Barrow Island Euro

The common wallaroo is often solitary, occupying a relatively small, stable home range near to a rocky outcrop or water, and moving out of rough country to graze on grasses and shrubs in adjoining areas (2) (4) (9). Small groups sometimes form around favoured resources, but are usually quite loose in size and composition (2) (6). The common wallaroo is able to survive harsh conditions by using caves and rocky outcrops for shelter, and appears to be able to go for as much as two to three months without drinking, surviving solely on the water contained in food plants (2) (9). The common wallaroo is believed to be polygynous (6) and is an opportunistic breeder, able to breed throughout the year, although often ceasing reproduction during prolonged droughts (2) (8) (10). A single, tiny young is born after a gestation period of 30 to 38 days (8), after which it climbs, unaided, through the female's fur and into the pouch, where it attaches to a teat and begins to suckle (11). Most development takes place within the pouch, the young common wallaroo emerging after around 231 to 270 days (8). The young is suckled for at least 12 to 14 months, with males reaching sexual maturity at around 18 to 20 months in captivity, and females at 14 to 24 months (8). Individuals may live for over 18 years in the wild (2). In a process known as embryonic diapause, the female common wallaroo is able to become pregnant again shortly after giving birth. However, the new embryo remains dormant until the first young is ready to leave the pouch or is lost, after which the embryo resumes development and is born when the pouch is vacant. This unusual form of reproduction, found in many kangaroos, means the female can quickly replace young lost to predators or drought, and can have embryos ready to develop as soon as conditions become favourable (2) (11).

The mainland populations of the common wallaroo are widespread and abundant, and are present in a number of protected areas (1). Commercial take is regulated under nationally approved management plans (1) (7), which aim to maintain populations of common wallaroo in an ecologically sustainable manner (10) (12) (13). Barrow Island is also protected as a nature reserve (3) (4). Conservation priorities for the vulnerable Barrow Island wallaroo include determining the extent of nutritional stress in the population, continuing with long-term population monitoring, and determining if oil field management can be modified to improve the condition of the wallaroo population. It will also be important to prevent introductions of non-native species, to monitor and improve traffic management to reduce road fatalities, to develop an appropriate fire management strategy, and to restore land impacted by the oil field (5) (7).

The common wallaroo is a rather stocky kangaroo with coarse, shaggy fur, a hairless muzzle, a relatively short, thick tail, and a distinctive upright hopping style (2) (3) (4) (5). The robust body shape, with shorter limbs than other kangaroos, may be an adaptation for leaping around on rocks, and the short, broad hind feet have roughened soles to give extra grip (4). The male common wallaroo is up to twice the size of the female, and has particularly thick-set shoulders and forearms (4) (6). Coat colour varies from reddish-brown to a very dark blue-grey, almost black, and is generally lighter on the underparts (4). Four subspecies are recognised, based mainly on colour, size, and genetic differences: Macropus robustus robustus (eastern wallaroo), Macropus robustus erubescens (inland wallaroo or 'euro'), Macropus robustus woodwardi (northern wallaroo), and Macropus robustus isabellinus (Barrow Island wallaroo). In some areas, M. r. robustus and M. r. erubescens overlap and are thought to hybridise (4). The Barrow Island wallaroo, M. r. isabellinus, is the most distinctive of the subspecies, being smaller and stockier, reaching only half the size of the other forms (3) (4).

Often referred to as a 'hill kangaroo', the common wallaroo typically inhabits mountainous areas, rocky hills and steep escarpments, although it may also use stony rises, grasslands and plains (2) (4) (7) (8). Caves, overhanging rocks and ledges are often used for shelter, particularly from extreme heat, and as refuges from predation (1) (2) (4) (8). The species may also shelter in dense shrub around streams (1).

The common wallaroo is widely distributed throughout most of Australia, except Tasmania (1) (2), although the distribution is rather patchy due to the discontinuous nature of the habitat (4). M. r. robustus occurs in eastern Australia, from southern New South Wales to Queensland, M. r. erubescens occurs over much of the drier areas of the continent, from western New South Wales and Queensland, west to the Indian Ocean coast, and M. r. woodwardi occurs across northwestern Australia (4). M. r. isabellinus is found only on Barrow Island, off the coast of Western Australia (1) (4) (7).

Classified as Least Concern (LC) on the IUCN Red List (1).

There are not thought to be any major threats to the common wallaroo (1) (4), and the steep, rocky areas it favours help to protect this species to some degree (4) (10). In addition, like many other large kangaroo species, the common wallaroo may have benefitted from artificial water holes provided for livestock, as well as a reduction in dingo numbers and the presence of sheep, creating favourable grazing conditions (2) (9) (10) (11). Although the common wallaroo is legally culled in some areas for food, skins, and because of alleged damage to pastures and crops (2) (7) (10) (11), it is estimated to make up only about three percent of the overall commercial kangaroo quota (4). However, there is some controversy over how many kangaroos can be safely harvested, particularly in light of increasing human habitat modification and drought (2). The Barrow Island wallaroo, M. r. isabellinus, may be more vulnerable than the mainland subspecies, particularly in light of its smaller, isolated population, estimated to number only around 1,800 individuals (4) (7). This distinctive subspecies is listed as Vulnerable under the Environmental Protection and Biodiversity Conservation Act 1999 (EPBC), with threats including inappropriate fire regimes, introduced species, road fatalities, and habitat degradation associated with the development of oilfields (3) (5). The population has also recently been found to suffer from anaemia and poor condition, possibly related to nutritional stress (1) (7).