirely in the tropics. Unlike some kangaroo species, its numbers aren’t in great abundance and it may even be under threat. CRC PhD student Euan Ritchie is studying its biology so we can develop conservation and management regimes that will help it survive.

The antilopine wallaroo is Australia's only large tropical kangaroo Photo: David Webb

Behaviour | Distribution | Wallaroo snapshot | Cape York biodiversity | Stakeholder cooperation | More Reading | 

Macropods are among Australia’s most recognisable group of marsupials; they include kangaroos, tree kangaroos, wallaroos, wallabies, rock wallabies, bettongs, potoroos and the quokka. Of Australia’s 50 recent macropod species, six are now extinct and 11 are declining (Johnson et al. 1989).

Until recently it was thought that the fauna of Australia’s monsoonal tropics remained largely intact. But at present a large-scale mammal decline appears to be occurring throughout this region, particularly within savanna environments. Researchers such as John Woinarski warn that past extinctions in central Australia were extremely rapid, with changes in abundance leading to the loss of species within one to two decades. Further work by Don Franklin details widespread declines of granivorous birds that overlap those areas with reported mammal declines.

Within the vast area of Cape York and the Einasleigh Uplands (Figure 2) lives one of Australia’s most distinctive animals: the antilopine wallaroo ( Macropus antilopinus ). When Gould (1842) named the wallaroo he thought they resembled Africa’s antelopes: the males have a brick red colour on their back extending all the way to their head, with their front a vivid creamy white. Gregarious, grass-eating and tropical, antilopine wallaroos also occur in smaller numbers in the Top End of the Northern Territory and the Kimberley region of Western Australia.

However, observations in Cape York Peninsula have shown widespread mammal declines, including declines of antilopine wallaroos. So at a time when it seems there are kangaroos everywhere and they are being culled in certain parts of Australia, this particular species is under threat—and it may be the first observed decline of a kangaroo since European settlement.

Photo: David Webb

There are a number of potential causes for these declines: habitat change and clearance, introduced predators and competitors, intensification of grazing and agriculture, introduction of exotic diseases, changes in fire regimes and overkill.

Of the six living species of kangaroo, none have been listed as endangered to date. Typically kangaroos have prospered as a result of the land management practices associated with livestock grazing, such as permanent water sources being established, woodland being cleared in favour of grasslands and the removal of predators, particularly dingoes. However, like many mammal species of northern Australia there is very little known about the wallaroo: its diet, breeding habits, biology—all are something of a mystery. This means we have no basis to interpret the causes of the declines that have been observed, or to recommend appropriate management of habitat to prevent further declines.

Given that the antilopine wallaroo is harvested as a bush food by Aboriginal communities, our estimates of population size, distribution and reproductive rates will allow us to estimate sustainable harvest rates. The study will also result in a better understanding of recent ecological changes on Cape York Peninsula, and their effects on wildlife.

Figure 1: Distribution of antilopine wallaroos: Dark blue represents the species core distribution and light blue the periphery. Dots represent known locations of antilopine wallaroos.

Figure 2: Queensland distribution of antilopine wallaroos

Behaviour

The animal is quite striking and beautiful to look at; but over the course of my study, I’ve noted something even more striking: antilopine wallaroos display a behaviour known as sexual segregation. Outside of the breeding season, these wallaroos separate into single sex groups with large groups of females (5–10 individuals) and bachelor groups comprising large-sized males (3–5 individuals).

Why do they do this? Some theorise that females make different diet choices because their reproductive role and smaller body size means they have higher relative energetic needs—but activity patterns and risk of predation could also play a part.

My observations have confirmed that diet choice may indeed play a significant role. While both males (85%) and females (74 %) feed on large amounts of grass, females feed on significantly more forbs, which have a higher nutrient content than grass. Within my study site, forbs were less abundant and more patchily distributed than grass, so this could explain the group splitting between males and females. However, other mechanisms could also offer explanations, so more research is needed.

Because of this split between male and female, males spend long amounts of time with each other, some of which is spent establishing a dominance hierarchy, which seems to be related to reproductive success. The hierarchy determines which male in any chosen group is the strongest, and therefore most likely to succeed in male versus male competition for females, and ultimately who will mate with females in the breeding season.

Wallaroo snapshot

Over the past 12 months I have recorded almost 3000 wallaroos, and it appears that population numbers are relatively stable in Queensland—interestingly, the area with the highest abundance is on a cattle station that is cell grazed—an unusual grazing practice in Cape York—and has not been burnt for 10 years. This could mean that the antilopine wallaroo is sensitive to fire.

However, my findings are no cause for complacency, because wallaroos are most abundant in the better grazing lands of north Queensland around the basalt belt of Mount Surprise (Figure 2). This could eventually be a problem for graziers who want to expand their business while preserving habitat for native species such as the wallaroo. Numbers in the Kimberley and Northern Territory do not fare as well, but more research is needed to pin down the probable causes for declines in those regions.

Stakeholder cooperation

The nature of my work requires interaction with a broad spectrum of individuals and communities, including graziers, Indigenous people, and park rangers. The cooperation between these groups has been inspiring, and I am thankful that this is the case, as these are the people who will shape the future of our tropical savannas.

An article on Euan’s findings will also appear in the next issue of Nature Australia , due out in December.

More Reading

Croft, D.B. 1987, ‘Socio-Ecology of the Antilopine Wallaroo Macropus Antilopinus in the Northern Territory Australia with Observations on Sympatric Macropus-Robustus-Woodwardii and Macropus-Agilis’, Australian Wildlife Research , 14(3) 243–256.

Russell, E.M., & Richardson, B.J. 1971, ‘Some observations on the breeding, age structure, dispersion and habitat of populations of Macropus robustus and Macropus antilopinus (Marsupialia)’, Journal of Zoology , London 165:131–142.

Woinarski, J.C.Z., Milne, D.J. & Wanganeen, G. 2001, ‘Changes in mammal populations in relatively intact landscapes of Kakadu National Park, Northern Territory, Australia’, Austral Ecology , 26:360–370.