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

Barrow Island Wallaroo (Euro)

Macropus robustus isabellinis ('Isabelle's robust long-foot')

Best place to see

Barrow Island, Western Australia

Barrow Island was isolated from mainland Western Australia about 8,000 years ago by rising sea levels. It now forms Western Australia's second largest island (234 square kilometres) and is 56 km off the north-western coast about 1300 km from Perth. The process of isolation carried with it an ark of animal species. Amongst these are mammals that are threatened or extinct on mainland Australia. Isolation on Barrow Island of the Common Wallaroo has lead to sufficient genetic drift to be recognised as a sub-species. However, Common Wallaroos on both the mainland and Barrow Island share a distinctive red colouration rather than the predominantly browns, greys and blacks of the eastern populations. The island has three other macropod species - Boodie (burrowing bettong), Spectacled Hare-wallaby, Black-footed Rock-wallaby - amongst its 15 species of mammals, as well as 110 species of birds, 54 species of reptiles and one species of frog. Green and Flatback turtles breed along its coastline.

In 1910, Barrow Island was declared a Class A Nature Reserve and was relatively pristine since it did not readily support pastoralism. Most exploitation was of marine resources such as turtles and peal oysters. However, in the 1950s oil was discovered but exploitation was delayed by the use of nearby Montebello Islands (about 16 km north) as an atomic testing site for the United Kingdom. This lead to the island's 'dubious' protection until the early 1960s when oil drilling commenced. By 1966 100 million barrels of oil had been produced and average production today is about 14,000 barrels with an expected lifetime through to 2020. Oil production has managed to be conducted with due environmental care over four decades without species loss. Even so impacts typical of human habitation and industry occur including roadkill, addition of water resources, nutrient outflows and the obvious excision of land for the oil industry. There is current concern about a large increment in industrial activity through the Gorgon Gas Project that will add a large-scale gas processing plant and associated equipment to the island.

Some general information about Barrow Island can be found at www.abc.net.au/nature/island/ep3/default.htm. Chevron Asiatic (www.chevron.com) operates the oil production and some counterviews about sustainability of the conservation values of the island can be found at www.rescuebarrowisland.org.au. The island is accessed from the port of Onslow, 88 km to the southeast.

Identification

The Barrow Island Wallaroo is the isolated island sub-species of the most widespread kangaroo, the Common Wallaroo (or Hill Kangaroo). Common Wallaroos have a large naked rhinarium giving them a dark shiny ‘button nose’ like koalas and wombats. They have no facial stripe but they do have large rounded ears. Their coat is coarser and shaggier than the fine down of Red Kangaroos. Females are relatively short and small and rarely exceed 25 kg. Their coat colour is distinctively reddish and similar to the male Antilopine Wallaroo. Males are short but very stocky with pronounced forearm musculature when mature. They reach around 50 kg on the mainland (the Barrow Island sub-species is smaller like many island species) and show a similar variation in coat colour to females.  The underparts are lighter and the tail tip is light coloured.

Common Wallaroos hop on their short legs in an upright posture, which seems less elegant than Red and Grey Kangaroos on flat ground, but comes to the fore as they effortlessly bound up rocky slopes. Barrow Island is deeply dissected with limestone caves which favour rock-haunting species even though the island itself is relatively flat.

Habitat

Barrow Island has many contrasts in landform and includes limestone uplands, intermittently flowing creeks, red and white sands, dunes, clay and salt flats and is surrounded by beaches. The highest point is 65 m and seems an unusual place for a hill-dwelling macropod but the landscape is deeply eroded forming gullies and cliffs. The Barrow Island Euro can be found across most the island including lounging on the beaches.

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Foraging behaviour

The Barrow Island Wallaroo's behaviour has been little studied but is assumed to be similar to the Euro on the mainland. The Island has bout 230 species of plants but 90% is covered with spinifex - a tussock grass well-adapted to the arid climate of the Island. The Wallaroo can eat spinifex and consumes the seed head during the autumn/winter flowering season. The ability to recycle nitrogen (urea) through the saliva makes the Common Wallaroo the best able of the large kangaroos to survive on the spiky and generally poor nutrition of the spinifex. These abilities were discovered in extensive ecological and physiological studies of the Euro in the nearby Pilbara region of Western Australia.

Reproductive behaviour

The Common Wallaroo is a continuous breeder and may have three overlapping generations of offspring - a young-at-foot, a pouch young and a diapausing blastocyst in utero. Oestrus is part-partum and males regularly check the reproductive status of females. Male dominion at a mating event is usually related to body size and the consort male may be accompanied and challenged by a bevy of importunate males.

Social organisation

The Common Wallaroo is generally solitary with strong bonds only between a mother and her dependent young-at-foot. The limited land area available to an island population may lead to greater aggregations of Barrow Island Wallaroos especially at limited water sources and resting sites.

Further readings

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