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

Northern Bettong

Bettongia tropica ('tropical bettong')

Best place to see

Davies Creek National Park, Queensland

Davies Creek National Park is close to Cairns (53 km via the Kuranda Range) and about 10 minutes drive from Mareeba. The boulder-strewn Davies Creek cuts through the park which has granite outcrops and wet sclerophyll open forest. The park roads are subject to flooding and enquiries should be directed to the Cairns office of the Queensland Parks and Wildlife Service during the Wet season.

Accommodation is available in nearby towns and the Park has several campgrounds along Davies Creek. Campers need to be self-sufficient for cooking and bring drinking water as the Creek water in not potable. The Park has a number of walking trails including the easy grade 1.1 km Davies Creek Falls circuit.

Identification

Northern Bettongs average 1.2 kg and reach a weight of 1.4 kg. The Northern Bettong has a grey-brown back with silver guard hairs terminating in a white tip. The face is brown, and the ears are  medium brown and the sides of the body are a pale brown. The underside of the Bettong is pale blue-grey. The base of the tail is similar to the back colour but there are pale guard hairs that are gradually replaced by dark hairs and so the distal third of the tail is dark brown to black. The terminal end of the tail has a small brush. The underside the tail near the body is rufous and then changes to a terminal silver colour. The hind-feet and fore-paws are pale brown. The three central claws of the forepaws are curved and much longer than the two outer ones.

Habitat

The Northern Bettong is a threatened species confined to north Queensland, inland on a strip of sclerophyll forest with a grassy understorey between Townsville and Cairns. This habitat is bounded on the seaward side by rainforest and the landward side by dry sclerophyll forest and typically is no more than 7-8 km wide. The forest contains a mixture of Eucalypts and an understorey of kangaroo grass (Themeda australis) and blady grass (Imperata cylindrica). These grasses are favoured for cattle grazing and the habitat is fire-prone which along with exotic predators are threatening factors to the Northern Bettong's persistence.

Foraging behaviour

The diet of the Northern Bettong is typical of the other bettongs with leaf and stem of plants and the fruiting bodies of hypogeous fungi dominating. They also eat fruits, seeds, tubers and bulbs of plants and fruiting bodies of epigeous fungi and some invertebrates like insect larvae. Fungi are present in the diet throughout the year making the greatest quantity in the Wet season and the greatest diversity in the Dry season (up to 50 taxa).

 

Their habitat is prone to fire and the quantity of fungi eaten is greater on unburnt sites. Diversity of fungi is greater on burnt sites and individuals maintain body condition so while fire frequency and intensity does not compromise the food supply, the Northern Bettong can cope with some fire in its habitat. Low to moderate intensity fires  every 3-4 years may benefit this fire-adapted species as they will preferentially forage on burnt habitat in such conditions and their rate of discovery of fungi increases.

Reproductive behaviour

The Northern Bettong like most of the rat-kangaroos has a gestation period (21 day) just shorter than the oestrous cycle (22.5 day) 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 3.5 months and thus they are able to produce more than one young per year.

 

The reproductive behaviour of the Northern Bettong has not been studied but is likely to be similar to the Rufous Bettong.

 

Social organisation

Northern Bettongs occupy large home ranges averaging 59 ha and ranging from 19-138 ha in one study. Males maintain nests in a larger 'core' area (10 ha) than females (5.5 ha). Thus males may overlap some female home ranges. Foraging behaviour is evenly distributed across these home ranges and is not random. On discovery of a fungal body they adopt area-restricted searching with frequent and acute turns to encounter clusters of food. The population density is typically low ranging from 1.5 to 7.5 bettongs per km². In contrast, the Rufous Bettong can reach population densities of 36 per km². Historically there may have been genetically distinct northern and southern populations which have more recently converged again.

 

Further readings

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

Pope LC, Estoup A, Moritz C (2000) Phylogeography and population structure of an ecotonal marsupial, Bettongia tropica, determined using mtDNA and microsatellites. Molecular Ecology 9, 2041-2053.

Vernes K, Haydon DT (2001) Effect of fire on northern bettong (Bettongia tropica) foraging behaviour. Austral Ecology 26, 649-659.

Vernes K, Castellano MJ, Johnson CN (2001) Effect of season and fire on the diversity of hypogeous fungi consumed by a tropical mycophagous marsupial. Journal of Animal Ecology 70, 945-954.

Vernes K, Pope LC (2001) Stability of nest range, home range and movement of the northern bettong (Bettongia tropica) following moderate-intensity fire in a tropical woodland, north-eastern Queensland. Wildlife Research 28, 141-150.