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 Bettongs, Potoroos and Musky Rat-Kangaroo are collectively known as the Rat-kangaroos. In fact, they form two families, the Potoroidae, which includes all the potoroos and bettongs, and, the Hypsiprimnodontidae, whose sole living representative is the Musky Rat-kangaroo. They are observationally distinguished from the kangaroos and wallabies by their diminutive body size but the largest species, the Rufous Bettong, eclipses the smallest Rock-wallabies, the Monjon and Narbelek. In general, they retain more 'primitive' ancestral characteristics with a partly prehensile tail to entrap grasses and sticks for nesting and a simpler stomach (and consequently richer diet). The forelimbs and hindlimbs are more similar in size than the gross differences in the kangaroos and wallabies, and so bounding as well as hopping is a mode of progress. Perhaps possum-kangaroo is more accurate but the first European observers were more familiar with rats than possums.

If you find an intact skull on your exploration of rat-kangaroo habitat then the dentition is clearly distinguishable from the kangaroos. They are more buck-toothed with the second and third incisors smaller than the first and more lateral in the upper jaw. The upper canines are well-developed whereas they are lost in the Macropdodidae. The premolar is large and blade-like and the molars are retained rather than lost anteriorly through wear and progress along the tooth row.

The rat-kangaroos have fared very poorly with the advent of agriculture and pastoralism compounded by the introduction of competitors (European rabbits and hares) and predators (Red foxes and domestic cats). The Potoroids generally have much reduced ranges relative to the first settlement of Australia by Europeans and two of the 10 species are extinct. The most dramatic of the declines is the Boodie (Burrowing Bettong) which was widespread across the rangelands of Australia and ended up marooned on a few offshore islands in Western Australia. Reintroductions are in progress and this species is on the first hops to making a comeback on the mainland. Like the Potoroids, the Musky Rat-kangaroo has lost much of its habitat in the highly prized real-estate of the tropics.

Species

Rufous Bettong

Aepyprymnus rufescens ('Reddish high rump')

Best place to see

Wallaby Creek, New South Wales

The Rufous Bettong has the broadest range of all the rat-kangaroos and can potentially be seen in a number of National Parks in northern NSW and Queensland. The chosen destination is private property and celebrates the outstanding body of research on the behaviour and ecology of macropods that emerged from this property and the surrounding area from the early 1970s. A key attraction is the very high diversity of species (9) of which the Rufous Bettong is one. However, the property is best known to the public from the works of documentary film-makers.

The property is listed on a number of tourism information and booking sites. The property offers accommodation for six in a cabin with linen supplied and takes one booking at a time. The nearest town in Urbenville and it is within a day's drive of Brisbane.

Identification

The Rufous Bettong is the largest of the rat-kangaroos with a weight range between 3 and 3.5 kg. The fur is long and reddish-brown through to pale grey with dark and red flecks. The rhinarium of the nose is bare but the face and muzzle are hairy. The eyes are marked by a thinly furred surround with skin showing through. The underside and forepaws are light coloured.

Habitat

The Rufous Bettong has the broadest current distribution of the rat-kangaroos and is found on both sides of the Great Dividing Range in north-eastern NSW and Queensland. The population around Barrington Tops in NSW is disjunct from rest of the species' distribution. Rufous Bettongs are found in many forested habitats like coastal eucalypt and tall wet sclerophyll forests through to dry, open woodland in the western margins of their range. The prefer a sparse understorey of native grasses, particularly Blady Grass (Imperata cylindrica) and various species of Poa. Their density is difficult to estimate because of their small size and cryptic habits but seems to be higher in the more tropical end of their range. They are generally found at low elevations on valley floors (alluvial flats) and use grass tussocks and hollow logs for shelter rather than shrubs and so are in relatively open habitat like Eastern Grey Kangaroos.

Foraging behaviour

The diet of the Rufous Bettong diverges from the other rat-kangaroos as they eat mainly roots and tubers. In their contemporary habitat many of these are supplied by introduced flatweeds (Hypochoeris, Centaurea and Taraxacum). Hypogeous and epigeous fungi are eaten in the wet season in common with other rat-kangaroos. They also eat flowers, grass and grass-seed and in common with other rat-kangaroos are not strictly vegetarian and will consume invertebrates.

 

Their habitat is prone to fire and blady grass is often purposely burnt to stimulate new green pick for cattle. Provided cover remains in a patchwork or mosaic burn, the Rufous Bettong is advantaged by the maintenance of open habitat by fire and access to the roots and tubers on burnt areas.

 

Reproductive behaviour

The Rufous Bettong like most of the rat-kangaroos has a gestation period just shorter than the oestrous cycle and thus has a post-partum oestrus with mating taking place very soon after the current pouch young vacates the pouch permanently. They show embryonic diapause and breed continuously regardless of season. Pouch life is around 4 months and thus they are able to produce more than one young per year.

 

The Rufous Bettong is not sexually dimorphic and ardent males are repelled by similar sized females with kicks from a sideways prone position if the female is unreceptive. As the female approaches oestrus (receptivity) she and her male consort hop around in tandem until the male mounts grasping the female around the flanks with his forelimbs. The male may grasp and bite the female's neck to hold the mounting position leaving a disturbed patch on the female's back as evidence of mating. In captivity, females are relatively tolerant of each other but males violently attack each other resulting in wounding. This behaviour is inconsistent with observations of free-living bettongs.

 

Females in oestrus attract multiple males and the consort maintains a relationship with the female without overt aggression to other males. Primacy in the association seems to be the key and successful males go to the nest of females early in the evening to establish a consort relationship. Some males regularly associate with particular females in or out of oestrus and likely preferentially mate with them. Genetic analysis has shown that variance in male mating success is low (maximum of 14% paternity to one male) and not skewed to one or a few dominant individuals. Males frequently sire young with the same female and so a basically promiscuous mating system is overlaid on some individual longer term relationships. This pattern is found in some populations of baboons where many females in a group may mate with the current dominant male but some mate with a partner with which the frequently associate.

 

Social organisation

Rufous Bettongs will be typically seen alone but males and females whose home ranges overlap may associate as a pair over the night-time foraging period. Groups of the same sex are rare and aggregations if they occur are small (~ 6 individuals). Females are more philopatric (stay or in natal home range) than males who disperse over distances as long a 6.5 km. Dispersal is not a function of population density and  there appears to be independent regulation of population size relating to local resources. Thus rather than a few large founder (source) populations in rich habitat vulnerable to severe perturbation by habitat loss, equal exchange to many small, medium and large populations occurs. This may have assisted the Rufous Bettong to persist over most of its geographic range where other rat-kangaroos suffered widespread extinction with the advent of forestry, agriculture and pastoralism.

 

Further readings

Claridge AW, Seebeck JH, Rose R (2007) 'Bettongs, Potoroos and the Musky Rat-kangaroo.' (CSIRO Publishing: Melbourne)

Frederick H, Johnson CN (1996) Social organisation in the rufous bettong, Aepyprymnus rufescens. Australian Journal Of Zoology 44, 9-17.

Pope LC, Blair D, Johnson CN (2005) Dispersal and population structure of the rufous bettong, Aepyprymnus rufescens (Marsupialia: Potoroidae). Austral Ecology 30, 572-580.